203 Roadway Excavation and Embankment
Importance of Proper Embankment Construction
Importance of Proper Excavation
Embankment Construction Methods (203.05)
Spreading and Compacting (203.06)
Compaction and Moisture Requirements (203.07)
Method of Measurement (203.09)
Documentation Requirements – 203 Roadway Excavation and Embankment
Introduction
After many years of solving soil and rock problems throughout the state, the author of this section can assure the reader of ‘One Constant’.
“Soil and Rock Conditions Vary, Vary and will Vary Again.”
The author could repeat this statement a hundred times throughout this manual and it would be a hundred times too few.
Earthwork consists of roadway excavations (cuts) and roadway embankments (fills) for highways and associated items of work. Earthwork includes all types of materials excavated and placed in embankment, including soil, granular material, rock, shale, and random material. Associated items of work considered to be in the broad range of earthwork that includes: preparation of foundations for embankment, disposal of excavated material, borrow, preparation of the subgrade, proof rolling, rock blasting, base construction, and berm aggregate construction.
If pavement is to remain smooth and stable during years of service under traffic, the earthwork on which it is built must be stable and must furnish uniform support. Where roughness, settlements and other distress develop in pavement during service under traffic, the cause often is a deficiency in the stability of earthwork, which supports the pavement.
Uniformity of earthwork is necessary and important to obtain high stability and long-term performance at all locations throughout the length and width of the project. Consider, for example, a highway project where 95 percent of the earthwork was performed according to the specifications. But 5 percent was non-specification and low-stability material, which appeared in many small areas throughout the project. Pavement roughness and distress developed in these areas during service under traffic loading. Such a project probably would be evaluated by the traveling public as a “rough job” or a “poorly constructed” project. No notice or credit would be given to the 95 percent of the work, which was constructed properly. The entire project might be discredited and be considered poor because a relatively small proportion of the project was constructed with poor earthwork construction procedures or practices.
The foregoing assumed example is intended to illustrate the need for consistent compliance with earthwork specifications in all areas, both large and small, throughout the length of the project, and throughout the time from the beginning to the end of earthwork construction.
Importance of Proper Embankment Construction
The embankments that ODOT constructs are structures. The success of these structures is directly proportional to the project’s emphasis on correct embankment techniques.
The importance of proper construction practices during construction cannot be overemphasized. The results of improper construction practices may or may not show up during construction. But, these improper practices will eventually become evident at some point during the life of the embankment structure.
The construction requirements in the specifications are written to maximize the embankment structure’s life. When the specifications are not followed, the life expectancy will decrease and the future maintenance cost will increase.
The embankment structure is shown in Figure 203.A. The structure consists of three main components:
1. Foundation
2. Embankment
3. Pavement
A geotechnical engineer ensures that the embankment will be stable as designed. The pavement is constructed on top of the embankment.
Figure 203.A – Embankment Structure
The embankment that is shown in the plans structurally bridges the foundation and supports the pavement. The embankment is built by compacting layers of materials in horizontal lifts, as shown in Figure 203.B. These lifts consist of soil, granular material, rock, shale, asphalt, concrete, or recycled materials. The embankment’s resistance to movement relies on the proper construction of these lifts. These lifts work together as a unit to resist the loads.
Figure 203.B – Embankment Layers
A condition such as the one in Figure 203.C can occur if an embankment is not properly constructed. When this condition occurs the Factor of Safety is less than 1.0 and the embankment fails.
Figure 203.C – Embankment Failure
A factor of safety is the ratio of the Resisting Forces divided by the Driving Forces, as shown in the following equation.
Minimum factors of safety for embankment structures are low, on the order of 1.2 to 1.5. Figure 203.D illustrates the resisting and driving forces. The weight of the fill works to move the foundation and the embankment counter clockwise to the right. The internal strength of the embankment layers and the foundation work together to support the pavement. Failure may occur in a circular fashion as shown, in a semi-circle, in a block mode or wedge. The basic principles are the same in all three modes of failure.
Figure 203.D – Resisting and Driving Forces for Embankment Failure
Importance of Proper Excavation
Proper excavation techniques in cut sections are just as important as embankment construction; the only difference is that in the failure mode the rock or soil falls onto the roadway instead of the roadway failing.
This is illustrated in Figures 203.E-1 and 203.E-2. If a soil cut is cut too steep then the soil can flow on to the roadway as illustrated in 203.E-1. This figure shows a deep-seated wedge failure. This failure can occur in an embankment condition also.
Figure 203.E-1 – Cut Slope Failure (deep seated wedge)
Figure 203.E-2 – Cut Slope Failure (rotational failed condition)
Figure 203.E-2 details a rotational failed condition on the left. The right side shows a design that is properly benching so that it reduces the driving forces. If a rock cut is cut too steep, the rock can fall on the roadway.
Figure 203.F – Falling Debris from Vertical or Nearly Vertical Faces near Roadway
The above rock and soil conditions can be avoided during the design or construction of a project. Ensure that the plan intent is followed in these cut locations on the project. Rock and shale excavations will be detailed under Section 208 Rock Blasting.
Materials (203.02)
The biggest changes in the 2002 version of the specification were the definitions and material requirements of the type of material allowed under the specifications.
In order to properly detail the requirements, it was necessary to divide up natural and recycled material requirements. Too many times in the past Contractors would try to obtain approval for materials that were not intended under the specifications.
A natural material is a material that was created by nature; a material that is mined or excavated and graded is a natural material. A material that is chemically altered by a manufacturing process such as concrete, fly ash, foundry sand, or slag is a recycled material.
Materials are defined in 203.02. As the materials are defined in 203.02, all of the allowed materials are detailed in 203.02.R as “Suitable Materials.” Specific, more detailed material requirements are located in 703.16.
In the following sections, the materials will be detailed in the specific 203.02 sections for clarity.
If there is any doubt on the condition, status, acceptability, or approval of the materials throughout the following sections, then the project should contact one of the following: the District Engineer of Tests, the District Geotechnical Engineer, the Aggregate Section of the Office of Materials Management, or the Office of Geotechnical Engineering.
Natural Soil (203.02.I)
The definition for natural materials in 203.02.I is as follows: “All natural earth materials, organic or inorganic, resulting from natural processes such as weathering, decay, and chemical action.”
Allowable materials are materials such as clay, silt, sand or gravel. These are allowed as suitable materials and are further defined in 703.16.A.
Department Group Classifications A-4-a, A-4-b, A-6-a, A-6-b, and A-7-6 are allowed. All of these materials are fine graded and have more than 35 percent of the particles passing the No. 200 sieve. More detail can be found by examining Figure 203.G. These classifications are further defined on the right side of the chart under Silt-Clay Materials.
Materials must have a maximum laboratory dry weight of at least 90 pounds per cubic foot (1450 kg/m3). Materials that are less than this weight usually have too much organic matter or clay materials.
Soils that have a liquid limit in excess of 65 or identified as Department Group Classifications A-5, or A-7-5 are not allowed. The A-5 material is highly elastic by virtue of its high liquid limit. The A-7-5 material is highly elastic and subject to volume change.
Natural Granular Materials (203.02.H)
These materials are defined in 203.03.H as follows: “Natural granular materials includes broken or crushed rock, gravel, sand, durable siltstone, and durable sandstone that can be placed in an 8-inch (200 mm) loose lift.”
These materials are allowed in 203.02.R, Suitable Materials. The material requirements are further detailed in 703.16.B and 703.16.C.
Under 703.16.B, Department Group Classifications A-1-a, A-1-b, A-3, A-3-a, A-2-4, A-2-6, or A-2-7 are allowed. All of these materials generally are mixtures of coarse and fine graded materials. These materials have less than 35 percent of the particles passing the No. 200 sieve. More detail can be found by examining Figure 203.G. These classifications are further defined on the left side of the chart under Granular Materials.
Granular material classified as A-2-5 is not allowed because of its low weight, high optimum moisture, high LL, low PI, and its propensity to slough.
Section 703.16.C allows durable sandstone and durable siltstone. If these materials meet the slake durability requirements in ASTM D 4644, then the material is considered equivalent in strength and durability to other natural granular materials.
Section 703.16.C allows slags and recycled Portland cement concrete to be used as granular material types.
Contact the Office of Geotechnical Engineering to arrange for the appropriate materials testing if sandstone or siltstone is used for this application.
Figure 203.G - Department Soils Classification Chart
Identifying Soil and Granular Materials in the Field
It is sometimes necessary to make field decisions based on very little (if any) laboratory soils information. Or, it may be necessary to verify the accuracy of plan soil borings in the field. In these two cases and on other occasions, it is important to have a basic understanding of how to identify types of soils and granular materials in the field. The following is some, but certainly not all, of the methods that can be used to identify these materials in the field.
Granular Soils
Granular soils are easily identified by their particle size in the field. A sample may be taken inside and spread on a table to dry. A rough estimate of the material retained or passing each sieve may be obtained by examining the material when dry: the finer materials such as clays and silts cannot be separated and can only be distinguished between one another by a settling technique. This can be accomplished by using a hydrometer or by performing a crude settling test. This technique is beyond the scope of this manual.
Fine Grained Soils (Clays and Silts)
It is more important, yet harder, to distinguish between a clay and silt material in the field. Clays and silts should be treated and used differently in the field because of their difference in engineering and compaction properties. See the properties of soils in the next section.
A clay material can be easily rolled into a thread at moisture contents at, near, or above the plastic limit of the material. Clays can often be rolled into 1/8 inch (3 mm) diameter threads (about half the diameter of a pencil). See the plastic limit test later in this manual for further information. The thread may be easier and may be rolled into smaller sizes as the clay content increases. You cannot roll a pure silt material into a 1/4 inch (6 mm) thread no matter what the soil content.
Clay forms hard pieces that cannot be broken by hand pressure when it is dry. Place an irregular piece of dry soil between the index finger and the thumb, and try to break the material. If the material is difficult or impossible to break, it is probably clay. A silt or sandy material will generally break easily with this amount of hand pressure.
Clay fines are generally greasy, soapy, and sticky. When wet, clay dries slowly, while silt dries faster than clay.
When performing these hand techniques, observe the soil residue found on your hands for further information. If the soil on your hands is difficult to remove and the hands need to be rubbed briskly together to remove the soil, the material is probably a clay. A silt material is generally easily removed from the hands when rubbed together.
A silt material will react to vibration or shaking. Place a small amount of pliable soil in your hand. Hold the material in one hand and drop that hand on the other hand or a hard surface. Water will form on the surface of a silt material. You can also put the soil in a bowl and tap it on a table to get the same result. Clay will not react to this test.
The above crude identification techniques should not replace classification by the laboratory but should be used as a supplement.
If there is any concern, send a sample to the District Engineer of Tests for further classification as soon as possible.
Engineering Properties of Soil and Granular Materials
The following are general statements regarding the engineering properties of soil and granular materials. Consider these properties when solving field problems.
Properties of Granular Soils
1. Good foundation and embankment material.
2. Not frost susceptible, if free draining.
3. May erode on embankment side slopes.
4. Identified by the particle size.
5. Easily compacted when well graded.
Properties of Fine Grained Soils
1. Often have low strengths.
2. Plastic and compressible.
3. Lose part of their shear strength when wet or if disturbed.
4. Practically impervious.
5. Slopes are prone to slides.
Properties of Silts
1. High capillary action and frost susceptible.
2. No cohesion and non-plastic when pure silt.
3. Highly erodible.
4. Difficult to compact.
5. Release water readily when vibrated.
6. Acts like an extremely fine sand during compaction.
Properties of Clay as They Relate to Silt
1. Better load-carrying qualities.
2. Less permeable than silt.
3. Easier to compact than silt. (Any soil is easier to compact than silt.)
4. More volume change potential.
5. Plastic or putty-like property.
6. Clays are weaker when compacted wet of optimum.
Moisture Effects on Soils
Granular soils are less affected by the moisture content than clays and silts, have larger voids, and are free draining. Granular materials have relatively larger particles as compared to silts and clays.
Water content has a large effect on the physical properties of fine-grained soils. The Atterberg Limits are used to describe the effect of varying water contents on the consistency of fine-grained soils. See Figure 203.H.
