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, include 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 that 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 five 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 would be evaluated by the traveling public as a rough job or a poorly constructed project. No notice or credit would be given to 95 percent of the work that was constructed properly. The entire project might be discredited and be considered poor because a small proportion of the project was constructed with poor earthwork construction procedures or practices.
The foregoing 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 from the beginning to the end of earthwork 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 cannot be overemphasized. The results of improper construction practices may or may not show up during construction. However, 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:
A geotechnical engineer ensures that the embankment will be stable as designed. The pavement is constructed on top of the embankment.
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.
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.
A factor of safety is the ratio of the resisting forces divided by the driving forces, as shown in the following equation.
Typically the minimum factors of safety for embankment structures are from 1.3 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.
Proper excavation techniques in cut sections are just as important as embankment construction. The only difference is that when it fails, 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 onto the roadway as illustrated in 203.E-1. This figure shows a deep-seated wedge failure. This failure can also occur in an embankment 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 onto the 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.
In the 2002 version of the specification, the definitions and material requirements were changed for the different types 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.
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.
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 grained 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 dry density of at least 90 pounds per cubic foot (1450 kg/m3). Materials that are less than this density 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.
These materials are defined in 203.02.H as follows: “Natural granular materials include broken or crushed rock, gravel, sand, durable siltstone, and durable sandstone that can be placed in an 8 inch (200 mm) loose lift.”
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 grained 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
It is sometimes necessary to make field decisions based on very little (if any) laboratory soils information. 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 are some, but certainly not all, of the methods that can be used to identify these materials in the field.
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. 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.
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. Refer to properties of soils in the next section.
A clay material can be easily rolled into a thread at a moisture content 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. As the clay content increases, the thread may be easier to roll into smaller sizes. No matter what the soil content is you cannot roll a pure silt material into a 1/4 inch (6 mm) thread.
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. Wet clay dries much slower than silt.
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 clay. A silt material is easily removed when hands are 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 aforementioned 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.
The following are general statements regarding the engineering properties of soil and granular materials. Consider these properties when solving field problems.
Granular soils are less affected by moisture content than clays and silts; have larger voids; and are free draining. Granular materials have relatively larger particles than silts and clays.
Moisture content (also called 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 moisture 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). The liquid limit and plastic limit are the moisture contents at the condition of the test.
The following is a brief description of the characteristics of soils in the physical states.
Each term used in geotechnical engineering has specific meaning and application. Each soil test has specific meaning and application and indicates certain soil properties. Using correct terminology will prevent confusion and misunderstanding.
Soils have properties that influence their behavior and value. The properties of soil will vary with gradation (composition), moisture content, vertical position in relation to the surface of the ground, and geographical location. The more common properties encountered and used in highway work are defined and discussed in Section 203.
Most soils were originally 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-sized particles can be made, then silt-sized particles, and finally clay-sized particles. Chemical changes take place as nature reduces rock into finer particles; therefore, clay produced by nature over a period of many years will vary from clay-sized material produced in a short time in a laboratory.
By naming and defining the size of 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 to judge, analyze, and classify 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, which uses a hydrometer to determine the necessary data.
Size definitions used by the Department are the same as definitions used by AASHTO T-88 with the exception of clay:
Larger than 12 inches (300 mm)
3 to 12 inches (75 to 300 mm)
ľ to 3 inches (19 to 75 mm)
#10 sieve to ľ inch (2 to 19 mm)
#40 sieve to #10 sieve (0.42 to 2.0 mm)
#200 sieve to #40 sieve (0.074 to 0.42 mm)
0.005 to 0.074 mm
Smaller than 0.005 mm
The amount of each soil type (i.e., boulders, cobbles, silt, and clay) contained in a soil mixture determines its texture or feel. Soil classifications by texture must not be confused with soil classifications for engineering purposes. Sometimes these classifications are similar, but other times they may be different. The amount of each soil type in a soil mixture is determined by laboratory tests. The test results are then compared with texture definitions in order to determine 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 tells a lot about the soil. Using texture classification, approximations and estimations can be made of soil properties, such as bearing value, water-holding capacity, probability to frost heave, permeability, etc.
It is the practice of the Department to describe soil components and texture of a soil as follows:
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.
Descriptions of secondary components are preceded by the term listed below, according to the percent of total sample indicated:
Percent of Total Sample
0 to 10
10 to 20
20 to 35
35 to 50
Examples of material texture descriptions based on component test results are as follows:
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 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 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. 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 firmly together. This will give the soil such high cohesion that a hammer may be required to break the particles apart. These conditions are illustrated 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.
