SS-840 Mechanically Stabilized Earth (MSE) Walls

Be advised SS840 dated 4/19/2013 is included in its entirety at the end of this document for reference only; the official version is available online.

Introduction

MSE walls have been constructed in the State of Ohio for over 25 years. In previous years, there were special provisions in the Contract that detailed the construction and design requirements. In the old special provisions, each wall supplier had a unique special provision. The supplemental specification (SS-840) combines all of the special provisions into one document.

SS-840 is updated frequently. Check the plans and addenda to see which version is included in the Contract. If a more recent version is available, consider adopting the new version by a change order. There may be a cost or savings involved with adopting the new version, depending on what has changed.

Below is a detail of a typical MSE wall application. This is an elevation view of a MSE wall and bridge.

Figure 840.01.A MSE Wall Elevation View

For the same bridge, a plan view is shown below.

Figure 840.01.B Plan View of the MSE Wall and Bridge

MSE wall specifications are different than the normal construction specifications. There are both design and construction criteria in the specifications. The plans will detail a three line diagram of the MSE wall structure. The internal details and the construction shop drawings are submitted after the sale of the project.

This detail shows the reinforcing mesh in general form and the undercut.

Figure 840.01.C Typical Plan Cross-Section of a MSE Wall

In the detail below, the Designer has laid out the select granular backfill and 203 embankment.

Figure 840.01.D Layout of the Select Granular Backfill and 203 Embankment

There are applications where the Designer may choose to place a wall on both sides of an embankment as detailed below.

Figure 840.01.E MSE Walls on Both Sides

General Information

The following figure details the general configuration of the MSE wall system.

Figure 840.01.F Typical Section of an MSE Wall Structure

Terms

The following are standard terms that will be used throughout this text.

Coping: The coping is used to tie in the top of the wall panels and to provide a pleasing finish to the wall top. It is cast in place.

Filter Fabric: A geotextile filter fabric is used to cover the joint between panels. It is placed on the backside of the panel joints. This keeps the soil from piping through the joints and allows excess water to flow out.

Concrete Leveling Pad: The leveling pad is unreinforced cast-in-place concrete. The concrete is 24 inches wide, 6 inches thick, and has a minimum compressive strength of 2,500 psi. Cure the cast-in-place concrete for a minimum of 12 hours prior to placing the first row of facing panels.

Original Ground: The existing ground surface at the site.

Random Backfill: Random backfill is the backfill that is allowed in normal embankment construction.

Select Granular Backfill: Select granular backfill is the granular backfill that meets the gradation, corrosion, unit weight, internal friction angle, and any other requirements.

Soil Reinforcement: Soil reinforcement holds the wall facing panels in position and provides reinforcement for the soil. The soil reinforcement can be strips, grids, or mesh. The reinforcement can be made of steel (inextensible materials) or polymers (extensible materials).

Spacers: Wall panel spacers are typically ribbed elastomeric or polymeric pads. They are inserted between panels to help provide the proper spacing. Proper spacing keeps the panels from having point contact and spalling the concrete.

Wall Facing Panel: Wall Facing panels or panels are used to hold the soil in position at the face of the wall. The panels are made of precast concrete.

Wall/Reinforcement Connection: This is where the connection is made between the wall facing panel and the soil reinforcing.

Wood Clamps: Wood clamps are pieces of wood with a steel bolt. It is used to hold the panel in place once the panel is set. The panel is not released from the crane until the wood clams are in place and tight.

Wooden Spacers: Wooden spacers are used to space the panels at the 3/4 inch-vertical spacing. The spacer is held between the panels to ensure the joints are not too close or far away.

The wooden wedges should be made from any hard wood.

Wooden Wedges: Wooden wedges are used to help hold the panels at the correct batter during the filling operation. The wooden wedges should be made from hard wood, such as oak, maple, or ash.

Figure 840.01.G MSE Wall Parts

Construction (840.06)

The wall system consists of the original ground, concrete leveling pad, wall facing panels, coping, soil reinforcement, select backfill, and any loads and surcharges. All of these items have an effect on the performance of the MSE wall and are taken into account in the stability analysis. A change in any of these items could have a detrimental effect on the wall. The construction sequence follows:

Wall Excavation (840.06.C)

There are many instances that the MSE wall is constructed in a cut section. This means that the excavation behind the wall needs to be supported temporarily in order to construct the wall. A pay item for cofferdams and excavation bracing will be included in all MSE wall plans, but if it is missing, the specification states that the cost for cofferdams and excavation bracing are included with the MSE wall pay item. The Contractor is responsible for supporting the wall excavation. All work to support the excavation or to fill the void behind the wall will be the responsibility of the Contractor.

Figure 840.06.C.1 Excavation and Select Granular Backfill Areas

Figure 840.06.C.1 shows the wall excavation and embankment areas. All of the area below the dotted line is paid for under wall excavation. All the area in the reinforced zone is filled with select granular backfill. The area below the leveling pad is filled with undercut material. Below is a field view of the same situation.

Figure 840.06.C.2 Area Behind the Wall

Foundation Preparation (840.06.D)

Preparation and Compaction

The MSE wall footprint area needs to be prepared in the leveling pad, soil reinforcement, and select granular backfill areas.

Figure 840.06.D.1 Foundation Preparation

Figure 840.06.D.1 above shows a track hoe excavating down to the MSE wall foundation. All organic matter, vegetation, slide debris, and other unstable materials, detailed as unsuitable in 703.16, needs to be removed. Once the unsuitable soil is removed, 1 foot outside of the foot print formed by the leveling pad and soil reinforcement needs to be compacted. The foundation needs to be compacted to meet the requirements of 203.07. If the foundation material is granular then the material needs to be compacted by one of the test section methods detailed in S-1015.

Once the foundation is compacted, then the foundation for the wall needs to be graded level for the full-length and width of the leveling pad and the soil reinforcement.

Foundation Evaluation

Once the foundation is compacted, the Department needs to evaluate the foundation. Contact the District Geotechnical Engineer or the plan design soils consultant to evaluate the foundation. This can be paid for through continuing services during construction through the project design coordinator. The DGE or soils consultant will evaluate the soil conditions. In the design phase, a bearing capacity and stability analysis was performed for the MSE wall based on the plan borings. This needs to be reevaluated based on the existing soil conditions during construction. The DGE or soils consultant will make a field visit to the site to determine if the foundation soils found during construction meet the soil conditions designed for in the plans. They will then report to the Department to give their results. The Contractor’s pay depends on receiving this report so the Contractor will prompt the Department to make this evaluation.

The project should review the soils’ consultant report. The project should ensure that the excavated soils match the soil borings performed to design the wall. If the existing conditions do not match plan soil borings or there are any unusual problems with the report, contact the State Construction Geotechnical Engineer.

Undercut and Drainage

Drainage and the foundation conditions are important parameters of the MSE wall system. Therefore, many contracts will detail an undercut. If an undercut is in the plans, the foundation work detailed above should be performed on the foundation of the undercut.

The following sketch details a standard undercut.

Figure 840.06.D.2 Standard Foundation Undercut

Once the foundation of the undercut is compacted, the drainage pipe is constructed. The plans will detail the pipe with a pay item. The pipe must be outletted. There will be at least 50 feet of outlet pipe in the plans to outlet the pipe. The project will have to look for an outlet if it is not detailed in the plans. Pipe, manholes, and other items can be used as a drainage outlet.