Figure 203.H – Atterberg Limits
The plasticity index (PI) is used to classify soils. The plasticity index is calculated by subtracting the plastic limit (PL) from the liquid limit (LL) (e.g. PI = LL – PL). Liquid limits as well as plastic limits are the water content at the condition of the test.
Liquid Limit
1. State between the plastic solid and liquid state.
2. At liquid limit of 100 the soil contains equal weights of soil and water. (example Wc = Ww/Ws = 50/50)
3.
At liquid limit of 50, the soil is 2/3 soil and 1/3 water.
(example Wc = 33/66)
4. High liquid limit indicates soils of high clay content and low load carrying capacity.
Plastic Limit
1. State between semi-solid and the plastic solid.
2. The soil condition, when it contains just enough moisture to be rolled into an 1/8 inch diameter thread without breaking, just starts to break up.
3. Governed by the clay content.
4. The greater the clay content, the higher the plasticity (PI = LL – PL) and cohesiveness.
5. Load carrying capacity increases rapidly as the moisture content decreases below the plastic limit.
The following is a brief description of the characteristics of soils in the physical states.
Liquid Soil State Characteristics
1. Highly saturated state.
2. Flows under its own weight.
3. Very little or no friction between the particles.
Plastic State Characteristic
1. Soil can be remolded into various shapes.
2. Like modeling clay.
Semi-Solid Soil State Characteristics
1. No longer pliable.
2. Sample will crumble when rolled.
Brittle Solid Soil Characteristics
1. Soil ceases to change volume due to the loss of water.
2. No real engineering application.
Detailed Soil Property Explanation
Each term used in geotechnical engineering has specific meaning and application. Each soil test has specific meaning and application and indicates certain soil properties. Care in using correct terminology will prevent confusion and misunderstanding.
Soil
Soils have properties that influence their behavior and value. The properties of soil will vary with its gradation (composition), its moisture content, its vertical position in relation to the surface of the ground, and its geographical location. The more common properties encountered and used in highway work are defined and discussed in Section 203.
Most soils originally were solid rock; time and climate have broken the rock into progressively smaller particles. This can be shown in the laboratory by taking two or three pieces of gravel or stone and pulverizing them. First, sand-size particles can be made, then silt-size particles, and finally clay-size particles. However, chemical changes also take place as nature reduces rock into finer particles. Therefore, clay produced by nature over a period of many years will vary from clay-size material produced in a short time in a laboratory.
Particle Size
By naming and defining the size of the soil particles, all soil tests are placed on a common ground for comparison. The amount of soil retained or passing each sieve is one of the major tools used in judging, analyzing, and classifying a soil.
The quantities of each are determined by a laboratory analysis that separates the soil into groups of particle sizes. The standard methods of test prescribed by AASHTO T-88 and ASTM D-422 have been used widely in highway engineering and are used by the Department.
The distribution of particle sizes larger than 0.074 mm retained on the No. 200 (75 μm) sieve is determined by sieving, while the distribution of particle sizes smaller than 75 μm is determined by a sedimentation process, using a hydrometer to determine the necessary data.
Definitions of sizes used by the Department are the same as established by AASHTO T-88, with the exception of the definition of clay, and are as follows:
|
Component |
Size |
|
|
Boulders |
Larger than 12 inches (300 mm) |
|
|
Cobbles |
3 to 12 inches (75 to 300 mm) |
|
|
Gravel |
Coarse |
¾ to 3 inches (19 to 75 mm) |
|
Fine |
#10 sieve to ¾ inch (2 to 19 mm) |
|
|
Sand |
Coarse |
#40 sieve to #10 sieve (0.42 to 2.0 mm) |
|
Fine |
#200 sieve to #40 sieve (0.074 to 0.42 mm) |
|
|
Silt |
0.005 to 0.074 mm |
|
|
Clay |
Smaller than 0.005 mm |
|
Texture
The amount of each soil type (i.e., boulders, cobbles, silt, and clay) contained in a soil mixture determines its texture or feel. Classification of soils by texture must not be confused with classification of soils for engineering purposes. Sometimes they are similar but at other times they may be different. The amount of each soil type in the soil is determined by laboratory tests. These test results are then compared with the texture definitions in use to determine the texture name.
Soil texture is classified after its sieve size is determined. It is possible to make approximations of texture by the feel of moist soil when rubbed and ribboned between the thumb and index finger.
The texture of soil is given to tell as much as possible about a soil in a few words. Using a texture classification, approximations and estimates can be made of many soil properties, such as bearing value, water-holding capacity, probability to frost heave, permeability, etc.
Soil Components (Major and Secondary)
It is the practice of the Department to describe soil components and texture of a soil as follows:
Major Components
Major components are described as gravel, sandy gravel, gravelly sand, sand, silty sand, clayey sand, sandy silt, silt, clayey silt, silty clay or clay. More than 35 percent of the total sample is required in order to classify a major component. Where two words are used to describe the major component, the second word describes the greater quantity.
Examples: Sand predominates in “silty sand” while silt predominates in “sandy silt”.
Secondary Components
Descriptions of secondary components are preceded by the term listed below, according to the percent of total sample indicated:
|
Term |
Percent of Total Sample |
|
Trace |
0 to 10 |
|
Little |
10 to 20 |
|
Some |
20 to 35 |
|
And |
35 to 50 |
Examples of material texture descriptions based on component test results are as follows:
|
Material Components |
Texture Description |
|
Sand 30%, silt 55%, clay 15% |
“sandy silt with little clay” |
|
Sand 8%, silt 55%, clay 37% |
“silt and clay with trace sand” |
|
Gravel 20%, sand 68%, silt 12% |
“gravelly sand with little silt” |
|
Gravel 2%, sand 12%, silt 42%, clay 38% |
“silt and clay with little sand, trace gravel” |
Internal Friction
Internal friction is defined as the resistance to sliding within the soil mass. Gravel and sand impart high internal friction and the internal friction of a soil increases with sand and gravel content. For sand, the internal friction is dependent upon the gradation, density, and shape of the soil particle, and is relatively independent of the moisture content. Clay has a low internal friction, which varies with the moisture content. A powder-dry, pulverized clay has a much higher internal friction than the same soil saturated with moisture, since each soil particle can slide on adjoining soil particles much more easily after it is lubricated with water.
Various laboratory tests have been devised to measure internal friction. It is defined as the angle whose tangent is the ratio between the resistance offered to sliding along any plane in the soil and the component of the applied force acting normal (perpendicular) to the plane. Values are given in degrees. Internal friction values range from 0 degrees for clay just below the liquid limit to as high as 34 degrees or more for a dry sand. Very stiff clay may have a value of 12 degrees.
The governing test should be based on the most unfavorable moisture conditions that will prevail when the soil is in service. This “angle of internal friction” is not the same as the natural angle of repose or degree of slope on the soil in fills.
Cohesion
Cohesion is defined as the mutual attraction of particles due to molecular forces and the presence of water. The cohesive force in a soil varies with its moisture content. Cohesion is very high in clay but of little or no significance in silt and sand. Powder-dry, pulverized clay has low cohesion. However, as the moisture content is increased, the cohesion increases until the plastic limit is reached. Then the addition of more moisture reduces the cohesion. By partially over-drying wet clay, most free water is removed and the remaining moisture will hold the clay particles together so firmly and give the soil such high cohesion that a hammer may be required to break the particles apart. These conditions are illustrated, respectively, by the dry dirt road in summer that dusts easily but carries large loads; the muddy, slippery road of spring and fall; and the hard-baked surface of a road immediately after summer rains.
Various laboratory tests have been devised to measure cohesion. Results are usually given in pounds per square foot (psf) or kilopascals (kPa) and may vary from 0 psf in dry sand and wet silt to 2,000 psf (96 kPa) in very stiff clays. Very soft clays may have a value of 200 psf (10 kPa). The governing test should be based on the most unfavorable moisture condition that will prevail during service.
Internal Friction and Cohesion
The stability and hence the structural properties of soil are determined largely by the combined effects of internal friction and cohesion. In most soils these combine to make up the shearing resistance. The combined effects are influenced by other basic factors such as capillary properties, elasticity, and compressibility.
All these factors plus the site on which the soil is located determine the moisture content that will prevail in the soil in service. They also govern the load-carrying capacity of a soil, which is the primary concern. The clay-gravel road made up largely of gravel and sand, with a small amount of silt to fill voids and a small amount of clay to give cohesion, illustrates a soil of high bearing value produced by high internal friction due to sand and gravel and high cohesion due to clay. Clay illustrates a soil of low bearing value, because when clay is wet, internal friction is negligible since no coarse grains are present, and cohesion is low since it has been destroyed by moisture. The same clay, air-dry, will have high bearing value due to high cohesion brought about by the removal of moisture.
Capillarity
Capillarity is defined as the action by which a liquid (water) rises in a channel above the horizontal plane of the supply of free water. The number and size of the channels in a soil determine its capillarity. This soil property is measured as the distance moisture will rise above the water table by this action, and will range from 0 in some sand and gravel to as high as 30 feet (9 meters) or more in some clay soils. However, it often requires a long period of time for water to rise the maximum possible distance in clay soils because the channels are very small and frequently interrupted, and the frictional resistance to water is great in the tiny pores.
Moisture in silt soils may be raised by capillarity only 4 feet (1 meter) or so. Since the capillary pores are larger than for clay, a larger quantity of water is raised in a few days rather than over a long period. Silts are considered to have “high capillarity” by geotechnical engineers because of this rapid rise of water. The capillary rise in gravels and coarse sands varies from zero to a maximum of a few inches (centimeters).
Complete saturation of the soil seldom occurs at the upper limits of rise of capillary moisture. Capillarity of a soil and the elevation of the water table under the pavement determine whether the subgrade will become saturated in this manner. Whether or not the subgrade becomes saturated from capillary action (or from condensation, seepage, etc.) determines the bearing value of the soil to a considerable extent. Subgrade saturation by capillarity also determines whether frost heave and similar occurrences in subgrade will create a problem requiring treatment for satisfactory performance in service.
Compressibility and Elasticity
Compressibility and elasticity are the properties of a soil that cause it to compress under load or compaction effort, and to rebound or remain compressed after compaction. Most soils are compressible. Silty soils of the A-5 group are the most elastic of Ohio soils, and make poor subgrades for pavements. Fortunately, A-5 soils are limited in occurrence in Ohio. The A-7 soils in Ohio are moderately elastic, but do not present special problems in embankment or subgrade. A-4 soils are elastic under some moisture conditions, and sometimes present problems of stability during construction, but provide adequate support for pavements where good design and construction practices have been followed.
When a soil elasticity measurement is required, it is determined by special tests that simulate moisture changes and loading conditions anticipated in the field.
Elasticity and Deformation of Soils
When heavy rubber-tire construction equipment moves over an embankment layer foundation of wet fine-grained soil, some movement of the embankment surface occurs. One type of movement, called elastic movement, is described as follows: When the tire moves onto an area, the surface is deformed, and when the tire moves off the area, the surface rebounds, or springs back, with little or no permanent rutting of the surface. Cracking of the surface may or may not occur following this type of movement.
However, cracking occurs in cases of “pronounced” elasticity. In the case of pronounced elasticity or deformation, there is displacement of some surface soil to each side of the tire, with resulting deformation, rupture, cracking, and rutting.
The magnitude of the elastic movement or deformation may depend on one or more of a number of factors, including the following:
1. Weight of equipment.
2. Size of tires
3. Tire pressure
4. Soil moisture
5. Type of soil
6. Depth of soil layer
7. Stability of material underlying the soil layer being observed
Some embankment elasticity and deformation is expected under construction equipment loading. Moderate movement of less than a ½ inch (13 mm) can occur with heavy equipment weighting around 35 tons on embankments of satisfactory stability. This moderate movement is not considered detrimental. Greater movement is likely on adequately stable embankments under very heavy equipment weighting greater than 35 tons. Except for specialized situations, such as soft foundation soil at shallow embankment depth under the layer being observed, the greater movement due to these very heavy loads is not detrimental. In general, elastic or deformation movement under heavy or very heavy loads should be permitted if the moisture of the embankment is at least 2 percent below optimum.