The stability and 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 of 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. This soil is produced by high internal friction due to sand and gravel and high cohesion due to clay. Clay illustrates a soil of low bearing value. 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 is defined as the action by which a liquid (water) rises in a channel above the horizontal plane 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 rises above the water table and will range from 0 in some sand and gravel to as high as 30 feet (9 meters) or more in some clay soils. It often requires a long period of time for water to rise to 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.
Complete saturation of soil seldom occurs at the upper limits of rise in 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 determines whether frost heave and similar occurrences in subgrade will create a problem requiring treatment for satisfactory performance in service.
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.
Soil elasticity measurement is determined by special tests that simulate moisture changes and loading conditions anticipated in the field.
When heavy rubber-tire construction equipment moves over an embankment layer foundation of wet, fine-grained soil, some movement of the embankment surface occurs. Elastic movement occurs when a 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.
Cracking may occur in cases of pronounced elasticity. In the case of pronounced elasticity or deformation, there is displacement of surface soil to each side of the tire, which results in deformation, rupture, cracking, and rutting.
The magnitude of the elastic movement or deformation may depend on one or more factors:
Some embankment elasticity and deformation is expected under construction equipment loading. Moderate movement of less than a 1/2 inch (13 mm) can occur with heavy equipment weighing 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 weighing 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 made 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. 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 to observe stability.
When the Engineer or Inspector questions or desires to check the stability of an area during embankment construction, they are authorized to require that the Contractor moves 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 refers to the apparent decrease in volume of a soil during its removal from the cut or borrow and its placement in the embankment. Shrinkage is caused by a greater density in the fill than in the cut or borrow area. 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 one 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.
Losses due to scalping are usually insignificant as a percentage of the overall embankment construction quantities. Scalping losses of around 6 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, it can be accounted for by taking cross-sections and then 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 platforms, 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.
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 regarding the length of influence of individual or multiple settlement platforms.
Example of total settlement:
543.11 - 542.88 = 0.23 feet
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. Permeability depends on the size and number of soil pores as well as 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 factors such as void ratio, particle size and distribution, structure, and degree of saturation. The permeability of a particular soil will vary with the degree of compaction since this will influence the size of soil pores. A particular soil, loosely packed, will be more permeable then the same soil tightly packed. Nature produces these differences along 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.
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 10-3 (0.001). For earth dams, the U.S. Bureau of Reclamation classifies soil with k values approximately 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.
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-4318 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.
The liquid limit (LL) is the moisture content at which a soil passes from a plastic to a liquid state. The test, ASTM D-4318 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 1/2-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 types of clay 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.
The plasticity index (PI) is defined as the numerical difference between liquid limit and plastic limit. Calculation details are included in ASTM D-4318 or 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 (NP).
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).
The following is a brief description of the materials in each classification group detailed in Figure 203.G.
The typical material of this group is a well-graded mixture of gravel stone fragments, 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.
This material predominantly consists of stone fragments or gravel, either with or without a well-graded soil binder.
This material predominantly consists of coarse sand with or without a well-graded soil binder.
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.
This material consists of mixtures of coarse and fine sand with limited amounts of low plasticity silt.
This material consists of a wide variety of granular materials which 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.
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 which have 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 703.16.B because of its low weight, high optimum moisture, high LL, low PI, and its propensity to sloughing in service.
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 which has 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.
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 be expected for this type of material.
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.
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.
The typical material of this group is a plastic clay soil which has 75 percent or more passing the No. 200 (75 μm) sieve. The group includes 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 contains material with plasticity index of 15 or less. Subgroup A‑6b contains material with a minimum plasticity index of 16.
The typical material of this group is similar to that described under Group A-6, except that it has the high liquid limit characteristics similar to that of group A-5, 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 that indicate the combined effect of increasing liquid limits and plasticity indexes and decreasing percentages of coarse material.
Includes those materials with moderate plasticity indexes in relation to liquid limit and may be highly elastic as well as subject to considerable volume change. This soil is unsuitable under 703.16.A because of its elasticity.
Includes those materials with high plasticity indexes in relation to liquid limit and are subject to extremely high volume change.
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 is a by-product from making iron. It is a very hard and durable aggregate, which contains visible holes. ACBF slag may have a maximum dry density of approximately 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 smell like rotten eggs and usually goes away in 6 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:
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 (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 1 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 density can range from 50 to 90 lbs/ft3.
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; however, 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:
Further details can be found in Other Wastes and Environmental Considerations in Section 202 Regulated Waste Requirements. 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 be 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 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.