If the pipe cannot be drained, move the pipe to the outside of the wall until it can be drained. The dotted pipe above the leveling pad, in Figure 840.06.D.2, represents this pipe. It is shown on the inside of the wall, but there is no need to put the drain on the inside of the wall. It can also go on the outside of the wall. The sand on the inside is free draining.

Figure 840.06.D.3 below shows a 5 foot undercut operation. The replacement material in this case was a well graded blast rock. The material of choice for foundation replacement should be Item 203, Granular Material Type C. The upper portion should be chocked off with at least 1 foot of Item 203, Granular Material Type B. Geotextile Fabric Type D should be placed below the Granular Material Type C. This will prevent the piping of fines from the top and the bottom of the Granular Material Type C.

Figure 840.06.D.3 Replacing the Foundation

Leveling Pad Construction (840.06.E)

Once the foundation is compacted and prepared, a 2-foot wide and 6-inch thick un-reinforced concrete pad is constructed. The purpose of this pad is to serve as a guide for the wall panel erection. This leveling pad is not intended to provide significant structural foundation support in the final configuration of the wall, but there is significant construction panel loading on the leveling pad. Therefore, it must be properly constructed and on a firm foundation in order to minimize potential wall movements during the construction of the wall.

Figure 840.06.E.1 Leveling Pad Construction

The leveling pad is important to the construction of the wall, because the leveling pad sets the horizontal and vertical alignment of the wall. It must be in the correct horizontal position, level, and at the correct grade.

Figure 840.06.E.2 Accurate Leveling Pad Construction is Important

If the final wall is not level, the panels will bind against each other causing spalling of the edges and corners. If the wall is not started correctly, the finished product is seldom satisfactory.

No more than 2 shims (each 3/16 inch thick) should be required to level the panels on the leveling pad. If level cannot be obtained with two shims, then the leveling pad and the bottom of the panels needs to be checked.

Figure 840.06.E.3 Improper Shimming

Under no circumstances are bearing pads allowed on the leveling pad. Bearing pads can create point loads on the panels and allow for movement of the panels during construction.

Figure 840.06.E.4 Bearing Pads are Not Allowed on the Leveling Pad

Care must be taken to ensure the leaving pad is correctly aligned. The leveling pad is 24 inches wide to allow for some alignment errors and inconsistencies, for example, when going around corners and curves. In addition, the wider leveling pad will supply more support during construction.

Do not allow any overhanging of the panels off the leveling pad. If this happens, stop the construction and investigate the problem. If needed, reconstruct the leveling pad.

Figure 840.06.E.5 Improper Overhang

Leveling pads that change in elevation have special challenges in design and construction. Figure 840.06.E.6 below details this challenge. This figure is a general step-up figure with some of the dimensions changing in the new SS-840.

Figure 840.06.E.6 Change in Leveling Pad Elevation

The challenge is to arrange the leveling pad and panels so that when this elevation change occurs, the panel is almost fully supported by the leveling pads. Multiple elevation changes are even more difficult to construct. In all cases, a 6-inch maximum overhang along the wall is allowed. The minimum overhang distance along the wall is approximately 3 inches.

Figure 840.06.E.7 Acceptable if Less than 6 inch Overhang

The concrete leveling pad must cure for at least 12 hours before wall panels can be placed.

Figure 840.06.E.8 Finished Concrete Leveling Pad

Wall Panels Types and Parts (840.04.A)

Wall panels come in many shapes and sizes. The most common are the square and rectangular. They can be custom built into any configuration that will fit together. The front face can have any type of finish, shape, texture, or other surface treatments that can be formed.

Figure 840.04.A Reinforced Earth Panels

Figure 840.04.B Rectangular Panels

Figure 840.04.C Textured Finish Panels

Corner Panels

Corner panels provide a good connection between the two walls and act like slip joints for the wall allowing differential movement between the two walls.

Figure 840.04.D Corner Panels

Slip Joints

Typically a slip joint is used to handle large differential vertical movement of the wall. There are two in the figure below, one on each side of the corner section.

Figure 840.04.E Corner (front) and Slip Joints (One on Each Side)

Handling, Storing and Shipping Panels (840.05.H)

Panels should be stored flat and on spacers or dunnage. Spacers are typically sent by supplier on pallets of panels. Spacers protect the galvanized soil reinforcement connections from being bent or damaged by other panels. Panel faces should be kept away from areas that are muddy to prevent staining of the face of the panel. The project should ensure that panels don’t have spalling or cracking upon delivery to the site.

Correct storage is shown in Figure 840.05.A. Note that the dunnage height is more than the soil reinforcement connections to minimize damage.

Figure 840.05.A Proper Panel Storage with Dunnage

Figure 840.05.B is an example of improperly stored panels. The panels in this case can get chipped or cracked.

Figure 840.05.B Improper Panel Storage

The soil reinforcement connections also can get bent.

Figure 840.05.C Damaged Tabs

Panel Inspection

Panel Dimensions and Tolerances (840.05.G)

When the panels first arrive at the project, the panel documentation needs to be checked. The panels come with a TE-24. The documentation required with this TE-24 is a record of final inspection of all precast components and the measurements of the tolerances, strength, and dimensions of all panels. As one final check, the dimensions need to be randomly checked at the project. The shipment paperwork, shop drawings, and the actual panel dimensions need to be compared to ensure that issues are found in a timely manner. The earlier in the process that these problems are found, the easier it will be to correct the issues. Some of the panel items to pay particular attention to are:

1. Length, width, and thickness.

2. Squareness.

3. Finish.

Physical measurements of the panels are required. The project should use a tape and carpenters square to check the above. All of these dimensions have an effect on the Contractor’s ability to construct the wall within the specification tolerances.

Figure 840.05.D Checking the Squareness of the Panel

Precast Panel Rejection (840.05.J)

Damage to the Galvanized Soil Reinforcement Connections

If the soil reinforcement connections are damaged to the point that it inhibits the soil reinforcement from being attached, then the panel needs to be rejected. Many times the connection is filled with residual cement or concrete that does not allow the soil reinforcement to be connected. If this is the case, have the Contractor clean out the connections. Do not cut the soil reinforcements.

If the connections are bent more than 15 degrees from perpendicular, the panel needs to be rejected. When bent beyond 15 degrees, the galvanizing is compromised and cannot be repaired.

Damage to the Panels

The panels also need to be inspected for damage. Panels can be damaged almost anywhere during the manufacturing or construction process. Many of the chips and cracks are caused by poor handling. Chips or spalls can be prevented by using nylon straps in the handling process. Cracks can be avoided by taking care in the handling process. There is a list of defects and damages in 840.05.H that are sufficient reason for rejecting a panel. Depending on the severity of the damage, the Contractor may propose a repair.

Figure 840.05.E Rejected Cracked Panel

Figure 840.05.F Rejected Lifting Spall

Figure 840.05.G Repairable Lifting Strap Spalling

Figure 840.05.H Repairable Handling Spalls

Wall Erection (840.06.G)

Panel Identification

At this point, we have constructed the foundation, added drainage, checked the materials, and constructed the leveling pad.