Moisture control specifications are not intended to limit or restrict the use of very heavy construction equipment on embankment construction. The intent of the specifications is to limit the moisture to obtain a stable embankment.
The amount of elasticity and permissible deformation under any given load varies with job circumstances. For example, for the first layer over a soft original ground embankment foundation, considerable movement under loaded construction equipment is inevitable due to the soft foundation material. The resistance to deformation is more critical in the top portion of embankment, near the subgrade, than in lower portions of the embankment. If the lower embankment layers are low-stability material, such as wet silt, elasticity and deformation of the lower embankment layer must be closely monitored. This would not be necessary if successive embankment layers were of high stability material such as rock, shale, granular material, or dry soil.
Equipment which can be used successfully to test for embankment stability includes: rubber-tired roller, grader, loaded scraper, or loaded truck. Remember, more movement is to be expected under very heavy equipment than under heavy equipment ordinarily used in highway work. When rubber-tire construction equipment such as scrapers, graders or rollers, are being used over the entire general area during normal embankment construction operations, and observation shows no area of questionable stability, it is not necessary to have a piece of testing equipment systematically cover the entire area for the specific purpose of observing stability.
However, when the Engineer or Inspector questions or desires to check further the stability of an area during embankment construction, they are authorized to require the Contractor to move suitable equipment over the area to check for pronounced elasticity or deformation.
The determination of pronounced elasticity or deformation under the action of loaded rubber-tire construction equipment is based on the description given in the second paragraph of this section.
The administration of this requirement should be tempered with sound judgment backed by construction experience.
Shrinkage
Shrinkage refers to the apparent decrease in volume of a soil during its removal from the cut or borrow and its placement in the embankment. A greater density in the fill than in the cut or borrow area is the cause of the shrinkage. Shrinkage is not accounted for nor contemplated in the design of the project.
The amount of shrinkage resulting from increased density in the embankment material may be estimated by using a volume or dry density basis.
Either of the following equations can be used to calculate the Shrinkage Factor (SF).
Example of the use of a shrinkage factor:
The adjustment due to shrinkage is only used where the material is measured in a borrow pit and the embankment is placed outside of the plan allowed tolerances. Due to specification and design changes the use of borrow as a pay item should be minimized in the future.
Settlement and Scalping Losses
Losses due to scalping are usually insignificant as a percentage of the overall embankment construction quantities. Scalping losses of around six inches from the original cross-sections can be expected during construction. This is not compensated by the Department. If there is significant losses beyond this then it can be accounted for by taking cross-sections and compensation should be made.
Settlement of the embankment foundation can be an area where the contractor can lose material that is not measured directly. It can be accounted for in the earthwork quantity calculations.
Losses due to settlement of the embankment foundation, where the foundation is compressible, can be calculated by using settlement platforms. A settlement platform or several can be placed on the foundation. The platform is measured throughout the life of the embankment construction. A settlement verses time curve can be used to determine the amount of additional payment that is due. See Figure 203.I.
Figure 203.I – Settlement Curve
The amount of settlement that occurred over the life of the embankment construction is a function of this Total Settlement Curve. To make the additional embankment payment, multiply the settled amount by the length and width of the settled area. This length and width should be calculated at the half height of the embankment in the affected area. Some judgment is required as to the length of influence of individual or multiple settlement platforms.
In this example, the total settlement is as follows:
543.11 - 542.88 = 0.23 feet
Permeability
Permeability is a property of soil that allows it to transmit water. It is defined as the rate at which water is transmitted by soils. It depends on the size and number of soil pores and the difference in height of water at the point where it enters the soil and the point where it emerges. It is determined by tests on a representative soil sample and expressed as the coefficient of permeability, and it equals the velocity of water-flow in centimeters per second (cm/sec) under a hydraulic gradient of 1. A hydraulic gradient of 1 exists when the pressure head (or height of water) on the specimen in centimeters divided by the depth of the specimen in centimeters equals 1.
The permeability of a soil varies with such factors as void ratio, particle size and distribution, structure, and degree of saturation. Obviously, the permeability of a particular soil will vary with the degree of compaction since this influences the size of the soil pores. A particular soil loosely packed will be more permeable then the same soil tightly packed. Nature produces these differences, in connection with shrinkage forces that may be present, by surface freezing in winter (loosening a soil) and by repeated wetting and drying in the summer (consolidating the soil).
The coefficient of permeability, k, is used to determine the quantity of water that will seep through a given time and distance under a known head of water. It is calculated using the following equation.
The equation can be rearranged to find the quantity of seepage, Q, as shown below.
where:
Q = quantity of water, in cubic centimeters (cm3)
k = coefficient of permeability, in centimeters per second (cm/sec)
H = hydrostatic head, in centimeters
L = thickness of soil, in centimeters, through which flow of water is determined under hydrostatic head H;
A = cross-sectional area of material, in square centimeters (cm2);
t = time, in seconds (sec).
Tile can drain very porous soils, such as sands that have a k of 1.0 to 10-3 (0.001) cm/sec. Silty and clayey sand soils have a k of about 10-3 (0.001) to 10-7 (0.0000001) cm/sec. Highly cohesive clays have a k of less than 10-8 (0.00000001) cm/sec. It is difficult, if not impossible, to reduce the water content of soils by tile drains when the permeability coefficient is less than about 10-3 (0.001). For earth dams, the U.S. Bureau of Reclamation classifies soil with k values about 10-4 (0.0001) as pervious and soil with k below 10-6 (0.000001) as impervious.
Soil Group classifications A-6a, A6b and A-7-6 are generally considered impervious.
Plastic Limit
The plastic limit (PL) of soils is the moisture content at which a soil changes from a semisolid to a plastic state. This condition is said to prevail when the soil contains just enough moisture that it can be rolled into 1/8 inch (3.18 mm) diameter threads without breaking. The test, ASTM D-424 or AASHTO T-90, is conducted by trial and error, starting with a soil sufficiently moist to roll into threads 1/8 inch (3.18 mm) in diameter. The moisture content of the soil is reduced by alternating manipulation and rolling until the thread crumbles.
Clay content controls the plastic limit. Some silt and sand soils cannot be rolled into 1/8 inch (3.18 mm) threads at any moisture content; these have no plastic limit and are termed non-plastic. The test is of no value judging the relative load-carrying capacity of non-plastic soils.
A very important change in load-carrying capacity of soils occurs at the plastic limit. Load-carrying capacity increases very rapidly as the moisture content is decreased below the plastic limit. On the other hand, load carrying capacity decreases very rapidly as the moisture content is increased above the plastic limit.
Liquid Limit
The liquid limit (LL) is the moisture content at which a soil passes from a plastic to a liquid state. The test, ASTM D-423 or AASHTO T-89, is performed by determining, for various moisture contents, the number of blows of the standard cup needed to bring the bottom of the groove into contact for a distance of more than 0.5-inch (12.7 mm). These data points are then plotted and the moisture content at which the plotted line (called flow curve) crosses the 25-blow line is the liquid limit.
Sandy soils have low liquid limits of the order of 20. In these soils the test is of little or no significance in judging load-carrying capacity.
Silts and clays have significant liquid limits that may run as high as 80 or 100. Most clays in Ohio have liquid limits between 40 and 60.
High liquid limits indicate soils of high clay content and low load-carrying capacity.
Liquid limit can be used to illustrate the interpretation of moisture content as a percentage of the oven-dry weight of the soil. See an example in the previous section on liquid limit.
Plasticity Index
The plasticity index (PI) is defined as the numerical difference between liquid limit and plastic limit. Calculation details are included in ASTM D-424 and AASHTO T-90. The plasticity index gives the range in moisture contents at which a soil is in a plastic condition. A small plasticity index, such as 5, shows that a small change in moisture content will change the soil from a semisolid to a liquid condition. Such a soil is very sensitive to moisture unless the combined silt and clay content is less than 20 percent. A large plasticity index, such as 20, shows that considerable water can be added to the soil before it changes from a semisolid to a liquid.
When the liquid or plastic limit cannot be determined or when the plastic limit is equal to or higher than the liquid limit, the plasticity index is considered non-plastic (N.P.).
The moisture conditions at the plastic limit and liquid limit, and the plasticity index, often are called the “Atterberg Limits” (named after Albert Atterberg, the Swedish agricultural scientist who developed the concept).
Detailed Description of the Soil Classification Groups
The following is a brief description of the materials in each classification group detailed in Figure 203.G.
Group A-1
The typical material of this group is a well-graded mixture of stone fragments of gravel, coarse sand, fine sand, and a non-plastic or feebly plastic soil binder. However, this group may also include the same material without the soil binder.
Subgroup A-1a
This material consists of predominantly stone fragments or gravel, either with or without a well-graded soil binder.
Subgroup A-1b
This material consists of predominantly coarse sand either with or without a well-graded soil binder.
Group A-3
The typical material of this group is fine beach sand without silty or clay fines or with a very small amount of non-plastic silt. The group also includes stream-deposited mixtures of poorly-graded fine sand and limited amounts of coarse sand and gravel. These soils are sometimes difficult to compact similar to the A-4 group. The fineness of the material and the silt fines make stabilization difficult. See the group A-4 for further explanation.
Subgroup A-3a
This material consists of mixtures of coarse and fine sand with limited amounts of silt of low plasticity.
Group A-2
This material consists of a wide variety of “granular” materials which are borderline between Groups A-1 and A-3 and the silt-clay materials of Groups A-4, A-5, A-6 and A-7. It includes all materials containing 35 percent or less passing the No. 200 (75 μm) sieve which cannot be classified as A-1, A-3 or A-3a, due to fines content or plasticity (or both) in excess of the limitations for those groups.
Subgroups A-2-4 and A-2-5
This material consists of various granular materials containing 35 percent or less passing the No. 200 (75 μm) sieve and with a negative No. 40 (425 μm) portion having the characteristics of the A-4 and A-5 groups.
This material consists of materials such as gravel and coarse sand with silt contents of plasticity indexes in excess of the limitations of Group A-1, and fine sand with non-plastic silt content in excess of the limitations of Group A-3. A-2-5 soils are unsuitable embankment material under 703.l6.B because of its low weight, high optimum moisture, high LL, low PI, and its propensity to sloughing in service.
Subgroups A-2-6 and A-2-7
This material consists of materials similar to those described under Subgroups A‑2‑4 and A-2-5 except that the fine portion contains plastic clay having the characteristics of the A-6 or A-7 group. The approximate combined effects of plasticity indexes in excess of 10 and percentages passing the No. 200 (75 μm) sieve in excess of 15 are reflected by group index values of 0 to 4.
Group A-4
The typical material of this group is a non-plastic or moderately plastic silty soil usually having 75 percent or more passing No. 200 (75 μm) sieve. This group also includes mixtures of fine silty soil and up to 64 percent of sand and gravel retained on No. 200 (75 μm) sieve. The group index values range from 1 to 8, with increasing percentages of coarse material being reflected by decreasing group index values. The A-4 group soils are usually very difficult to compact or stabilize. Minimizing the water content to obtain the required density and stability usually works. It is not unusual, nor is it a change in condition, to have difficulty in stabilizing or compacting these soils. This condition should have been expected for this type of material.
Subgroup A-4a &A-4b
Subgroup A-4a contains less than 50 percent silt sizes. Subgroup A-4b contains more than 50 percent silt sizes. A-4b is only allowed 3.0 feet (1.0 m) below subgrade elevation because of frost heave potential. Both are susceptible to erosion.
Group A-5
The typical material of this group is similar to that described under Group A-4, except that it may be highly elastic as indicated by the high liquid limit. The group index values range from 1 to 12, with increasing values indicating the combined effect of increasing liquid limits and decreasing percentages of coarse material. This soil is unsuitable under 703.16.A for use as embankment material because of its elasticity.
Group A-6
The typical material of this group is a plastic clay soil usually having 75 percent or more passing the No. 200 (75 μm) sieve. The group includes also mixtures of fine clayey soil and up to 64 percent of sand and gravel retained on the No. 200 (75 μm) sieve. Materials of this group usually have high volume changes between wet and dry states. The group index values range from 1 to 16, with increasing values indicating the combined effect of increasing plasticity indexes and decreasing percentages of coarse material.