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 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 previously covered 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:
The following rock description is in the specifications: “Sandstone, siltstone, limestone, dolomite, glacial boulders, brick, and RPCC too large to be placed in an 8-inch (200 mm) loose lift.” Rock fills are constructed differently than the construction of soil or shale fills; therefore, it is important to clearly identify them in the field.
It is important to understand the differences in these materials and to have a basic understanding of 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.
According to the specification, shale is defined as “A fine-grained sedimentary rock formed from the lithification of clay, silt, or mud. Shale has a laminated structure, which splits easily (is fissile). For the purpose of this specification, mudstone and claystone are also considered to be shale.” Laminated means that it is made up of thin layers or sheets. Fissile means that the layers are easily split apart.
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 current 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 and nondurable shale.
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. Some shale may be crystallized or cemented together into a stone like form.
Shale is evaluated for durability as described below. The procedure is detailed in C&MS 703.16.D. It is commonly called the Bucket Test.
1. Obtain a piece of shale that is typical and representative of the rest of the shale. The size of the piece should be about 6 inches (150 mm). If a 6-inch (150 mm) sample is not available, then the shale is nondurable.
2. Place the piece of shale in a bucket of water. Examine the deterioration or slaking of the shale after 48 hours. If the shale has deteriorated, then the shale is nondurable.
3. If the shale has not deteriorated after being in water for 48 hours, then break down the shale over a 3/4-inch (19.0 mm) sieve by hand pressure. If 75 percent or less of the shale is retained on the 3/4-inch (19.0 mm), then the shale is nondurable.
4. If more than 75 percent of the shale is retained on the 3/4-inch (19.0 mm) sieve or, then perform a field test for durability. The field test for durability consists of compacting the shale with six passes of a steel drum roller which has a minimum compaction force of 500 pounds per lineal inch (57 kN/mm) of roller drum width. Ask the contractor for documentation to verify the roller meets the compaction force requirement.
a. If more than 40 percent of the shale breaks down, by visual inspection, then the shale is nondurable.
b. If less than 40 percent of the shale breaks down, by visual inspection, then the shale is durable.
Different materials will always be mixed together in a fill situation. However, the durability test will give you 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 compaction testing procedure for shale is described in Supplement 1015, Compaction Testing of Unbound Materials, but it is also summarized below.
The color of the shale can be a good indication of the durability of the shale. Red shale in Ohio is always nondurable, while grey, green, and black shale is generally, but not always, nondurable. Most durable shale in Ohio is grey or green. Of course, the color of the shale is just a general guideline, and should never be used as the sole criteria for durability. The durability of shale will change depending on the project location and geologic formation.
By definition, random materials are “Mixtures of suitable materials that can be placed in 8-inch (200 mm) loose lifts.”
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.
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.
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 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.
The specifications define recycled materials as fly ash, bottom ash, foundry sand, recycled glass, tire shreds, 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 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.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.
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:
This section details general information about earthwork construction. No explanation is needed for most of this section except for the following subsections.
It is vital to the embankment for the Contractor to maintain a well-drained construction operation. Contractors 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 recompacting 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 recompact 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 105.13 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.
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. Limiting the load 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 days. The vertical axis shows both settlement and the fill height. You can obtain a spreadsheet that will generate the settlement plot from the Office of Geotechnical Engineering.
The plans will usually specify a settlement waiting period. This is an estimate by the designer as to how long the settlement will take. However, the actual amount of time it takes for the foundation to settle under the new embankment load is dependent on the actual site conditions, and may be either more or less than the estimate shown in the plans. The standard plan note says that the Project Engineer may adjust the waiting period based on the settlement readings. As a general guideline, the settlement is usually considered complete when the settlement readings result in 1/8 inch or less of settlement over a week of time. The Contractor must include the plan specified waiting period in the construction schedule. If the waiting period ends up being shorter, then the Contractor can proceed ahead of schedule. If the waiting period ends up being longer, then the Contractor may be eligible for a time extension due to an excusable delay under C&MS 108.06.
The plans may also require monitoring of the pore water pressure in some cases. When the pore pressure readings exceed some threshold, the Contractor will have to suspend embankment construction until the pore pressures dissipate. The plan notes will give the pore pressure threshold, when to take baseline readings, and minimum reading schedule.
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.
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 to be considered if density cannot be achieved.
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:
The nature and degree of the foundation instability will vary considerably.
The first step in determining the proper treatment for a soft foundation and ensuring embankment stability is to determine and consider the following:
The following types of corrective measures have been used successfully 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.
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:
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.
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.