There is one last step we need to perform before we construct the wall; the wall and shop drawings must be checked to ensure that the correct panels are being used in the correct location along the wall. Depending on the wall height, the panel shape, or design, the number of soil reinforcement connections on the back of the panel may vary. The panels with the most connections will typically be in the lower panels of the wall. In the upper portions of the wall, the number of connections may be less. It is important that the panels are used in their proper position. Below is a typical shop drawing showing the panel organization.

Figure 840.06.G.1 Typical Panel Erection Shop Drawing

The erection drawings have a numerical code on each panel that depicts its position in the wall. In the above shop drawing, the letter A denotes full-height panels in the first row and the subsequent rows until the shape changes as the panel is just below the coping. The letter B denotes half-height panels in the first row. The codes HX, F11, L11, KX, K, E, EX, HJJ, KJJ, LJJ, DJJ, and EJJ denote panels just below the coping. Note the combination of letters. R or L will be used to denote the right or left side of the wall. A number that follows the letters denotes the number of tie strips required for the panels. Below is a code that details the panel letter and numerical system.

Figure 840.06.G.2 Code for Panel Placement (Reinforced Earth)

The code that is detailed above is for Reinforced Earth walls. The code for other wall systems will be different, and the code for a particular wall system may change at any time. The codes are marked on the back of the panels for easy reference during construction. Below is a photo of the marking on the back of a panel.

Figure 840.06.G.3 Actual Panel Markings

The above markings show piece A has 3 tie strips and is on the right side of the wall. Other required markings include date of manufacturing, production lot number, and the precaster’s and accredited manufacturer’s inspection and acceptance marks.

Placing the Panels

Picking up the panels is an important aspect of the construction procedure. If the panels are not properly picked up, spalling or cracking can occur. The figure below shows the correct method of picking up the panels. The crane lifts the panel so that no concrete to concrete contact occurs.

Figure 840.06.G.4 Picking up the Panels

The correct placement of the first row or two of panels is very important. When the panel construction is not started correctly, the finished product is rarely satisfactory.

In the figure below, a chalk line is placed on the leveling pad to properly align the panels along the leveling pad. Sometimes a 2×4 is used to align the panels. Adjust the alignment using a crowbar as shown below. At this point, the panel is still supported by the crane.

Figure 840.06.G.5 Proper Placement

As one last check of the horizontal alignment, the panel to panel horizontal offset needs to be checked. Use a straightedge across the panel horizontal joints to ensure that the panel to panel horizontal offset does not exceed 1/2 inch.

The first row may be composed of both half- and full-height panels. A photo of full- and half-height panels is shown below. The panels need to be in proper alignment and level.

Figure 840.06.G.6 Half Height Panels

Horizontal Leveling

Once the panel is placed on the leveling pad, the panel needs to be leveled horizontally. A 6-foot level rod is placed on the top surface of the panel to determine if it is level.

Figure 840.06.G.7 Proper Horizontal Leveling

If it is not, shims are placed under the panel in order to make the panel level. Galvanized metal washers or rubber shims are allowed. A maximum 3/8 inch in total shim height, at any location, is allowed. If more shims are required, then the leveling pad is not level or the panel bottoms are not flat. In either case, the issue is the Contractor’s responsibility to resolve.

Figure 840.06.G.8 Metal Shims to Level the Panels

Horizontal Joint Spacing

Without the correct joint spacing, panel corners will crack and spall with the wall settlement. Spacing blocks must be used. As the panels are placed together, the 3/4-inch spacers are placed in the joints. The panels are maneuvered so that there is contact between both panels and the joint spacer. The required joint spacing is 3/4 inch ± 1/4 inch. If this spacing cannot be achieved, the Contractor is required to submit an action plan to correct the problem. The spacer is shown in the figure below. If the panel is moved during the joint spacing adjustment, then the horizontal leveling should be checked again.

Leave the horizontal spacers in until half of the panel height is filled with backfill.

Figure 840.06.G.9 Wooden Joint Spacers

Vertical Alignment

The panels need to be set with a backward batter toward the inside of the wall. The typical batter is about 1/8 inch per foot of panel height or about 1/2 to 1 inch per panel. Compacting the backfill behind the wall pushes the panel outward, so the panel will be vertical once the fill is placed against it. The amount of batter is adjusted for the site conditions, such as backfill properties; the finer sand may require a more batter. If a fine graded material, such as foundry sand is used, then it may require a 1-inch batter. A well-graded, crushed limestone may require a 1/2-inch batter.

Figure 840.06.G.10 Batter Check

A level with a batter spacer is placed on the outside or inside of the wall. Use the outside of the wall unless textured. The batter spacer can be used on the top or bottom of the level. If the level is used on the outside of the wall, the batter spacer is used on the top of the level. If the level is used on the inside of the wall, the spacer is used on the bottom of the level. The spacer is usually duct taped on to the level at a thickness of the batter. In the figure below, it shows the batter spacer being used on the inside of the wall.

Figure 840.06.G.11 Vertical Leveling Spacer on the Inside of the Wall

The level can also be used on the outside of the wall as shown below.

Figure 840.06.G.12 Vertical Batter on the Outside of the Wall

Vertical and horizontal alignments and joint spacing needs to be checked one last time prior to temporarily locking the panel in place. For the entire time the horizontal leveling, joint spacing and vertical alignment is being adjusted, the panel is still suspended from the crane so that the panel is not damaged.

Triangular Wedges and Wood Blocks

Wooden triangular wedges are used to lock the panel into vertical alignment once the wall is battered with the level. The wedges are shown below on the leveling pad.

Figure 840.06.G.13 Wooden Wedges for Vertical Alignment

No more than three levels or rows of the wooden wedges should be placed in the wall without removing the lower row. If more than three levels of wedges are used they may become bound in the wall making them very difficult to remove and can cause the panel to spall.

Wooden clamps are used to hold the panels together. Wooden clamps are two pieces of wood held together with a long bolt. The bolt is tightened to hold the panels together.

Figure 840.06.G.14 Wooden Clamps

Triangular wedges are also used in combination with the clamps to secure the panels as shown in the figure below.

Figure 840.06.G.15 Triangular Wedges and Wooden Clamps

External bracing is required for the first row of panels to maintain stability and alignment. Typical bracing is shown below.

Figure 840.06.G.16 Proper Bracing

At this point, the geotextile fabric and the select granular backfill are placed to the height of the wooden clamps. These steps will be described in detail later.

When panels are placed on one another, a horizontal bearing pad is used to separate the panels. A minimum of two bearing pads are used. The horizontal joint should be 3/4 inch at this point. Some Accredited Wall Systems may supply thicker bearing pads. This is anticipation of the bearing pads deflecting under the load of the wall. Check the accepted wall shop drawings to ensure that the thicker pads are allowed.

Figure 840.06.G.17 Bearing Pads on the Second Row

Subsequent panel rows are placed between panels that were previously placed. The ability to properly space and align these rows relies on the proper placement of the lower rows. All of the error produced by the lower rows is propagated upward and is difficult to correct. The same leveling, joint spacing, vertical, and horizontal alignment applies to all the rows.