Subgroup A-6a & A-6b
Subgroup A-6a contains material with plasticity index of 15 or less. Subgroup A‑6b contains material with a minimum plasticity index of 16.
Group A-7
The typical material of this group is similar to that described under Group A-6, except that it has the high liquid limit characteristics of the A-5 group and may be elastic as well as subject to high volume change. The range of group index values is 1 to 20, with increasing values indicating the combined effect of increasing liquid limits and plasticity indexes and decreasing percentages of coarse material.
Subgroup A-7-5
Includes those materials with moderate plasticity indexes in relation to liquid limit and which may be highly elastic as well as subject to considerable volume change. This soil is unsuitable under 703.16.A because of its elasticity.
Subgroup A-7-6
Includes those materials with high plasticity indexes in relation to liquid limit and which are subject to extremely high volume change.
Slag Materials (203.02.Q)
Slags are by-products from manufacturing steel or iron. Under 203.02.Q, air-cooled blast furnace slag (ACBF), granulated slag (GS), open hearth (OH) slag, basic oxygen furnace (BOF) slag, and electric arc furnace (EAF) slag that meet the requirements in 703.16 are allowed under Item 203.
Air Cooled Blast Furnace Slag
Air Cooled Blast furnace slag is a by-product from making iron. It is a very hard and durable aggregate containing visible holes. ACBF slag may have maximum dry weight of about 80 lbs/ft3 (1280 kg/m3), and is lighter than most soils.
ACBF slag can produce a green, yellow, white, or black runoff; the color is usually pH driven. This runoff can also smell like rotten eggs, and usually goes away in about six months (but not always). The runoff may exceed the allowable limits under the Clean Water Act.
The potential for the runoff to exceed the Clean Water Act is based on the following factors:
1. The contaminate concentration of the ACBF slag.
2. The permeability of the ACBF slag.
3. The geometry of the in-place system. ACBF slag next to an underdrain has a higher potential than ACBF slag located in a fill surrounded by clay.
4. The amount of water flowing through the system.
5. Time of contact with the slag. Stagnant water around slag increases the potential for problems.
To minimize this problem in embankment construction, ACBF slag must pass the sulfur leachate test described in Supplemental Specification 1027. The manufacturers are required to certify that their material meets this requirement. Contact the District Testing Engineer or the Aggregate Section of the Office of Materials Management to verify that the material may be used.
Further details about the potential problems can be found in Other Wastes and Environmental Considerations in Section 202 “Regulated Waste Requirements” of this manual.
Granulated Slag
Granulated Slag (GS) is a by-product of making iron or steel. GS is a slag that has been quenched with water during the cooling process instead of air-cooling. Most of the granulated slags are iron slags. If steel slags are quenched with water they may cause explosions. Steel slag has about 20 to 25 percent iron in the slag while iron slag has less than one percent. It is a very light and brittle material, almost like powder in the pre-compaction condition. After compaction, it is very hard, durable, and almost impermeable. This material sets up like concrete in service. The maximum dry weight can range from 50 to 90 lbs/ft3.
Steel Slags
Steel slags are by-products of making steel. There are three kinds of steel slag defined in 203.02.Q: OH slag, BOF slag, and EAF slag. OH Slag is the slag that was produced mainly pre-1970. But some OH slag was made in the 1970’s. BOF and EAF slags are newer and faster processes for making steel. However, some BOF plants were in operation in the late 1950’s.
The problems associated with steel slags are worse for EAF and BOF slags than for OH slag. The process for making OH slag is slower than the other two materials. This slower process allows more of the harmful chemicals to be burnt out of the OH slag. Consequently, OH slag is a better product for embankment applications.
Some steel slags can expand, clog up underdrains, or have a high pH runoff. The specifications were written to minimize these problems. Similar to ACBF slag, the following factors were considered when writing the specification requirements:
1. The contaminate concentration (mainly MgO and CaO) of the steel slag.
2. The permeability of the steel slag.
3. The geometry of the in place system.
4. The amount of water flowing through the system.
5. Time of contact with the slag. Stagnant water around slag increases the potential for problems.
6. The load or weight on the material.
Further details can be found in Other Wastes and Environmental Considerations in Section 202 “Regulated Waste Requirements” of this manual. OH, BOF, and EAF slags may be used in embankment construction if the materials comply with Section 703.16.
Section 703.16 requires that OH, EAF, and BOF slag to be completely blended with natural soil or natural granular material. For OH slag, the blend must be at least 30 percent natural soil or natural granular materials. For BOF or EAF slags, the blend must be at least 50 percent natural soil or natural granular material.
The OH, EAF, and BOF slag must also comply with Section 703.15, which states that the aging, stockpiling, deleterious substances, and crushing requirements of 703.14 apply.
OH, EAF, and BOF slag and blends are further restricted in 203.03.E and 203.03.F. These materials must be at least 1.0 foot (0.3 m) below the underdrains to minimize underdrain clogging. These materials cannot be used underwater because of the potential pH problems.
All of the above restrictions minimize the factors that can lead to expansion, clogged underdrains, or high pH runoff problems.
Granular Embankment Material Types (703.16.C)
These materials replace the old granular embankment requirements under the 1997 specification book. The old requirements were too loose and just about any material could pass as granular material, even though it may not fit the engineering or designed need in the plans.
In 703.16.C, the following kinds of material are allowed: limestone (crushed carbonate stone or CCS), gravel, ACBF Slag, durable sandstone, durable siltstone, GS, or blended natural soil or granular materials with OH, BOF, EAF, or RPCC.
Durability requirements for sandstone and siltstone were previously covered in this manual under “Natural Granular Materials 203.02.H”. The slag requirements were also previously covered in “Slag Materials 203.02.Q” of this manual. RPCC will be covered later in this manual and must be blended similar to the slags. GS was covered earlier and is not required to have a specific gradation.
Six different gradations or types are available for use in construction. Below is a general description of these materials:
1. Type A Granular Material has less than 25 percent passing the No. 200 (75 µm) sieve.
a. Used as a general granular material with less fines.
b. Probably going to get sand most of the time. Sand is less expensive and widely available.
c. Gradation is too open for bridging soft areas in the subgrade.
d. Can be used to cover soft embankment foundations in thick lifts, such as in swamp treatment construction or with wick drains.
2. Type B Granular Material has the gradation of Items 304, 411, or 617, except 0 to 20 percent can pass the No. 200 (75 µm) sieve.
a. Well-graded and stable material.
b. Can be used to bridge soft subgrades or foundations.
c. Must be drained to be effective.
d. Unstable in the presence of free water.
3. Type C Granular Material has a top size of 3 inches (76 mm).
a. It is well graded.
b. Stable material and resistant to water influences.
c. Can bridge soft areas better than Type B.
d. Underdrains are difficult to construct through this material.
4. Type D Granular Material has a top size of 8 inches (200 mm).
a. It is well graded.
b. Stable material and resistant to water influences.
c. Can bridge soft areas better than Type B or Type C.
d. Underdrains cannot be constructed through this material.
e.
Consider placing geotextile fabric or 304 to prevent piping.
(See Figures 203.J and 203.K)
5. Type E Granular Materials are very free draining and open materials.
a. Coarse aggregates from No. l through 67 are used.
b. Used to bridge areas that cannot be drained.
c. Surround with geotextile (712.09, Type D) or Type B or C Granular Material to prevent piping. (See Figures 203.J and 203.K)
6. Type F Granular Material has general requirements only:
a. Well graded material.
b. Top size from 8 to 3 inches (76 mm) with a bottom size of No. 200 (75 µm) sieve.
c. Evenly graded material between the top and bottom sizes.
d. Compactable, stable, and serves the intended use.
e. Almost never specified.
f. Can mainly be used to accept materials that do not meet the specific Type A thru E requirements.
Figure 203.J – Fine Material Migration
Figure 203.K – Preventing Piping
Rock (203. 02.O)
The following rock description is in the specifications: “Sandstone, limestone, dolomite, glacial boulders, brick, and RPCC too large to be placed in an 8-inch (200 mm) loose lift.” The construction of rock fills are different than the construction of soil or shale fills; therefore, it is important to clearly identify them in the field.
Rock Identification
It is important to understand the differences in these materials and to have a basic understanding or their origins.
Almost all rock in the state of Ohio is sedimentary rock. Sedimentary rock is formed by cementation, precipitation from solutions, or by consolidation.
Sandstone is a deposition of sand from rivers, wind, or oceans. This material was cemented together under earth pressure or consolidation. Coarse sandstone can be readily identified by the sand grains in the field. Fine-grained sandstone can be confused with siltstone or limestone.
Limestone is calcite formed from ocean deposits of sea organisms (seashells) that were cemented chemically and or by pressure. Chert is similar to limestone but it consists of silica minerals rather than calcite. Dolomite is limestone with magnesium and calcium carbonate.
Limestone or Dolomite can be readily identified by using a solution of diluted hydrochloric acid. When hydrochloric acid is dropped on the limestone or dolomite the acid will fizz or bubble. The amount of fizzing depends on how much calcium is in the rock. A pure dolomite may not fizz unless the fines of the rock are tested.
Rock boulders are materials brought from Canada during the glaciers and can consist of just about any stone. The amount of earth pressure or chemical crystallization greatly influences the hardness of the stone.
Almost all rock will have a ringing sound with a rock hammer. However, some punky or loosely cemented rock will not ring.
Shale (203.02.P)
By the specification shale is defined as “Laminated material with a finely stratified structure formed by the natural consolidation of soil. For the purpose of this specification, the following bed types are also considered as shale: mudstone, claystone, siltstone, and clay bedrock.”
The way we evaluate shale in the field has changed from earlier versions of the specification. In the past, shale was identified and compacted “as directed by the Engineer”. The new approach gives the Engineer a systematic approach to evaluate the shale to ensure long-term durability of the shale fill. It enables the Engineer to identify these materials and to distinguish between durable, nondurable, soft, and hard shale.
Shale Identification (703.16.D)
Shale is a sedimentary material that consists of silt or clay particles. Shale was formed when earth pressure squeezed water out of silt and clay mud. In short, shale is consolidated mud. In addition, some shale may be crystallized or cemented together into a stone like form.
The following procedure is detailed in 703.16.D. Shale is evaluated for durability and hardness as follows:
Obtain a typical 6-inch (150 mm) diameter piece of shale.
1. If it cannot be obtained because the material is too weak, weathered, or deteriorated, then the shale is soft shale.
2. Place the shale in a bucket of water. Examine the deterioration or slaking after 48 hours.
3. If the material has not deteriorated, then try to break the shale down by hand pressure. If 75 percent or less of the material is retained on the ¾-inch sieve, then the shale is soft shale. Otherwise, use a roller to perform a field test for hardness.
4. Field test for hardness as follows:
a. Use a roller with a minimum compression of 500 pounds per linear inch (57 kN/mm) of roller drum width.
i. Roller centrifugal force divided by the roller width.
ii. The Contractor must provide verification of the force.
b. Make six complete passes. Visually determine the amount of shale that breaks down.
i. If the percentage of shale that breaks down is more than 40 then material is soft shale
ii. If the percentage of shale that breaks down is 40 or less then material is a hard shale
Different materials will always be mixed together in a fill situation. However, this hardness or durability test will give the project a good indication of how the material should break down during compaction. It also provides a ready means to determine the test method to use for compaction acceptance. The following is a summary.
1. If less than 25 percent is retained on the ¾-inch (19 mm) sieve, then test and break down like soil.
2. If 25 to 75 percent is retained on the ¾-inch (19 mm) sieve, then break down to granular material size and compaction test the same as granular material.
3. When greater than 75 percent is retained on the ¾-inch (19 mm) sieve, use field test for hardness.
a. If more than 40 percent breaks down under roller, then break down and test like granular material.
b. If less than 40 percent breaks down under roller, then it is a hard durable shale. Treat it like rock and use roller passes per C&MS 203.06.
Further descriptions are detailed in Supplement 1015 “Compaction Testing of Unbound Materials” in this manual.