If the slope allows the area to be drained, drain the soft foundation by using construction underdrains or ditches. Continue to evaluate the conditions when constructing the remaining fill and adjust when required.
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.
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)
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 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:
There will be plan notes associated with these methods. The following is a brief description of the construction methods of these two.
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.
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.
Many times the excavation is performed on the same side as the filling, the embankment side, 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 1 foot (0.3 m) above the soft material of water level.
At times it is economical to only remove portions of the soft foundation. The cross-section view is shown below.
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.
In these operations, the plan will denote which method of excavation is 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 that will 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
Dumped Rock Fill
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, the 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.
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.
The unsuitable excavated material may temporarily be left in place or used for flattening adjacent slopes outside the plan lines. This material must either be shaped into the final slope or disposed of 2 weeks prior to paving the project.
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.
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.
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 to all embankment areas whether the existing embankment cross-slope is in the transverse or the longitudinal direction.
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.
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.
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, which is the distance from A to 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 about 4 more feet (1.3 m) to complete the bench.
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.
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; they may be stable when originally constructed, yet become unstable later. The result is usually a landslide.
If the bench is not benched far enough into the existing embankment, 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 is shown on the plans or required by the specifications.
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. Due to many factors, water is an elusive quantity to capture during the design phase. Notice in Figure 203.BB how water can move into the bench material and weaken it.
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, drainage should be added if it is not already detailed in the contract. The following pages detail typical solutions to use in the field.
Spring drains are detailed on the plan 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 web site.
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 No. 57 stone and perforated inside the No. 57 stone. Wrap or coil the pipe inside the No. 57 stone for maximum efficiency. Completely wrap the No. 57 stone with Type A geotextile fabric. In many cases No. 8 stone can be substituted for the No. 57 stone without sacrificing much drainage capacity and it also reduces the risk of piping. The application of a spring drain is used for local wet spots.
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. If a large quantity of water is coming into the bench, or water is leaching from several locations and elevations, drainage should be added across the entire bench face. In both examples above, a different approach needs to be taken due to the severity of the water issue. There are two potential solutions to the severe drainage problems.
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 No. 8 stone to take the water flow, as detailed in Figure 203.DD, is one solution to solve the drainage issue. The geotextile is used to stop the migration of fines into the No. 8 stone. Notice that the geotextile fabric is used on both sides of the No. 8 stone to prevent migration from either side.
The geotextile fabric generally used is 712.09 Type A geotextile. The drainage aggregate can be No. 8, No. 9, or No. 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 611, 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.
These benches can be interconnected and outlet as detailed in Figure 203.EE. Section A is the No. 8 stone and the geotextile fabric. Section B is the non-perforated pipe with an outlet into Section F. Notice that the bench and the pipe are outlet 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 details the outlet configuration. Balloon number two is a 20 mil plastic to prevent the water from entering the soil along the slope. Balloon number one details 712.09, Type D geotextile fabric, which serves to protect plastic from getting torn during rock installation. Balloon number three 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 preexisting and did not require reconstruction, but the lower benches did need 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. If necessary, this construction can be done without trench boxes or laying back the slope. 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. In this case, compaction requirements are secondary to the ability of keeping the trench from collapsing. Keep the open trench as small as possible and no personnel are to enter the trench during these operations.
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 details the plan view of the drainage pattern in the slide repair. You will notice that the outlets are spaced at 200-foot intervals and 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.
Since this trench is around 20 feet deep it is a high risk operation during construction. If necessary, this construction can be done without trench boxes or laying back the slope. 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 approximately 3 feet below ground level. The sand should be hoe rammed in place in thick lifts. Compaction requirements are secondary to the ability of keeping 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 and 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.LL details the plan view of the drainage system, which is similar to that previously detailed. The outlets are spaced every 200 feet and everything drains at a one percent slope.
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 in order 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 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 durable shale, are compacted to a specified density and moisture requirement in 203.07.
The material is spread using dump trucks, scrapers, and dozers. In general, a footed drum 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 Form. 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. This form should make it easier for the earthwork inspector to determine what the minimum inspection requirements are during the earthwork operations.
Use a maximum lift thickness of 8 inches (200 mm) for soil and granular embankment. Compaction acceptance for soil is based on a percentage of maximum dry density. The appropriate maximum dry density value is determined from a one-point Proctor test, one-point Proctor test with aggregate correction, or a test section. Compaction acceptance for granular material is also based a percentage of maximum dry density, but the maximum dry density value is always determined from a test section.
These methods for determining the maximum dry density are covered in Section 1015, Compaction Testing of Unbound Materials, of this manual.