Figure 840.06.G.18 Panel Placement

Panel-to-panel vertical offset needs to be checked as soon as the next row of panels is placed. Use a straightedge across the vertical joints to ensure that the offset between panels is less than 1/2 inch.

Figure 840.06.G.19 Second Row of Panels Placed

The process starts all over again as crow bars are used to align the next row of panels.

Figure 840.06.G.20 An Existing Joint Offset Problem

Alignments need to be checked periodically to ensure proper alignment. This will ensure that problems are spotted early and corrections can be made before the panels get too far out of alignment.

Figure 840.06.G.21 Wall Alignment

As stated before, the panels are battered back so that the fill placement can move them forward into a vertical position. After the fill is placed, check the vertical position of the wall. After the third row of panels is placed, use a plumb bob to check the vertical alignment. Hold the plumb bob at the top of the panel and measure the out of plumbness, as shown below.

Figure 840.06.G.22 Checking Vertical Alignment with a Plumb Bob

The tolerance is 1/2 inch in 10 feet. By using a 10-foot straightedge and a level or a plumb bob, this tolerance can be measured. At no point along the straightedge can any portion of the panel be more than 1 inch away from the string or straightedge.

Figure 840.06.G.23 Measure from the Wall to the String (Out of Plumb Here)

A summary of the wall erection tolerances are listed below:

1. Vertical Tolerance: 1/2 inch overall and 1 inch at any point.

Use a 10-foot straightedge,

2. Horizontal Tolerance: 1/2 inch overall and 1/2 inch at any point.

Use a 10-foot straightedge.

3. Panel to Panel Tolerance: 1/2 inch horizontal and vertical.

Use a 6-foot straightedge.

Figure 840.06.G.24 Panel Tolerances

Filter Fabric Placement and Inspection

Filter fabric is placed across the joints so that the granular backfill does not leak through the joints to the outside of the wall. The minimum lap on each side of the joint is 1 foot on each side of the joint and 1 foot along any cut piece of fabric along the joint. These requirements apply to horizontal and vertical joints.

The fabric is cut in lengths to cover the horizontal and vertical joints. Once the fabric is cut, the fabric is laid on a flat surface. An adhesive is used to hold the filter fabric in place until the select granular backfill is placed over the joints. A thick bead of the adhesive, approximately 1/2 inch in diameter, is applied around the entire perimeter of the fabric, about 2 inches from the edges of the fabric. See the figure below.

Figure 840.06.G.25 Correct Application of the Adhesive

Figure 840.06.G.26 Fabric Completely Covering the Joints

Once adhesive is applied to the fabric, it is immediately placed on the wall. Ensure that the fabric is placed on the wall before the adhesive dries. The fabric needs to fully engage the wall at all locations to ensure that the sand does not leak through the joints.

Figure 840.06.G.27 Wrong Application of the Adhesive on the Wall

As shown above, randomly placing adhesive on the wall does not ensure that the joint is properly sealed. More adhesive is not necessarily good. Correctly applied adhesive and the appropriate placement of the fabric is the solution.

In the past, some projects have only glued the top portion of the fabric applied to a horizontal joint. This method should be discontinued and not be allowed.

Figure 840.06.G.28 Partial Gluing (Do not Allow this)

Small tears or wrinkles in the fabric can cause leaking of the sand. Any leaking of the sand through the joints is not tolerable. Leaking sand is like a leaky water pipe; it never gets better with time, it only gets worse.

Once the fabric and the backfill are placed, the project should go around to the front of the wall to inspect the joint spacing and the fabric’s ability to hold the sand behind the wall. Take a flashlight and inspect the joints. Look to see if the fabric is in place and holding the sand back.

Look for deposits of sand in the horizontal and vertical joints, as shown below.

Figure 840.06.G.29 Sand in the Joints on the Outside of the Panels

Sand deposits may be caused by sand falling over the wall during construction or the sand is leaking through the joints. By carefully inspecting the joints, the source of the sand deposit will be found. In the figure below, the sand is leaking out of the joints and being deposited on the ground.

Figure 840.06.G.30 Sand Falling from Several Joints

After further inspection of the wall from behind, it was found that the fabric was not placed in the upper portion of the MSE wall. This project was about three-years-old at the time of the inspection. A thorough inspection during the construction of the wall would have prevented this maintenance problem.

Figure 840.06.G.31 No Fabric Placed Behind the Wall

Below is a photo of a wall, which was taken shortly after construction. As you can see, there are sand deposits at the bottom of the slip joints. In this case, the fabric was either not placed or improperly placed.

Figure 840.06.G.32 Sand Piles around Slip Joints

In the figure below, looking behind the wall at a typical slip joint during construction, you can see that the fabric has to go around a bend. Careful construction in this location is required. When placing fabric around corners or obstructions, leave the fabric loose so that it does not tear during the placement of the backfill in the corner.

Figure 840.06.G.33 Fabric Placement around a Slip Joint

There are a lot of other items of work that obstruct the proper placement of the fabric in this situation. In the figure below, there are the reinforcing steel, wooden clamps, and a settlement plate that the fabric needs to go around. There is ample opportunity for sand to leak around the fabric if we are not careful.

Figure 840.06.G.34 Obstructions near a Slip Joint

The joint spacing needs to be reexamined in the front of the wall. We have previously checked and recorded the joint spacing when the panels were constructed. There may be cases where after the wall is constructed, the joint spacing is wider than the allowable 3/4 inch plus 1/4 of an inch.

Figure 840.06.G.35 Wide Joint and Exposed Fabric

The joint gap in the above figure is almost 1-3/4 inch. The gap is wider than the panel’s ship lap, therefore, exposing the fabric. The width of the ship lap is about 1-1/2 inches. In the above case, the Contractor needs to be instructed to place expansive foam and caulk to the joint to prevent the fabric being exposed to sunlight.

Sunlight can cause the fabric to deteriorate with time, whether direct or indirect. A flashlight is used to minimize sunlight exposure to the fabric. A flashlight is held perpendicular to the joints, about 6 inches away from the joint. The described flashlight test is shown in the figure below.

Figure 840.06.G.36 Flashlight Test

If the light from the flashlight can be seen on the fabric, then the joint needs to be sealed. Expanding foam and caulk is used to cover the fabric.

There have been instances where, after the wall has been constructed, the fabric is destroyed during water jetting operations. Water jetting is used to clean the panels prior to sealing; therefore, examine the joints after the sealing operation.

As a final note on the wall construction, continue to monitor the wall throughout the duration of the project. The wall is designed and constructed to tolerate movement. Too much movement is detrimental to the wall and the structural items around the wall.

Select Granular Backfill Placement (840.06.I)

Material

The granular backfill materials have special requirements that are not normally associated with granular material in other items of work. There are material requirements such as pH, resistivity, chloride, and sulfate levels. These requirements minimize the corrosion of the metal soil reinforcement. The project and district test lab need to review and evaluate the test data for these requirements. Ensure that the test results meet the specification requirements and that the correct tests were taken on the materials. If the backfill material does not meet these requirements, then there is a high probability that the metal soil reinforcement will prematurely corrode and the life of the MSE wall will be shortened.

Another requirement is the internal angle of friction. The internal angle of friction is critical to the design of the wall. The wall design and the factor of safety are sensitive to numerical value of the friction angle. The factor of safety can change dramatically with only a few degrees of friction angle change. The design friction angle is 34 degrees. The test ensures that the design assumption is valid.