The following table, based on color alone, can be used for the expected general condition of shale:
|
Color |
Expected Shale Condition |
|
Red |
always soft non-durable |
|
Green |
1/3 Soft non-durable 1/3 Hard non-durable 1/3 Hard durable |
|
Grey |
1/3 Soft non-durable 2/3 Hard non-durable |
|
Black |
1/2 Soft non-durable 1/2 Hard non-durable |
Of course, this should never be used as acceptance criteria. These numbers will change depending the project location and geologic formation.
Random Materials (203.03.L)
By definition, random materials are: “Mixtures of suitable materials that can be placed in 8-inch (200 mm) loose lifts.”
Other Allowed Materials under 703.16 and 203.02
Asphalt Concrete (203.02.A & 703.16)
Recycled asphalt concrete is allowed if the material is less than 4 inches and is blended with at least 30 percent natural soil or natural granular material. The mixing and maximum size requirements are used to minimize the effects of water on the asphalt consistency. Place a piece of asphalt in a bucket of water and see what happens.
In addition, this material is restricted in 203.03.A & B.
Portland Cement Concrete (203.02.M & 703.16)
Recycled Portland Cement Concrete is allowed if the material is blended with at least 30 percent natural soil or natural granular material. Additional mixing requirements are in 203.06.D when used as random material. This material is further restricted in 203.03.B, E &F. This material can clog underdrains and produce a lime rich high pH runoff similar to steel slags as discussed earlier.
Petroleum Contaminated Soil (203.02.K & 203.03.J)
The use of Petroleum Contaminated Soil (PCS) is regulated by law. The legal contamination level of this material is listed in 203.03.J.
This material is usually found around underground storage tanks. The level of contamination is so low that you may not be able to see or smell the petroleum in the soil.
Section 203.03.J requires that an environmental consultant review the proposed use and test the material. Submit the report to the Chemical Section in the Office of Materials Management for approval.
Coal (703.16)
Coal is a very lightweight material and is not very durable. It is allowed in natural embankment materials when it comprises less than 10 percent of the blend. It is impossible to keep this material out of the fill on large earthwork construction projects.
Recycled Materials (203.02.N, 203.02.R & SS-871)
The specifications define recycled materials as fly ash, bottom ash, foundry sand, recycled glass, tire shreds, or other materials or manufacturing by-products not specifically named as suitable materials in 203.02.R.
The construction and acceptance details are in Supplemental Specification 871. These materials may have levels of contamination that must be controlled and are regulated by law. Like all other materials ODOT uses, these materials are restricted and have certain engineering properties that must be accounted for in the specifications.
A general discussion of the specification is in Section 202, “Regulated Waste Requirements” of this manual. All supplemental specifications can be found on the Division of Construction Management’s webpage on the Department’s website.
The specification requires environmental and geotechnical approval. Submit the environmental report to the Chemical Section in the Office of Materials Management for approval. The geotechnical report and materials acceptance is approved by the Office of Geotechnical Engineering.
Figure 203.L is a typical application of recycled materials. These materials are used in the inner core of the embankment structure. This controls the chemicals leachate and minimizes the detrimental engineering properties.
Figure 203.L – Typical Cross-Section for Recycled Materials
Figure 203.M details what can go wrong if one uses a recycled material in the wrong fashion. Read the article and be careful. Further discussion about the recycled material is beyond the scope of this manual.
Figure 203.M - Tire Fire
Figure 203.M – Tire Fire (continued)
Restrictions (203.03)
Section 203.03 lists materials restricted by the specifications. These restrictions ensure that the embankment structural integrity is sound in the short and long term. Keep in mind that what seems to be a good product in the field may have serious long-term consequences once in place. Many of these restrictions were detailed in the previous sections in this manual.
Many embankment materials are allowed in several locations throughout the embankment structure. These allowable material types are further restricted in the top 2 to 3 feet of the embankment to ensure long-term structural integrity of the pavement.
Some of the general reasons for these restrictions are:
1. Water accumulates under the pavement and deteriorates the material.
2. Frost causes some materials to heave and break down to smaller pieces.
3. The load or stress at this location is higher.
General Construction (203.04)
This section details general information about earthwork construction. No explanation is needed for most of this section except for the following subsections.
Drainage and Maintenance of the Work (203.04.A)
It is vital to the embankment for the Contractor to maintain a well-drained construction operation. Contractor’s can provide proper drainage without an enormous effort.
Here is some relevant text from the specifications.
“Maintain a well drained embankment and excavation operation. … Construct the embankment with sufficient cross-slope to drain in case of rain.”
Maintained cross slopes ensure that the rain runs off the embankment construction area instead of filtering into the embankment. It is difficult to remove water once it is in the embankment. Further embankment construction is compromised once the existing embankment is saturated.
Using a saturated embankment as a haul road can destroy the embankment structure and density. The following sentences are from the specification.
“If precipitation saturates the embankment construction, stay off the embankment construction until the embankment dries or stabilizes. Expedite the construction by removing the saturated embankment or dry the embankment by scarifying, plowing, disking, and re-compacting the embankment.”
The specifications continue to give the project significant leverage to use with the following passage.
“Throughout the embankment construction operation and at the end of each day’s operation, shape to drain, compact, and re-compact the work area to a uniform cross-section. Eliminate all ruts and low spots that could hold water.
If using embankment construction or cut areas to haul on, continuously move the hauling equipment around on the area to take advantage of the compactive effort. Continually re-grade and compact the haul roads and maintain the construction according to 105.12 and 105.14.”
Contractors will use a multitude of excuses to avoid maintaining a well-drained embankment area. Some of them are legitimate and some are not. The project will have to use common sense in evaluating them.
Staged Construction (203.04.G)
Plans will often have fill restrictions that mandate the monitoring of the fill height. The plans may call for limiting the fill construction to 3 to 5 feet a week, and may require waiting periods of 30 to 90 days.
In any case, these restrictions usually mean that the embankment will be constructed on a soft foundation. By limiting the load, it allows the foundation to consolidate slowly and allows the pore pressure to dissipate so that the embankment does not fail.
In many cases, it is required that the project monitor the fill height, pore water pressure, and settlement versus time. Figure 203.N shows such a plot.
Figure 203.N – Settlement Plot
On the horizontal axis is a plot of time, usually plotted in weeks. There are three simultaneous plots on the vertical scale.
Settlement is plotted on the lower half of the drawing. The majority of plans will call for a certain percentage of consolidation or a number of days. The number of days can be waived if a certain percentage of consolidation is achieved.
A best-fit line is drawn between points A and B once the settlement is plotted. This line is then extrapolated to point C, which is the anticipated flattening point of the curve.
As an example, ODOT is asked to estimate the consolidation in week 5. The total settlement that has occurred to the 5th week is 2.5 feet. By extrapolation, the settlement is predicted to stop at 3.0 feet. Therefore the consolidation is 2.5/3.0 = 83 percent. If the required consolidation is 95 percent then more readings are required.
The designer should always give the consolidation percentage to construction personnel.
Pore water pressure and fill height may be monitored in some cases. In Figure 203.N, the fill height is 25 feet and was completed in week 3. If the pore pressure is in excess of the fill height, then stability is probably going to be a problem.
The project engineer should obtain the maximum pore water pressure from design prior to the beginning of the project. Notice in Figure 203.N that the pore pressure dissipated from week 4 to week 5.
Embankment Construction Methods (203.05)
Foundation of Embankments
If you recall from Section 201.04, scalping is not required if the fill height is greater than 9 feet (3 m) and the existing slope is 8:1 or flatter. Both conditions must apply for the areas to be left un-scalped. Figure 203.O shows the conditions when scalping is required and when it is not.
Figure 203.O – Scalping Requirements
There is a minimum compaction requirement for all foundations that require scalping. The compaction requirement is 95 percent of standard proctor or 95 percent of the test section maximum value. This minimum value is easily achieved. An alternate method may need considered if density cannot be achieved.
Soft Foundations
Foundation conditions are occasionally encountered that require treatment to obtain stability either within or beyond what is proposed in the contract documents. These soft foundation conditions do not take into account the long term settlement potential. The following details are to allow the project to correctly construct the embankment in order to ensure a stable embankment. There are two general conditions detailed below:
1. Moderately Soft Foundation.
a. Low lying poorly drained areas with high moistures.
b. Soil unstable due to extreme high moistures.
c. Equipment rutting less than 12 inches (0.3 m).
d. Elastic or pronounced elastic movement.
e. All of the above are constructible with moderate changes.
2. Severely Soft Foundation
a. Peat deposits.
b. Swampy areas that contain organic soil with high moisture.
c. Underwater conditions.
d. Buried Equipment.
e. Un-constructible with soil replacement.
The nature and degree of the foundation instability will vary considerably.
Moderately Soft Foundation
The first step in determining the proper treatment for a soft foundation and ensuring embankment stability is to determine and consider the following:
1. Planned embankment height above the foundation.
2. Allowed construction time frame.
3. Nature of the foundation material.
a. Water content.
b. Location of free water.
c. Location of possible outlets for drainage.
d. Extent in depth and area of unstable material.
4. Type of embankment material.
The following types of corrective measures have been successfully used for many years. Measures required to correct unstable foundations often are apparent when the cause and extent of the instability are known. The following sections consider three different moderately soft conditions that can occur during construction:
Embankment Heights Greater than 12 feet (4 m)
The higher the fill height above the foundation, the better chance the project has in bridging over soft foundation locations with very little additional expense.
Section 203.05 allows the Engineer to increase the lift thickness to bridge soft foundation locations. The specifications refer to areas that do not support the weight of the trucks or hauling equipment (areas with less than 12 inches (305 mm) of rutting or a moderately soft foundation). For areas with more than 12 feet (4 m) of fill, this method should be the first alternative utilized.
Section 203.05 allows the following technique when placing material over the soft foundation:
1. Dump successive loads of material in a uniform lift.
2. Do not exceed the lift thickness required to support the equipment placing the material.
3. Manipulate, blade, distribute, level, and doze the material until the area is stabilized.
4. Once the bridging has been accomplished, construct the remaining lifts according to 203.06.
This is standard practice in soft foundation locations. Density controls during this initial construction are not required. If the soft foundation is just wet and does not have standing water, then soil dryer than optimum may be used.
If the foundation has standing water, consider placing construction underdrains or ditches to drain the soft areas (if the area can be drained). If the areas cannot be drained then use rock, granular material, or hard durable shale in 1 to 3 foot lifts (0.3 to 1 m).
Observe the embankment stability once the bridging material is in place, and make adjustments as required. Reevaluate the conditions when the embankment is 6 feet (2 m) below grade.
Embankment Heights Less than 12 feet (4 m) but more than 6 feet
Investigate the source of the problem. Evaluating foundation conditions is similar to evaluating the condition of a subgrade. Before determining the solution, first evaluate the foundation conditions by digging test pits, evaluating the soil borings and observing the rut depth.
Use the section “The Investigation” under Item 204 of this manual, Figure 204.G Subgrade Test Pit Investigation and Figure 204.H Subgrade Treatment Chart to help evaluate the foundation.
Determine the average N, average U, and rut depth values using the above sections. Evaluating soft subgrade and soft foundations is similar with a slight variation. If the soft material is less than 2 feet (0.6 m) in depth, remove it and replace with soil.
If the average U > 0.5 tons/ft2, average N > 5, and the rut depth is less than 6 inches (150 mm), then use an initial lift of soil that is about 1 to 3 feet (0.3 to 1 m) thick. The soil should be less than optimum moisture.
Do not use soil to bridge areas with standing water or in conditions where some embankment has already been placed as in the previous section.
If the soil conditions are worse than these values or the rut depth is more than 6 inches (150 mm), then use an initial lift thickness of 1 to 3 feet (0.3 to 1 m) of rock, granular material, or hard durable shale.
Drain the soft foundation by using construction underdrains or ditches, if the slope allows the area to be drained. Continue to evaluate the conditions when constructing the remaining fill, and adjust when required according to the next section.
Embankment Heights Less than 6 feet (2 m)
If the source of the problem has not been previously evaluated, then investigate the source of the problem as detailed in the previous section.
Determine the average N, average U, and rut depth values. Again, evaluating soft subgrade and soft foundations are similar with slight variations.