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 ratio to about 3, decrease S to 6 to 8 feet, and reduce 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, the amount of spreading, manipulation, compacting, and watering will be extensive in order to get the material into 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 occur. Loose, nondurable shale, intermixed within the lift can later deteriorate when water runs though the material.
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, can cause the nondurable shale to break down.
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 of the shale. The durability is 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:
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 during construction.
The most important factors in the long-term quality of shale fills are:
Maximum loose lifts are as follows:
The rock fill construction is outlined below:
When using other embankment materials with rock, use rock as:
Use other embankment material as follows:
When the rock fill contains more than 15 percent shale, compact like a shale fill.
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:
Except for granular material types D and E, rock, and durable shale, the moisture and density controls in this section apply. Perform all compaction tests according to Supplement 1015. This supplement is detailed in Section 1015 Compaction Testing of Unbound Materials.
Water is added or removed from a material in order to obtain the necessary density and stability. Note: for embankment material, there is no explicit range of acceptable moisture content (e.g. within 3 percent of optimum moisture content). The criteria for acceptable moisture content are that the Contractor can obtain the necessary 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 directly after a rainy day.
The elasticity may be caused by foundation conditions. See Materials 203.02, Elasticity and Deformation of Soils.
Do not mix shale in the lifts to reduce the moisture content. The shale will bring the moisture down, and then break down later causing settlement or a landslide.
Table 203.07-1 details the Embankment Compaction Requirements. The percentage is based on the maximum dry density of the soil. This table is used for materials where the maximum dry density is determined using a one-point Proctor test or a one-point Proctor test with aggregate correction.
Table 203.B – Embankment Compaction Requirements
Maximum Dry Density (lb/ft3)
Minimum Compaction Requirements in Percent of Maximum Dry Density
90 to 104.9
105 to 119.9
120 and more
Test sections are required to determine the maximum dry density for granular materials and some other materials. If a test section is used then the following apply:
More detail can be found in Supplement 1015 Compaction Testing of Unbound Materials.
This section of the manual briefly outlines some of the methods used to determine earthwork quantities. Methods described in this section are acceptable for making this check. Many of these methods are outdated due to current GPS (GNSS) systems, but they are still presented.
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:
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 reading the area directly from the planimeter dial.
In this method, the number of unit squares in a section is counted. This is only practical in very small sections.
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, rapid, and keeps the chance of error to a minimum.
In this method, data from cross-sections (usually in coordinate form) is input into a computer program, which follows a program set-up to finish areas and volumes.
Most plans are developed using Computer Aided Design (CAD) programs. The earthwork calculations are detailed in these files. Contact Production for these calculations.
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 the sum of the individual areas.
This method calculates end area using a formula. Data for the formula is taken from a cross-section (or field notes) that show 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.
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.
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:
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)
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)
Figure 203.RR shows a table used for determining cubic yards (yd3) from the sum of end areas for sections 100 feet apart and for conditions described above. This table cannot be used on metric projects.
Figure 203.SS Earthwork Calculations depicts a form that can be used to summarize the earthwork calculations.
Figure 203.TT shows a completed calculation form.
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 cross-sections, corrections must be applied to volume calculations in order to obtain accurate results. This is especially true for curves of short radius’s, 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.
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 (GNSS) 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 of the C&MS.
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:
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.
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 where, by inspection or other knowledge of the project, it is indicated that measurement by final cross-section is necessary or desirable.
Total quantity changes greater than 1,000 cubic yards.
Two consecutive end areas varying by more than 5 percent.
Changes in the grades or slopes.
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.
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 take 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) [1,500 cubic meters (m3)]. This assumes that project personnel only are responsible for collecting, plotting, and calculating of the data and quantities.
When borrow is specified by cubic yards, weight measurements may be used to calculate the payment quantity:
This can be used as a check or if cross-sections are not available.
When borrow is specified by weight use the following:
The quantity of borrow for payment is the measured quantity as detailed above minus:
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
Shrinkage Factor, SF=110/120= 0.92
100,000 - 0.92 (10,000) = 100,000 – 9,200= 90,800 CY
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.
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 Administration 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.
Verify plan cross-sections.
Cross-sections of borrow site, if required.
Classify suspect soils.
Lifts thickness and roller passes.
Type of soils.
Take compaction tests according to S-1015.
Verify final cross-sections.
Base estimate on yardage from cross-sections, load count or electronic grade control data.
Document on CA-EW-1, CA-EW-12 and CA-D-3. Do not duplicate the information on all forms unless necessary.