The specification allows the use of granular material Type 2 which is old Item 310 material. It can be very fine sand or a coarse 304 type material. Since economics drives the material choice, the vast majority of the time sand is used.

The specification also allows the use of Item 304 material. This material is a well graded and very stable material.

It is a requirement to use the Item 304 material for the first 3 feet of backfill behind the wall. This is a stronger material and is more resistant to the influences of water. After the first 3 feet are placed, the sand or the 304 may be used.

Select Granular Backfill Placement and Compaction

The below placement and compaction procedures were developed to produce uniform compaction of the select granular backfill (SGB). Uniform placement and compaction of this material is essential in order to keep uniform pressure against the wall as it is constructed. Unnecessary compaction or non-uniform compaction of this material can create bulges in the wall or loose areas in the backfill behind the wall. This procedure is to be followed all the way to the top of the wall.

On the initial row of panels (and only the initial row of panels) the backfill is not placed against the panel until the first layer of soil reinforcement has been connected and the initial layer of backfill is placed and compacted on top of the soil reinforcement. This is to keep the bottom of the panels from “kicking out.” If the SGB cannot be compacted effectively below the first row of soil reinforcement, because some manufacturers may have mesh that we cannot compact through, then the wall supplier will need to design a kicker to prevent the wall from kicking out at the bottom.

Figure 840.06.I.1 Backfilling for the First Panel Only

Once the backfill is placed and compacted to the elevation of the first layer of soil reinforcement as shown in Figure 840.06.I.1, the soil reinforcement is connected. Then the next loose lift is placed on top of the soil reinforcement 3 feet away from the wall. The material is then leveled by moving it parallel to the wall and windrowing the material toward the soil reinforcement ends and away from the wall. See Figure 840.06.I.2 for the spreading operation details. This SGB material which is 3 feet away from the wall is then compacted in the same way as it was placed.

Figure 840.06.I.2 Procedure for SGB Placement and Compaction

Once this is completed, the void is filled and compacted next to the wall to the elevation of the soil reinforcement. The material void left above the soil reinforcement is then placed and compacted. Place and compact this inner most 3 feet as detailed in Figure 840.06.I.3. Within 3 feet of the wall, the SGB is compacted with six passes of a mechanical tamper or vibratory plate compactor. The compaction equipment should have a centrifugal force between 1/2 to 2 tons.

Figure 840.06.I.3 Place and Compact the SGB Next to the Facing Panels

Use the procedure detailed in Figures 840.06.I.2 and 840.06.I.3 for the SGB placement and compaction procedure for the remaining sections of wall.

The SGB is placed in maximum 8-inch loose lifts. It may be helpful to mark the lift thicknesses on the back side of the wall panels. The action of moving the SGB parallel to the wall and windrowing or compacting the material toward the reinforcement ends and away from the wall takes out the slack in the reinforcement and locks the reinforcement and the panels in position.

Figure 840.06.I.4 Improper Spreading Technique

(From back to front is improper)

Any slack in the reinforcement should be removed to avoid excessive panel movement. With geogrid soil reinforcement, some tension needs to be applied to the reinforcement by means of a kicker tension device or a rod during this backfill placement.

Figure 840.06.I.5 Final Compaction Operation Next to the Wall

Consistent placement and compaction of SGB are one of the keys to a good performing MSE wall.

Inspection and Compaction Testing (840.06.N)

No compaction testing is performed on the SGB within 3 feet of the wall. For the SGB, more than 3 feet from the wall facing panels, smooth-drum vibratory rollers weighting between 6 and 10 tons are required to compact the material. The compaction testing is performed according to Supplement 1015 and SS 878.

SS 878 details the general inspection and compaction testing requirements when these services are hired through the Contractor. All of the inspection and compaction procedures that are required for ODOT inspection personnel are required for the Contractor’s personnel under SS 878. A trained compaction and inspection person is required under this specification. All of the Department inspection and compaction forms are to be used.

Supplement 1015 details the inspection and compaction procedures to be employed during the work.

At the beginning of the work, a test section is constructed to determine the density requirements for the select granular backfill. The moisture requirements are determined by using the moisture density curve for the Method A test section. For the Method B test section, the moisture requirements are determined by constructing several test sections at different moisture contents. For determining which test section is used, see Supplement 1015.

The select granular material is compacted between 3 percent below and optimum moisture content. If additional water is required after spreading the material, then water must be added to meet these requirements. The moisture content of the select granular backfill material prior to and during compaction is to be uniformly distributed throughout each layer of material. If watering is required after spreading, the project should dig up the material to ensure that this requirement is met.

Figure 840.06.N.1 Taking a Compaction Tests

Once the moisture content is correct, the test section is constructed to determine the density requirements for the remaining areas of the select granular backfill. This test section is approximately 40 square yards. This test section is compacted until a maximum density is achieved. The number of passes and the maximum density is used in the remainder of the work. A minimum of 98 percent of the maximum density is required. A new test section should be constructed if the compaction tests are not close to the maximum value. Use the same number of passes if the material or foundation conditions change.

In the figure below, the compaction starts 3 feet away from the wall and proceeds to the back of the soil reinforcement. In the background, the area within 3 feet from the wall is compacted after the roller compaction is complete. This procedure is detailed in the previous section.

Figure 840.06.N.2 Smooth-drum Vibratory Compaction Equipment

Wall Drainage (840.06.F)

At the end of each day’s operation, the Contractor is to shape the last layer of backfill to allow rainwater to runoff away from the wall face. The drainage system is under or in front of the wall. This will permit the water to dissipate from the system. The SGB of the wall can be drained laterally to dissipate out to the sides. Drainage problems can develop similar to the figure below.

Figure 840.06.F.1 Washout around the Soil Reinforcement

Water ponding in front of the wall has been a problem is the past. In the figure below, you can see the ponding of the water in front of the wall. This is not acceptable.

Figure 840.06.F.2 Water Ponding in Front of the Wall

It is required to pump the water out of this area immediately after the water is ponded. In addition, once the wall is erected up to the ground elevation, this void is filled with embankment material. This will further stabilize the wall.

If water is ponding behind the wall during construction as shown below:

Figure 840.06.F.3 Water Ponding Behind the Wall

Then collect the water by using a drainage curtain as detailed below:

Figure 840.06.F.4 Drainage Blanket

Side slope erosion has been a problem in the past. One solution has been to construct 2 feet of embankment on the side slopes. This will bury the highly erosive select granular material and erosion can be minimized.

Figure 840.06.F.5 Protection of the Erosive Side Slopes with Embankment

Soil Reinforcement Installation (840.06.H)

Soil Reinforcement Storage

The soil reinforcement is used to tie the wall to the soil. Like the panels, the soil reinforcement should be stored on dunnage and carefully handled to prevent damage. Damage may include bending of the metallic reinforcement and damaging the galvanization. The geogrid soil reinforcement should not be torn, cut, left in the sun, or otherwise damaged.

No equipment should be allowed to run directly on the reinforcement.