To determine the correct fix, use the Subgrade Treatment Chart in Figure 204.H and find the correct undercut depth or stabilization depth.
Subtract the fill height from the recommended undercut depth to determine the required undercut depth in the foundation. See Figure 203.P
Figure 203.P – Fill Undercut Depth
Example
Given:
New Construction Project
2 feet (0.6 m) of fill
U=0.5 tons/ft2, N=5 and Ruts > 6 inches (150 mm)
From
Figure 204.H Subgrade Treatment Chart,
recommended undercut depth = 3 feet (1 m)
Solution:
Required undercut is 1 foot and place 3 feet (1.0 m) of Granular Material for the fill. As an alternative, consider stabilizing the foundation with cement or lime and then placing 2 feet (0.6 m) of stabilized soil.
Severely Soft Foundations
Severely soft foundations are conditions that cannot be constructed without using rock or granular material. These conditions usually are in standing water or even underwater. Construction equipment either gets buried in the areas or cannot operate in these locations. Peat deposits or swampy areas that contain organic soil with high moisture are the norm in these locations.
Unless these areas are called out in the plans, it is best to contact the District Geotechnical Engineer or the Office of Geotechnical Engineering to evaluate the depth and extent of the required undercut.
This section examines two different methods to remove and replace this soft material.
1. Total Excavation Method
2. Partial Excavation and Displacement Method
There will be plan notes associated with these methods. The following is a brief description of the methods of construction of these two.
Total Excavation Method
Below is a cross-sectional view of the total excavation method. This method, as the name implies, is used to where all of the soft material can be removed down to a firm foundation.
Figure 203.Q – Cross-Section View of a Total Excavation
The excavation and backfilling progresses across the soft foundation for depths up to 20 feet (6 m) deep or the reach of the track hoe. Below is a plan view of the same operation. The filling progresses at the same time as the excavation.
Figure 203.R – Plan View of the Filling and Excavation
Many times the excavation is performed on the same side, the embankment side, as the filling but this takes some coordination by the Contractor. Below is the longitudinal view of the same operation. The filling operation normally keeps the fill at least a foot (0.3 m) above the soft material of water level.
Figure 203.S – Longitudinal View of the Total Excavation
Partial Excavation and Displacement Method
At times it is economical to only remove portions of the soft foundation. The cross-section view is shown below.
Figure 203.T – Partial Depth Removal
Below is a longitudinal view of the partial depth operation. A surcharge of material is required to displace the soft material forward as much as possible. The work needs to progress across the soft foundation such that soft material does not get entrapped in the replacement material. This is true for either full or partial depth replacement.
Figure 203.U – Longitudinal View of Partial Depth
In these operations, the plan will denote which method of excavation it to be used for the work. In the past, the volume of the work was very difficult to quantify. A new plan note has been developed to simplify this measurement. The designer will choose the type of replacement material to be used to replace the soft foundation material. Use a table similar to the one below to convert the weight of the replacement material to volume.
Table 203.A – Conversion Factors for Replacement Materials
|
Granular Materials |
Dumped Rock Fill |
||
|
Type |
Tons/Cubic Yard |
Type |
Tons/Cubic Yard |
|
A B C D E |
1.6 1.9 1.8 1.8 1.6 |
A B C D |
1.9 1.9 1.8 1.7 |
The replacement material may be granular material or dumped rock fill. Prior to the material being dumped into the soft foundation, weight tickets are taken to finalize the replacement quantities estimated in the plans.
After the quantities for the replacement materials in tons are known, then this quantity is converted to cubic yards using the above table. This cubic yardage is used to determine the quantity of excavation to be paid. This simplifies the measurement of the material that normally cannot be measured directly in the field.
Materials
The material used for this operation may be granular material or rock fill types. Usually Granular Material Type C or D is used for these conditions. Dumped Rock is usually specified for depths greater than 10 feet (3.3 m). The project should check the potential for piping. See Figures 203.J and 203.K.
Disposal of Material
The unsuitable excavated material may be temporarily left in place or used for flattening adjacent slopes outside the plan lines. This material must be either shaped into the final slope or disposed of 2 weeks prior to paving the project.
Consolidation Method
There is another method to bridge a soft foundation. It is the consolidation method. It was mentioned in Section 203.04.G. It is beyond the scope of this manual but a typical cross-section is presented below.
Figure 203.V – Consolidation Method
A layer of sand is placed to bridge over the soft foundation usually around 3 feet thick. Wick drains are then placed through the foundation soils. These wick drains allow the pore pressure to dissipate faster as the fill is constructed.
Benching
Beginning with the 2002 C&MS, the language was more explicit than in the previous versions of C&MS. This new language was put in C&MS to ensure that benching is properly performed in the field. Figure 203.W details where benching is required. Benching is required for all embankments placed on or against a slope steeper than 8:1. Of course, the existing slope has to be scalped first. This applies on all embankment areas whether the existing embankment cross slope is in the transverse or the longitudinal direction.
Figure 203.W – Benching Required
Figure 203.X details the bench into the existing embankment. For side hill fills, the existing embankment is physically notched out and connected to the new embankment. Benching requires horizontal cuts in the existing slope.
Figure 203.X – Benching
The bench needs to be wide enough to blend the new embankment with the existing embankment. In Figure 203.Y, the total width between point A and B must be the width of the dozer blade and the compaction equipment.
Figure 203.Y – Benching in New Embankment
If the plan calls for a new embankment, or the distance between C and B is less than a blade width or about 8 feet, then the existing embankment must be benched in the difference or a of distance A and C.
In Figure 203.Z, the horizontal distance between points D and E is about 4 feet (1.3 m). Therefore, the existing embankment must be benched into for about 4 more feet (1.3 m) to complete the bench.
Figure 203.Z – Sliver Fills
Bench into the slope as the embankment is placed, and compact into layers. Begin each bench at the intersection of the existing slope and the vertical cut of the previous bench. The re-compaction of the cut materials is required.
Benching is nothing more than a side hill foundation. Benching knits two embankments together to ensure that a failure plane does not occur. Figure 203.AA details typical benching seen on some plans.
Figure 203.AA – Typical Benching
In this case, the designer anticipated that there was a stability problem or weak soils in the existing embankment (or both). This is called special benching.
Side hill embankments present unique problems in that they may be stable when originally constructed yet become unstable later. The result is usually a landslide.
If the bench is not benched into the existing embankment far enough then a weak plane can develop as shown in Figure 203.BB. A failure may occur along this weak plane and the bench material will move laterally. The project should evaluate the existing soil conditions and determine if more benching is required than shown on the plans or required by the specifications.
Figure 203.BB – Benching Problems
Bench Drainage
In many cases, the main cause of an embankment benching failure is water related. Seeping water into the embankment from the side hill or foundation can cause considerable instability in the existing and the new embankment. Water is an elusive quantity to capture during the design phase because of many factors. Notice in Figure 203.BB how water can move into the bench material and weaken the bench material.
Special attention must be given to side hill embankments. Consult the plans and soil profile to see where special benching, if any, is required; to see whether or not spring drains are provided, and to see if any potential spring or wet zones are mentioned. The areas should be inspected in detail for possible springs. In dry seasons, green or lush vegetation are often indicative of a semi-dormant spring that may become active during prolonged periods of precipitation. If spring zones are encountered and no spring drains are provided in the plans, then drains should be added to the work.
If there is any indication of water, then drainage should be added if it is not detailed in the contract. The following pages detail some typical solutions to use in the field.
Spring drains are detailed on the plans by plan note D109 and on the second sheet of Standard Drawing DM 1.1. Plan note D109 can be found in Location & Design Manual – Volume 2, Drainage Design. Links to the Location & Design Manuals and the standard drawings can be found on the Design Reference Resource Center on the Department’s website.
The standard drawing is partially shown in Figure 203.CC. The standard drawing does not call for it but it is recommended to use non-perforated pipe outside the #57 stone and perforated inside the #57 stone. Wrap or coil the pipe inside the #57 stone for maximum efficiency. Completely wrap the #57 stone with Type A geotextile fabric. In many cases #8 stone can be substituted for the #57 stone without sacrificing much drainage capacity and it also reduces the risk of piping. The application of a spring drain is for local wet spots.
Figure 203.CC – Spring Drains
Severe Bench Drainage Problems
Drainage always should be added when the benching embankment is placed next to a rock or shale cut. In this case, add drainage along the entire length and width of the shale/rock benching interface. Experience has shown that water always leaches from this interface. In addition, if a large quantity of water is coming into the bench or water is leaching from several locations and elevations then drainage should be added across the entire bench face. In both examples above a different approach needs to be taken because of the severity of the water issue. There are two potential solutions to the severe drainage problems.
Adding Drainage when Benching from the Top Down
If the slide repair benching plan has 1 to 1 back slopes and consists of minimum 10 foot wide and high benches and the slope can be excavated from the top of the cut all the way to the bottom then the following drainage should be considered.
The use of geotextile fabric and #8 stone as detailed in Figure 203.DD to take the water flow is one solution to solve the drainage issue. The geotextile is used to stop the migration of fines into the #8 stone. Notice that the geotextile fabric is used on both sides of the #8 stone to prevent migration from either side.
Figure 203.DD – Severe Water Problems in a Bench
The geotextile fabric that is generally used is 712.09 Type A geotextile. The drainage aggregate can be number #8, #9 or #89 size. The drainage pipe going into the page is a 6-inch Item 605, 707.33 perforated pipe. The lateral drain is a 6-inch Item 603 Conduit Type F non-perforated. This lateral drain backfill should be surrounded by at least 12 inches (300 mm) of sand. This will provide a secondary outlet if the pipe gets clogged.
Figure 203.EE – Multiple Bench Layout
These benches can be interconnected and outlet as detailed in Figure 203.EE. Section A is the #8 stone and the geotextile fabric. Section B is the non-perforated pipe with an outlet to Section F. Notice that the bench and the pipe are outletted using a one percent grade or 100:1 slope. This ensures that the water can effectively be removed from the system without leaching into the soil mass.
Figure 203.FF – Detail for outlet F
Figure 203.FF details the outlet configuration. The balloon number 2 is a 20 mil plastic to prevent the water from entering the soil along the slope. Balloon number one above details 712.09 Type D geotextile fabric that serves to protect the plastic from getting torn during the rock installation. The balloon 3 details the Rock Channel Protection. In this case the rock type was Type C. This rock type should be used in most cases.
Figure 203.GG – Lower Bench Outletting
Figure 203.GG details the lower benching. In the above slide repair, the lower embankment was existing and did not require reconstruction. But the lower benches needed to be drained. The bench and pipe drainage into the page of the cross-section was sloped at a one percent grade. The slope of the outlet E from left to right is sloped at a one percent grade. The outlet pipe excavation was about 20 feet deep. This is a high risk operation during construction. This construction can be done without trench boxes or laying back the slope if necessary. The trench is excavated in maximum 50-foot lengths. The pipe is jointed together above ground and dropped into the hole. Grade is kept by conventional methods or by GPS. In this case, sand is dumped in the trench up to an elevation 580. The sand should be hoe rammed in place in thick lifts. Compaction requirements are secondary in this case to the ability to keep the trench from collapsing. Keep the open trench as small as possible and no personnel are to enter the trench during these operations.
Figure 203.HH – Detail for Slope Protection G
After the outlet is constructed, the outer slope will be sand for about 6 feet wide. Detail G in Figure 203.HH, details the erosion protection required. A 712.09 Type D geotextile is placed under Type C Rock Channel Protection. The width of the material should be the width of the sand.
Figure 203.II – Top View of the Drainage
Figure 203.II details the plan view of the drainage pattern in the slide repair. You will notice that the outlets are spaced at 200 feet intervals and that the benches are sloped at a one percent grade toward them. Notice that the high point on the bench is 100 feet from the outlets and goes in both directions toward the outlets.
When the benching cannot be performed from the top down or the benches are small another method of adding drainage to the benching plan needs to be considered. Figure 203.JJ, shows adding a 20 foot drainage trench to drain an upper unstable slope(to the left) and to prevent the embankment from becoming saturated. The drainage into the page is sloped at a one percent grade.