Figure 840.06.H.1 Reinforcement Storage on Dunnage

The project should check for required length and gauge of steel reinforcement. Check the condition of steel reinforcement upon delivery to the site. Below is a typical plan view of the soil reinforcement on a project. The length of the reinforcement from the wall is directly proportionate to the height of the wall. The wall height below is the highest in the center and the length of the reinforcing is the longest. The length of the reinforcing cannot change from the bottom to the top of the wall. It can only change along the wall due to changes in the height or design changes.

Figure 840.06.H.2 Typical Reinforcement Layout

Below is a detail of a cross-sectional view of the soil reinforcement in the same wall. Notice the soil reinforcement connection to the wall and regular intervals. The length of the reinforcement is the same from the bottom of the wall to the top of the wall. Many of these walls are placed below an abutment as detailed below.

Figure 840.06.H.3 Cross-Section of the Soil Reinforcement Layout

Below are the reinforcing mesh codes for a Foster wall. These codes were used on past projects. For Foster walls, the reinforcing mesh will change frequently. The project should familiarize themselves with the codes on the shop drawings and ensure that the correct mesh types are placed in the proper location.

The figure below details the wire mesh codes. Careful review of these keys is required by the project.

Figure 840.06.H.4 Reinforcing Mesh Details

Below is a sample of how the reinforcing mesh is laid out as it relates to the panels. The panels are numbered in the example and the type of reinforcing mesh is detailed beside the panel type.

Figure 840.06.H.5 Reinforcing Panel and Reinforcing Key

Typically, the reinforcement is placed perpendicular to the wall face. Any slack in the reinforcement should be removed. The geogrid soil reinforcement should have some tension placed in the reinforcement. By using the placement and compaction procedure detailed in the previous section, it will keep the tension in the soil reinforcement.

Once the fill is compacted to the elevation of the soil reinforcement, the soil reinforcement can be attached to the facing panels and placed perpendicular to the face of the wall on top of the compacted material.

Connections

Connecting the soil reinforcing to the wall is relatively simple operation. There are three connections that will be detailed below.

Reinforced Earth Connection

A Reinforced Earth wall’s connections and soil reinforcement consist of galvanized strips, tabs manufactured in the wall, and nuts and bolts to connect them. There are tabs with holes that stick out of the wall about 3 inches. The tabs have a top and bottom and go around the strips when they are connected.

Figure 840.06.H.6 Reinforced Earth Connections and Strips

At times, there is concrete inside the tabs that make it difficult to place the strips inside the tabs. The concrete needs to be cleaned out to line up the holes. Many times the Contractor will cut the strips instead of cleaning out the concrete. Do not allow the strips to be cut in the field. This can reduce the strength of the connection. Also, the galvanizing of the strip will be compromised and the strip will prematurely rust.

Figure 840.06.H.7 Tabs for Reinforced Earth Connections

Once the holes are lined up, the bolt is inserted from the bottom up and the nut is tightened. By placing the bolt from the bottom, it is easy to see if the nut has been placed on the connection.

Figure 840.06.H.8 Bolted Reinforced Earth Connection

Below are multiple strips connected to the wall for a Reinforced Earth wall. Leaving the select granular backfill lower at the tabs is acceptable. The select granular backfill needs to be as close to the strips as possible for all wall types.

Figure 840.06.H.9 Reinforced Earth Multiple Connections to the Wall

Wire Mesh Connection

The connection for steel wire mesh soil reinforcement consists of hooked eyelets in the panels and reinforcing mesh with two transverse bars at the end. The end of the wire mesh is laid with the two transverse bars resting on top of the hooked eyelets. A rod is inserted through the eyelets, locking the mesh into place, as shown below. Wooden wedges are then hammered between the wall and the mesh to put the eyelets in full contact with the mesh and the soil reinforcement in tension.

Figure 840.06.H.10 Wire Mesh Type Connection

Below is a typical layout of the soil reinforcement of a wire mesh wall.

Figure 840.06.H.11 Mesh Steel Laid Out

Geogrid Soil Reinforcement Connection

The connection for geogrid soil reinforcement consists of short sections of geogrid cast into the panels and a plastic bodkin bar. The ribs of the geogrid soil reinforcement are meshed with the short sections of geogrid that are cast into the panels. The plastic bodkin is then weaved between the two sets of ribs and the soil reinforcement is pulled tight. The completed connection is shown below.

Figure 840.06.H.12 Geogrid Soil Reinforcement Connection

Figure 840.06.H.13 Overview of Geogrid Soil Reinforcement

Obstructions

There are times when the soil reinforcements have to go around obstructions. It is not acceptable to simply leave out the reinforcement at that location. This would create a weak location along the wall.

At horizontal obstructions, such as pipes, the reinforcement should not be angled more than 15 degrees up or down. All situations that exceed 15 degrees must be detailed on the accepted shop drawings or acceptable to the Office of Geotechnical Engineering. The soil reinforcement must have a 4 inch clearance above or below the obstruction. When clearing horizontal obstructions, the reinforcement should be smoothly curved around the obstruction. The reinforcement should not be kinked at any time.

The detail below shows a horizontal obstruction lower than the soil reinforcing and connection.

Figure 840.06.H.14 Soil Reinforcement going over a Horizontal Obstruction

The detail below shows a horizontal obstruction higher than the soil reinforcing and connection.

Figure 840.06.H.15 Soil Reinforcement going under a Horizontal Obstruction

The photo below shows the soil reinforcement going under a storm sewer line.

Figure 840.06.H.16 Soil Reinforcement going under a Storm Sewer Line

At vertical obstructions, such as piles or catch basins, if the reinforcement must be splayed more than 15 degrees for steel strips or 5 degrees for geosynthetic strips from perpendicular to the facing panels, the accepted shop drawings should detail a modification. All situations that exceed the 15 or 5 degree limits must be detailed on the accepted shop drawings or acceptable to the Office of Geotechnical Engineering. It may require additional reinforcement length to meet design.

Figure 840.06.H.17 Soil Reinforcement Splayed Around Piles

In the detail below, the soil reinforcement was designed around the inlet by using a galvanized angle in front of the inlet and keeping the reinforcing steel perpendicular to the wall. Again, this would have to be detailed on the acceptable shop drawings.

Figure 840.06.H.18 Typical Details for Obstructions

Below is a photo of the galvanized angle in front of the catch basin to allow the soil reinforcement to be placed around the catch basin.

Figure 840.06.H.19 Field Example of the Reinforcing Around an Obstruction

In the detail below, the reinforcing mesh is cut and splayed around the inlet. No angle is required in front of the inlet.

Figure 840.06.H.20 Cutting the Mesh to go around the Obstruction

Coping (840.06.K)

The coping is placed on the top of the wall. It is used to smooth out the appearance of the top of the wall and to connect adjacent panels at the top of the wall. The wall is completed when the coping is properly installed on top of the wall. The coping has to be cast in place on the top of the wall.

Here is the typical form and reinforcing steel for the coping.

Figure 840.06.K.1 Forming the Coping

Moment Slab

The moment slab is put on the top of the wall to prevent vehicles from going off the roadway. It must have a large support system to resist these loads. The reinforcing steel is shown below.

Figure 840.06.K.2 Moment Slab Reinforcing Steel

The finished moment slab is shown below.

Figure 840.06.K.3 Completed Moment Slab

If your project has a concrete pavement on top of the wall, there may be a problem with crack propagation of the barrier joints on to the pavement. Review these details carefully and make adjustments as required.

Figure 840.06.K.4 Align the Joints of the Barrier and the Concrete Pavement

Design Conflicts, Design and Construction Loads

Before the actual start of construction of the wall, the various parts of the plans (shop drawings, drainage, lighting, etc.) need to be compared to the contract wall plans to check for conflicts. A conflict may not have been noticed in the design stage. If the plans show heavy loads on the wall and the shop drawings do not indicate it, the Office of Geotechnical Engineering should be contacted. The Designer may have missed loadings from various types of structures. If they did not take these loads into consideration, the wall could bow or even fail. This also can happen for temporary loads that the Contractor may impose, such as pile driving.

Final Checks

There are various items that need to be evaluated at the end of the project, such as sand leaking out of the joints, open joints, exposed fabric settlement, and more.

There are multiple PowerPoint presentations on the ODOT website. The websites are as follows:

http://www.dot.state.oh.us/Divisions/ContractAdmin/Contracts/Conaway/Forms/AllItems.aspx

http://www.dot.state.oh.us/Divisions/Engineering/Structures/standard/MSE/Pages/default.aspx

Checklists

The following is a general checklist to follow when constructing a Mechanically Stabilized Earth wall (MSE wall). The answer to each of these should be yes unless the plans, specifications, or specific approval has been given otherwise.

YES NO

¨ ¨ 1. Has the Contractor submitted wall shop drawings?

¨ ¨ 2. Has the Contractor submitted select granular backfill certified test data?

¨ ¨ 3. Has the Contractor supplied a wall supplier’s construction manual?

¨ ¨ 4. Have the shop drawings been accepted?

¨ ¨ 5 Do we have the correct panels (shape, size, and soil reinforcement connection layout) per the accepted shop drawings?

¨ ¨ 6. Do we have the correct reinforcement (proper length and size)?

¨ ¨ 7. Have the panels and the reinforcement been inspected for damage as outlined in the specifications?

¨ ¨ 8. If any panels or soil reinforcement were found damaged, have they been rejected or repaired in accordance with the specifications?

¨ ¨ 9. Are the panels and the soil reinforcement properly stored to prevent damage?

¨ ¨ 10. Has the MSE wall area been excavated to the proper elevation?

¨ ¨ 11. Has the foundation been properly evaluated?

¨ ¨ 12. Has the drainage for the wall been installed?

¨ ¨ 13. Has the leveling pad area been properly excavated?

¨ ¨ 14. Has the leveling pad been set to the proper vertical and horizontal alignment?

¨ ¨ 15. Has the leveling pad cured for a minimum of 12 hours before any panels are set?

¨ ¨ 16. Is the first row of panels properly placed? Do they have proper spacing, bracing, tilt, and where required, do they have the spacers installed?

¨ ¨ 17. Has the proper filter fabric and adhesive been supplied?

¨ ¨ 18. Is the filter fabric being properly placed over the joints?

¨ ¨ 19. Is the adhesive being applied to the fabric then onto the wall?

YES NO

¨ ¨ 20. Is the filter fabric being stored properly (stored out of the sunlight and protected from UV radiation)?

¨ ¨ 21. Is the Contractor using the correct panels (correct size, shape, and with the proper number of connections) for that panel’s wall location and elevation?

¨ ¨ 22. Is the fill being placed and compacted in 8-inch loose lifts?

¨ ¨ 23. Is the equipment being kept off of the soil reinforcement until a minimum of 8 inches of fill is placed?

¨ ¨ 24. Are the lifts being placed by the proper method and sequence?

¨ ¨ 25. Is the fill being compacted by the correct equipment and in the correct pattern?

¨ ¨ 26. Is the proper compaction being met?

¨ ¨ 27. Is the soil reinforcement being properly connected (connections tight and all of the slack in the soil reinforcement removed)?

¨ ¨ 28. Is the soil reinforcement in the proper alignment?

¨ ¨ 29. Is the vertical and horizontal alignment being checked periodically and adjusted as needed?

¨ ¨ 30. Is the Contractor removing the wooden wedges as per the specifications? (The wooden wedges shall be removed as soon as the panel above the wedged panel is completely erected and backfilled.)

¨ ¨ 31. At the end of each day’s operation, is the Contractor shaping the last layer of backfill to permit runoff of rainwater away from the wall face or providing a positive means of controlling runoff away from the wall, such as temporary pipe, etc.?

¨ ¨ 32. Has the Contractor backfilled the front of the wall?

¨ ¨ 33. Is the coping being installed correctly?

MSE Wall Construction Do’s and Don’ts

1. Review approved shop drawings.

2. Review the Section 840 in the MOP for Mechanically Stabilized Earth (MSE) walls.

3. Verify leveling pad elevations.

4. Confirm fill material has been tested and approved before it is brought to the job site.

5. Inspect panels.

6. Inspect soil reinforcement for damage.

7. Reject all panels that are not in compliance with the plans and specifications.

8. Ensure panels, soil reinforcement, and filter fabrics are properly stored to prevent damage.

9. Ensure the reinforcing can go around all obstructions with less than 15 degrees of splay.

10. Install panels in accordance with the plans and specifications.

11. Place and properly compact fill in accordance with plans and specifications.

12. DO NOT use thick fill lifts. Fill lifts thicker than 8-inch loose lifts require more energy to compact and may move the panels out of alignment.

13. Use corner panels at all corners. If corner panels are not indicated on the plans, the designer should be notified.

14. Metallic soil reinforcement strips should not be splayed more than 15 degrees from normal. Geosynthetic soil reinforcement strips should not be splayed more than 5 degrees from normal. If reinforcement needs to be splayed more than the 15 or 5 degree limits, notify the designer.

15. Check the batter of the panels often. Adjust accordingly. The vertical alignment of the panels below the panels being installed may be affected by the compaction of the soil behind the panels being installed.

16. Check overall batter regularly.

17. When attaching filter fabric to the back of the panels, the adhesive shall be applied to the fabric, and then attached to the panel.

Out of Tolerances Conditions and Possible Causes Criteria

The following is taken out of FHWA’s Publication, “Mechanically Stabilized Earth Walls and Reinforced Soil Slopes Design & Construction Guidelines,” NHI Course No. 132042.

MSE structures are to be erected in strict compliance with the structural and aesthetic requirements of the plans, specifications, and contract documents. The desired results can generally be achieved through the use of quality materials, correct construction/erection procedures, and proper inspection. However, there may be occasions when dimensional tolerances and/or aesthetic limits are exceeded. Corrective measures should quickly be taken to bring the work within acceptable limits. Presented below are several out-of-tolerance conditions and their possible causes.