Figure 203.JJ – Using Trenching and Sand
Since this trench is around 20 feet deep it is a high risk operation during construction. This construction can be done without trench boxes or laying back the slope if necessary. The trench is excavated in maximum 50 feet lengths. By keeping the trench length to a small interval it minimizes the potential for collapse or upper slope damage. The pipe is jointed together above ground and dropped into the hole. Grade is kept by conventional methods or by GPS. Sand is dumped in the trench up to about 3 feet below ground level. The sand should be hoe rammed in place in thick lifts. Compaction requirements are secondary in this case to the ability to keep the trench from collapsing.
In Figure 203.KK below, the above trenching technique is expanded to drain the entire counter berm. The drainage at the toe is provided by the rock fill while the three trench drains to the left drain at third point intervals along the existing new fill interface. The center two sand drains are placed at the interface of the existing ground and the new embankment. The construction of the middle two sand drains is slightly different than the other sand drain but only slightly. The embankment is constructed to the top elevation of the sand trench. Then the sand trench, pipe and outlets are constructed as previously described.
The sand that is generally used for these operations is asphalt, concrete or masonry sand. There is a possibility that the soil will pipe into the sand or the soil will clog the sand. The possibility of this happening is considered a small risk and is beyond the scope of this manual.
In Figure 203.JJ, the pipe in section B is perforated and wrapped with geotextile fabric to prevent the sand from piping in the pipe.
Figure 203.KK – Multiple Benching with Sand
Figure 203.LL details the plan view of the drainage system. It is basically the same as detailed previously. The outlets are spaced at every 200 feet and everything drains at a one percent slope.
Figure 203.LL – Plan View of Drainage
Spreading and Compacting (203.06)
This section covers a general description of spreading and compacting materials. A more detailed explanation can be found in Section 1015 “Compaction Testing of Unbound Materials”.
The procedures outlined in this section will make or break the quality of the earthwork construction. Control over the lift thickness and compaction of the materials is vital to the success of the project.
Certain materials require compaction at thinner lifts than others to obtain their maximum strength. Other materials can be compacted in thicker lifts without sacrificing quality. Some materials require the addition of water to help in the compaction effort or to help break down the material, while other materials require mixing to get the desired results.
All embankment materials, except for rock in 203.06.C. and RPCC in 203.06.D, are spread in horizontal loose lifts not exceeding 8 inches (200 mm). All embankment material lifts, except for rock and hard, durable shale, are compacted to a specified density and moisture requirements in 203.07.
The material is spread using dump trucks, scrapers, and dozers. In general, a sheepsfoot or tamping foot roller is used to compact rock, shale, clay, and silt material. Granular materials are generally compacted using a smooth drum vibratory roller.
To record the embankment construction operations an inspection sheet was created to help document the work. The CA-EW-12 Daily Earthwork Inspection Sheet is required to be filled out for all filling operations according to Supplement 1015. There are several sections to check off on the form that denote project information, location of the work, type of equipment used and embankment operation information. With this form, it should make it easier for the earthwork inspector to determine what the minimum inspection requirements are during the earthwork operations.
The four methods used for compaction acceptance are proctor testing, test section method, aggregate correction method, and roller pass method.
Soil and Granular Embankment (203.06.A)
Use a maximum lift thickness of 8 inches (200 mm) for soil and granular embankment. Soil compaction acceptance is based on the proctor testing, test section method, or aggregate correction method. Granular material compaction acceptance is based on the test section method.
These methods are covered in the “Compaction Testing of Unbound Materials” Section 1015 of this manual.
Shale (203.06.B)
Shale is consolidated mud. Shale may seem hard but in many instances it can be broken down to soil size with very little effort. See 203.02.P and 703.16.D in this manual for a full description of the material.
Some hard, durable shale can be excavated or blasted in very large sizes. Contractors control the size of the material by the way they blast the material. During the typical rock blasting operation, the bench height/burden (L/B) ratio is greater than one, the production hole spacing (S) is 10 to 15 feet (3.3 to 5 m), and the production hole diameter (D) is 6 inches (150 mm). These dimensions are typical in order to maximize production. In addition, it generally leaves large chunks of rock or shale. These large pieces are fine for rock fills but are not conducive to shale fills.
To produce smaller shale or rock fragmentation, the blaster can increase the L/B to about 3, decrease S to 6 to 8 feet, and reduce the D to about 4 inches (100 mm). These dimensions are changed in a trial and error method. The most efficient method depends on the shale and rock formations.
If the Contractor does not control the material size during the excavation or blasting, then the amount of spreading, manipulation, compacting and watering will be extensive to get the material in 8-inch (200 mm) lifts.
All shale material is placed and compacted in 8-inch (200 mm) lifts. If the material is placed and compacted in thicker lifts then a situation such as in Figure 203.MM can happen. Loose and non-durable shale intermixed within the lift can deteriorate later when water runs though the system.
Figure 203.MM – Thick Lift of Shale
In many cases, when thick lifts are used, the compaction in the top 8 inches (200 mm) may pass. If the top 8 inches (200 mm) is removed, the lower material is made of loose and large chunks of soft shale.
Figure 203.NN details what happens when shale is not properly placed and broken down. The embankment load on the shale along with the water going through the embankment causes the soft shale to break down.
Figure 203.NN – Inadequate Shale Compaction and Breakdown
In order to ensure long-term durability, the project needs to determine how much to break the shale down in the field. The amount of breakage during construction is directly related to the durability and hardness of the shale. The hardness and durability are correlated to the bucket test and roller pass methods in the specifications.
The specifications require that the shale be tested for compaction and broken down according to the bucket test and the subsequent roller pass evaluation.
A summary of this evaluation follows:
1. Perform initial test for hardness in 703.16.D (Bucket Test).
2. Consult the following:
a. If less than 25% retained on ¾-inch sieve then shale should be broken down to soil size.
b. If 25% to 75% retained on ¾-inch sieve then, an even percentage of soil, small-, and coarse-sized shale is obtained (maximum contact with all particles). Shale should have a granular texture when properly broken down in the field (see Figure 203.OO).
c. If more than 75% retained on ¾-inch sieve then field test for hardness (703.16.D).
3. Use six passes with rollers specified in 703.16 to field test for hardness.
4. Consult the following:
a. If greater than 40% breaks down then break material into a granular texture as detailed in Figure 203.OO.
b. If 40% or less breaks down then use the procedure in Section 203.06.B in C&MS (Hard Durable Shale): 10 passes with a 15-ton roller, and fill the voids.
Figure 203.OO – Granular Texture Shale
The above procedure is a systematic approach to evaluating potential shale breakage in the field. In practice, field results will vary because of variability of shale and the mixing of different types of shale and rock. Some judgment is required by the project during construction.
The most important factors in the long-term quality of shale fills are:
1. Water shale until the material is at least 2 percent above optimum moisture throughout the lift.
2. Manipulate or mix by dozing until a maximum 8-inch (200 mm) loose lift is achieved. Remove large chunks of shale or rock that exceed this lift thickness.
3. Compact each lift to a maximum density, except for hard durable shale. Use 10 passes with a 15 ton roller in 203.06.B for hard durable shale.
4. Typically about 5 to 10 passes are sufficient for shale compaction.
Rock (203.06.C)
Maximum loose lifts are as follows:
1. Six inches larger than the largest rock piece with a maximum lift thickness of 3 feet (1 m). Some examples follow for clarification.
a. The maximum rock size in a 3 foot lift is 2.5 feet.
b. If the largest rock size in a lift is 1 foot then the maximum lift thickness is 1.5 feet.
2.
Near Bridges, within a length of 6 times the height of the fill at the
abutment. Use less than 18-inch (0.5 m) lifts.
Example: Fill height is 20 feet (6 m), so within 120 feet of abutment.
(20 × 6 = 120 feet)
The rock fill construction is outlined below:
1. Distribute full width of the lift.
2. Evenly distribute the larger rocks.
3. Reduce the voids.
4. Place the smaller rock in the upper portion of the lift.
5. Compact with 8 passes of a 10 ton (9 metric ton) roller.
When using other embankment materials with rock, use rock as:
1. Base of the embankment. It provides better support.
2. On the outer portions of the embankment. It provides better drainage.
3. Place the larger rocks on the outside side slopes. It provides better drainage.
Use other embankment material as follows:
1. On the inner portion of the fill.
2. Keep the top higher than the rock.
3. Construct wide enough for compaction.
4. When rock is on top of other embankment material, construct at a side slope grade of 4 percent prior to placing the rock. This provides better drainage.
When the rock fill contains more than 15 percent shale, then compact like a shale fill.
Random Material (203.06.D)
Random materials are a wide variety of materials which do not fit any other groupings. They may be rock mixed with soil, brick, asphalt mixed with soil, or Portland cement concrete mixed with soil.
Soil mixed with any other random material must be at least 2 percent below optimum. This will help fill the voids and create a stable embankment.
Recycled asphalt or concrete are mixed with at least 30 percent natural materials.
Random material mixtures are placed in 8-inch lifts, except for RPCC:
1. Maximum size of the RPCC is less than 3 × 3 feet (1 m).
2. The mix is dozed and mixed to fill the voids.
3. Lift thickness is less than 12 inches (300 mm).
4. Use 18-inch lifts (0.5 m) when the lift is more than 50 percent RPCC.
5. Compact the natural material to a test section maximum.
Compaction and Moisture Requirements (203.07)
Except for granular material types D and E, rock and hard, durable shale, the moisture and density controls in this section apply. The Department will perform all compaction tests according to Supplement 1015. This supplement is detailed in Section 1015 “Compaction Testing of Unbound Materials” of this manual.
Moisture Controls (203.07.A)
Water is added or subtracted to a condition to obtain the density and stability. Dry or add moisture throughout the lift. Expedite and manipulate the material by using plows or discs. For soils with pronounced elasticity or deformation, reduce the moisture content to ensure stability.
In a fill situation without a soft foundation, heavy equipment may deflect the soil but no permanent rutting or cracking should be evident afterwards.
Some soils require moisture contents 5 percent below optimum to ensure stability. Materials such as A-4a, A-4b, and A6a’s are notorious for this problem. These materials are difficult to compact during marginal weather conditions and just after a rainy day.
The elasticity may be caused by foundation conditions. See Materials 203.02, “Elasticity and Deformation of Soils” in this manual.
Do not mix shale in the lifts to reduce the moisture content. The shale will bring the moisture down then break down later causing settlement or a landslide.
Compaction Requirements (203.07.B)
Table 203.07-1 details the “Embankment Compaction Requirements”. The percentage is based on the maximum dry weight of the soil. This table is used for materials tested using proctor testing or aggregate correction testing methods.
Table 203.07-1 – Embankment Compaction Requirements
|
Max. Dry Weight (lb/ft3) |
Minimum Percent Compaction |
|
90 to 104.9 |
102 |
|
105 to 119.9 |
100 |
|
120 and more |
98 |
Test sections are required for granular materials and other materials. If test section results are used then the following apply:
1. Use at least 98 percent of the maximum value obtained in the test section for acceptance in the production area.
2. Use the same number of passes used in the test section for the production areas. Reduce the number of passes if detrimental to the compaction.
3. Construct a new test section when the material or supporting foundation changes.
4. Reduce the moisture content if the material becomes unstable.
More detail is in Supplement 1015 “Compaction Testing of Unbound Materials” in this manual.
Method of Measurement (203.09)
This section of the manual is intended to give a brief outline of some of the methods to determine earthwork quantities. Methods described in this section are acceptable for making this check. Many of these methods are outdated because of GPS systems but they are still presented.
Specification Requirements
The specifications require that the average-end-area method be used to determine volumes of earthwork for payment.
End Area Determinations
There are many acceptable methods for determining end areas for earthwork computations. Any method that gives accurate determinations may be used. Some of the most common methods for determining cross-section end areas are as follows:
Planimeter
In this method, an instrument with a wheel and a graduated dial is run around the perimeter of a cross-sectional end area. The area is found by multiplying the reading on the dial by a constant factor or by setting a factor on the planimeter and by reading the area directly from the planimeter dial.
Counting Squares
In this method, the number of unit squares in a section is counted. This is not practical except for very small sections.
Stripping
This is a method of tallying unit squares by making successive marks on a strip of paper to measure unit strips, accumulating all unit strips on a cross-section, and converting to total cross-section area. This method is simple and rapid and keeps the chance of error to a minimum.
Computer Method
In this method, data from cross-sections (usually in coordinate form) is input into a computer program, which follows a program setup to finish areas and volumes.
CAD
Most plans are developed using computer aided design (CAD) programs. In these files, the earthwork calculations are detailed. Contact Production for these calculations.
Geometric Method
In this method, the section is broken into areas, such as triangles and trapezoids. Each area is then calculated by its geometry. The total area is found by summing the individual areas.
Arithmetic Calculation
This method calculates end area using a formula. Data for the formula is taken from a cross-section (or field notes) showing elevation and distance from a base line for each break in the cross-section line. A pocket calculator can be used for this calculation.
Determination of cross-section end areas by this method is exact and any two persons using the same information (field notes) will obtain the same answer, providing no errors are made in the calculator manipulation or arithmetic calculations. There is only one correct answer.
The two methods are described and illustrated in Figures 203.PP and 203.QQ.
Figure 203.PP – End Area Determination Method 1
Figure 203.PP-M – End Area Determination Method 1 (Metric)
Figure 203.QQ – End Area Determination Method 2
Figure 203.QQ-M – End Area Determination Method 2 (Metric)
Volume Determination
The end areas of English plans are detailed in square feet (ft2), while end areas on metric plans are detailed in square meters (m2). Make the appropriate volume calculation shown below using the end area found in Figure 203.PP or 203.QQ.
Formula
For base lines and center lines on tangent, and for center lines on curves where the center line of the curve coincides with the center of mass (centroid) of the cross-sections, the formula for computing volume from end areas are as follows:
English Units
Where
V = volume in cubic yards (yd3)
A1 = cross-section one end area in square feet (ft2)
A2 = cross-section of other end area in square feet (ft2)
L = distance between A1 and A2 in feet (ft)
Metric Units
Where
V = volume in cubic meters (m3)
A1 = cross-section one end area in square meters (m2)
A2 = cross-section of other end area in square meters (m2)
L = distance between A1 and A2 in meters (m)
Table
Figure 203.RR shows a table for use in determining cubic yards (yd3) from the sum of end areas for sections 100 ft. apart, and for conditions described above. This table cannot be used on metric projects.
Figure 203.RR – Cubic Yards for the Sum of the End Areas
Earthwork Quantity Calculations
Figure 203.SS Earthwork Calculations depicts a form that can be used to summarize the earthwork calculations.
Figure 203.SS – Earthwork Quantity Calculations Form
Figure 203.TT shows a completed calculation form.
Figure 203.TT – Completed Earthwork Quantity Calculations Form
Volume Determination on Curves
Where cross-sections are at right angles to curve center lines, and the center line is not located at the center of mass (centroid) of the cross-sections, corrections must be applied to volume calculations to obtain an accurate result. This is especially true for curves of short radius, such as those commonly used on ramps. Inaccuracies of considerable magnitude may result unless proper corrections have been used in calculating earthwork volumes. General methods for determining accurate quantities in such cases are detailed in Section 1310.3.2 and Figure 1310-1 in the Location & Design Manual – Volume 3, Highway Plans. Links to the Location & Design Manual can be found on the Design Reference Resource Center on the Department’s website.
Basis of Payment (203.10)
There are a multitude of statements that denote when the Department will and will not pay for earthwork quantities based on different field circumstances. The project should review this section. In this manual, we will focus on the final quantity measurements.
The GPS methods are not detailed in Section 203.09 or 203.10 of this manual. Electronic devices connected to graders or dozers are allowed in Item 623 in Section 623.02 of the C&MS.
Final Earthwork Quantities
Check measurements are made in areas where earthwork is being performed. A sufficient number of these checks must be recorded according to the instructions in this manual to provide a satisfactory record of the checks. The purpose of these measurements and records are:
1. To ensure that earthwork is being constructed to plan lines within specified tolerances.
2. To provide a simplified method of earthwork measurement so that payment may be based on corrected plan quantities.
This will result in the savings of engineering man-hours required to arrive at payment quantities and make it possible for the Contractor to receive prompt final payment after the completion of the work.
Measurement by Final Cross-Sections
Final cross-sections of roadway earthwork are usually ‘not’ required provided that the plan quantities are checked for accuracy and adequate checks have been made (and recorded) during construction. This establishes that plan quantities of earthwork have been performed within specified tolerances.
Final cross-sections may be called for by the Office of Construction where, by inspection or other knowledge of the project, it is indicated that measurement by final cross-section is necessary or desirable.
Procedure for Check Measurements and Check Calculations:
1. Before earthwork construction has begun, make a plan-in-hand inspection to verify the ground line shown on the plan cross-sections, and if significant changes in topography indicate the need for additional cross-sections at intermediate locations. Where this inspection indicates the need, arrange for further checks by ground or aerial survey.
2. State in the project diary that this inspection has been made.
3. Ensure that slope stakes are set by the calculation method. The initial point for calculations should generally be a profile grade elevation.
4. Obtain a copy of the survey notes, whether the staking is done by a Department or Contractor survey crew, and plot horizontal and vertical locations of the slope stakes on the cross-section sheets. Check the accuracy of original plan ground cross-sections at slope stake locations. Record errors noted and correct plan sections promptly.
5. Check the accuracy of the original ground lines shown on plan cross-sections as follows:
a. In order to verify the original ground lines shown on plan cross-sections, the Engineer shall field check cross-sections every 300 to 500 feet (100 to 150 meters) by either ground or aerial survey methods prior to the beginning of construction operations. If any appreciable variations from plan elevations are found, check sections must be taken at closer intervals in order to determine the extent of plan errors and amount of additional cross-sectioning required to provide accurate earthwork quantities. Use the corrected ground line where plan cross-section lines have been found in error.
b. Plan quantities resulting from computations that have been properly documented and made a part of the project records are to be used as final pay quantities. Any additions to, or deductions from, plan quantities necessitated by change orders shall be computed by project personnel in order to determine final pay quantities for adjusted items.
c. The Department will make revisions to the pay quantity for changes for the following:
i. Total contract changes greater than $5000.
ii. Two consecutive end areas varying by more than 5 percent.
iii. Undercutting.
iv. Foundation settlement.
v. Changes in the grades or slopes.
vi. Removing slides.
vii. Arithmetic errors.
d. Final pay quantities computed or adjusted by project personnel shall be checked, in the project office of the District office, by competent Department personnel who have been assigned to the project for construction control, supervision, etc.
e. All computations of adjustments shall be properly validated by the signed initials or names of persons who computed the adjusted pay quantities and those who performed the checking operations. Also, the dates that these functions were performed shall be indicated. These adjustment computations shall be made a part of the official project records.
6. Where the plan quantities have been checked and validated on the plans, or on computation sheets provided by the design unit preparing the plans, it is not necessary during construction to make a detailed check of accuracy of plan earthwork quantities. If an error in validated plan quantities is noted, recalculate the end areas and volumes in question. Check all plan earthwork quantities for accuracy when plan quantities have not been checked and validated on the plans or on computation sheets provided by the design unit preparing the plans. Especially check locations where there are curves of short radius, such as ramps. Plan quantities are frequently in error by significant amounts at such locations. Where plan quantities are not correct, strike out the plan figures and write in the correct figures. Check the summary to see that quantities have been transferred accurately from cross-section sheets.
7. Make check measurements during construction to ensure work is being done within allowable field tolerances. Project personnel should perform these checks, supplemented by occasional use of the Department survey crew when needed. Make sufficient checks to ensure that the work is being performed within allowable tolerances. The frequency of these check measurements should be determined by the Engineer.
8. The Contractor is required to correct all deviations from plan lines in excess of allowable tolerances as determined by check measurements. During rough grading, it is acceptable to permit cuts and fills to exceed tolerances by an amount which will be corrected during fine grading by practical construction methods. In the case of fills, require prompt corrections of deviations inside allowable tolerances so that specified compaction of the outer edges will be obtained as the work progresses. In the case of deep cuts with steep slopes in rock or shale, prompt correction of deviations in excess of allowable tolerances is required, so that adjustments can be made as the work progresses while the slope areas in question are within reach of the equipment being used.
9. Record necessary check measurements in appropriate notebooks, inspectors report forms, or daily entry in the project diary. These notations should state the location where check measurements were made.
10. Maintain a set of plan cross-sections in the project office. Plot check measurements, changes, and errors in plan lines on these plans on all projects where there is authorized work beyond plan lines, such as excavation of soft subgrade in cut, measurements of this authorized additional work are required.
Borrow Pay Quantity
Specifying borrow happens rarely and only when the measurement in the final location is impractical. An example would be underwater or linear grading operations. Borrow will be specified by weight, when practical.
Natural Formations
Volume Measurement
When borrow is specified by the cubic yard, measurement may be taken in the borrow pit just as in regular embankment construction. Use the average end areas.
Only use Department personnel to make all measurements of the borrow material. Contractor's employees may be used to assist in check measurements and measurements of authorized excavations beyond plan lines where the quantity at each location is less than 2,000 cubic yards (yd3) [1500 cubic meters (m3)]. This assumes that project personnel only are responsible for collecting, plotting, and calculating of the data and quantities.
Weight Measurement
When borrow is specified by cubic yard, weight measurements may be used to calculate the payment quantity:
1. Take a series of density tests in the borrow areas, and average the test results. This value is the wet density, called WD (lbs/yd3).
2. Calculate the total weight from the weight tickets. This value is called W (lbs).
3. Use the following equation to calculate the payment quantity.
This can be used as a check or if cross-sections are not available.
Other than Natural Formations
Volume Measurement
1. Take a series of density tests in place, and average the test results. This value is the wet density, called WD (lbs/yd3).
2. Calculate the total weight from the weight tickets. This value is called W (lbs).
3. Use the following equation to calculate the payment quantity:
Weight Measurement for Borrow
When borrow is specified by weight use the following:
1. Weight tickets minus excess moisture.
2. Collect weight tickets according to C&MS 109.01.
Adjustment to Borrow Quantity
The quantity of borrow for payment is the measured quantity as detailed above minus:
1. Suitable excavation wasted.
2. Excess fill adjusted for shrinkage.
a. The shrinkage factor used is detailed in Section 203.02 “Estimating Shrinkage and Settlement” of this manual.
b. Use the following equation to calculate the payment quantity:
Payment Quantity = SF × Borrow Quantity
Example 100,000 CY total borrow, 10,000 CY excess, borrow density is 110 lbs/ft3 and embankment density 120 lbs/ft3.
Solution:
Shrinkage Factor, SF=110/120= 0.92
100,000 - 0.92 (10,000) = 100,000 – 9,200= 90,800 CY
Explanation:
Borrow was measured at the borrow site. A larger amount of borrow fit into the embankment. Density is greater at the embankment location. Therefore, we subtract less borrow from the final pay.
Be careful about which way you apply the shrinkage factor.
Records
Record all check measurements and check calculations on the appropriate form, date and sign or initial the form, and place it in the project records.
Records of check measurements must be kept up-to-date at the project office during construction and will be reviewed by the Office of Construction during their routine visits to the project.
After completion of the earthwork, prepare a tabulation of earthwork pay items showing plan quantities where applicable, and listing appropriate measured quantities for all areas where there was deviation from plan lines beyond specified tolerances which affect the pay quantities, showing total quantities for payment.
This tabulation, together with records of check measurements, constitutes the earthwork report for the project. After processing, these reports shall be filed in the District Office.
Documentation Requirements - 203 Roadway Excavation and Embankment
1. Materials.
2. Verify plan cross-sections.
3. Cross-sections of borrow site, if required.
4. Classify suspect soils.
5. Foundation.
6. Lifts thickness and roller passes.
7. Equipment used.
8. Type of soils.
9. Take compaction tests according to S-1015.
10. Benching.
11. Verify final cross-sections.
12. Base estimate on yardage from cross-sections, load count or electronic grade control data.
13. Measure and Pay according to 203.09 and 203.10
14. Document on CA-EW-1, CA-EW-12 and CA-D-3. Do not duplicate the information on all forms unless necessary.