Table 840.A – Out-of-Tolerance Conditions and Possible Causes

Distress	Possible Causes
1. Distress in wall: Differential settlement or low spot in wall. Overall wall leaning beyond vertical alignment tolerance. Panel contact, resulting in spalling/chipping	Foundation (subgrade) material too soft or wet for proper bearing. Fill material of poor quality or not properly compacted.
2. First panel course difficult (impossible) to set and/or maintain level. Panel-to-panel contact resulting in spalling and/or chipping.	Leveling pad not within tolerance.
3. Wall out of vertical alignment tolerance (plumbness), or leaning out.	Panel not battered sufficiently. Oversized backfill placing and/or compaction equipment working within 3 foot zone of back-of-wall facing panels. Backfill material placed wet of optimum moisture content. Backfill contains excessive fine materials (beyond the specifications for percent of materials passing a No. 200 sieve). Backfill material pushed against back of facing panel before being compacted above reinforcing elements. Excessive or vibratory compaction of uniform, medium-fine sand (more than 60 percent passing a No. 40 sieve). Backfill material dumped to close to free end of reinforcing elements, then spread toward back-of-wall, causing displacement of reinforcements and pushing panel out. Shoulder wedges not seated properly. Shoulder clamps not tight. Slack in reinforcement to facing connections. Inconsistent tensioning of the geosynthetic reinforcement. Localized over compaction
4. Wall out of vertical alignment tolerance (plumbness) or leaning in.	Excessive batter set in panels for select granular backfill material being used. Inadequate compaction of the backfill. Possible bearing capacity failure.
5. Wall out of horizontal alignment tolerance, or bulging.	Backfill material placed wet of optimum moisture content. Backfill contains excessive fine materials (beyond the specifications for percent of materials passing a No. 200 sieve). Backfill material pushed against back of facing panel before being compacted above reinforcing elements. Excessive or vibratory compaction of uniform, medium-fine sand (more than 60 percent passing a No. 40 sieve). Inconsistent tensioning of the geosynthetic reinforcement. Localized over compaction. Backfill saturated by heavy rain or improper grading of backfill after each day’s operations.
6. Panels do not fit properly in their intended locations.	Panels are not level. Differential settlement (see Cause 1). Panel cast beyond tolerances. Failure to use spacer bar.
7. Large variations in movement of adjacent panels.	Backfill material not uniform. Backfill compaction not uniform. Inconsistent setting of facing panels.

Documentation Requirements – 840 MSE Walls

1. Did the panels arrive with a TE-24?

2. Were the panels rejected or repaired as per the specifications?

3. Was the select granular material approved?

4. If the wall was in a cut, were the sidewalls properly protected?

5. Was the foundation properly prepared?

6. Was the drainage properly constructed?

7. Was the filter fabric properly placed?

8. Was the foundation undercut properly constructed?

9. Was the leveling pad placed as specified?

10. Were the wall panels placed according to the plan and markings on the back of the panels?

11. Was external bracing used for the first lift of panels?

12. Were the horizontal and vertical tolerances met?

13. Was the soil reinforcement placed perpendicular to the wall face?

14. Was the SGB placed in 8-inch lifts?

15. Was the backfill compacted to the specification requirements?

16. Was the backfill within 3 feet of the wall compacted to the specification requirements?

17. Did a manufacturer’s representative inspect the site during the wall construction?

18. Did the soils consultant properly take the compaction tests?

19. Was the coping and traffic barrier constructed properly?

20. Were the pile sleeves constructed properly?

21. Perform all the compaction tests according to S-1015 or SS-878.

22. Document on the CA-EW-1,CA-EW-3, CA-EW-8, CA-EW-12, and CA-D-3. Do not duplicate the information on all forms unless necessary.

SUPPLEMENTAL SPECIFICATION 840
MECHANICALLY STABILIZED EARTH WALL

April 19, 2013

840.01 Description

840.02 Definitions

840.03 Materials

840.04 Design and Submittal Requirements

840.05 Fabrication and Acceptance of Precast Concrete Facing Panels

840.06 Construction

840.07 On-Site Assistance

840.08 Method of Measurement

840.09 Basis of Payment

Appendix A – MSE Wall Acceptance Letter

840.01 Description. This work consists of designing for internal stability, preparing shop drawings, and fabricating and constructing a mechanically stabilized earth (MSE) wall using an accredited MSE Wall System. This specification supersedes recommendations by the MSE wall system supplier.

840.02 Definitions. For the purposes of this specification, the following definitions are used:

A. MSE Wall System. A retaining wall system that consists of select granular backfill, reinforcing elements, and facing elements connected to the soil reinforcement.

B. Soil Reinforcement. A material placed within a soil mass to increase the strength of the select granular backfill. Soil reinforcement for MSE walls are typically placed horizontally and consist of steel strips, welded wire mesh, or geosynthetics (polymer mesh or strips).

C. Facing Panels. The component of an MSE wall used to contain the Select Granular Backfill in position at the face of the wall. Facing panels for MSE walls are typically made of precast concrete.

D. Connection Device. The item used to connect the soil reinforcement to the facing panel.

E. MSE Wall System Supplier. The Contractor or Consultant that designs the MSE wall system for internal stability and in accordance with the plans, designs the components of the MSE wall system and prepares the shop drawings.

F. Accredited MSE Wall System. An MSE wall system approved for use by the Office of Geotechnical Engineering. Each accredited MSE wall system has specific designs for the soil reinforcement, facing panels, and connection devices. The following table lists the accredited MSE wall systems and the associated MSE wall system suppliers.

Table 840.02-1

Accredited MSE wall system	MSE wall system supplier
Reinforced Earth	The Reinforced Earth Company
Retained Earth	The Reinforced Earth Company
MSE Plus	SSL, LLC
Tricon Retained Soil	Tricon Precast
ARES	Tensar Earth Technologies
EarthTrac HA	EarthTec
GeoMega	The Reinforced Earth Company
Sine Wall	Sine Wall, LLC

G. Precaster. A manufacturer certified by the Department according to Supplement 1073 to produce precast concrete products. The Precaster furnishes the facing panels for the accredited MSE wall system.

840.03 Materials.

A. Precast Concrete Facing Panels. Furnish materials conforming to the following:

Portland cement................................... 701.02, 701.04, or 701.05

Reinforcing steel................................................................. 709.00

Microsilica.......................................................................... 701.10

Ground granulated blast furnace slag (GGBFS)................ 701.11

Fly ash................................................................................ 701.13

Fine aggregate.................................................................... 703.02

Coarse aggregate................................................................ 703.02

Air-entraining admixture.................................................... 705.10

Chemical admixtures.......................................................... 705.12

B. Soil Reinforcement. Furnish soil reinforcements and connection devices conforming to the requirements for the appropriate accredited MSE wall system listed below. Provide certified test data for all of the requirements. Refer to the shop drawings for the shape and dimensions of soil reinforcements.

Store soil reinforcements off the ground and protect against weather by covering with tarps. Do not bend steel soil reinforcements after galvanizing.

1. Reinforced Earth

Furnish soil reinforcement consisting of steel strips or ladders. Furnish steel strips conforming to ASTM A 572, Grade 65 (ASTM A 572M, Grade 450). Furnish ladders conforming to ASTM A 185 (ASTM A 185M). Furnish soil reinforcement galvanized according to the requirements of ASTM A 123 (ASTM A 123M). Furnish connection devices consisting of tie strips or tie plates conforming to ASTM A 1011, Grade 50 (ASTM A 1011M, Grade 340) and galvanized according to the requirements of ASTM A 123 (ASTM A 123M). Furnish bolts conforming to ASTM A 325 or ASTM A 449. Furnish nuts conforming to ASTM A 563 and washers conforming to ASTM F 436. Furnish bolts, washers and nuts that are galvanized according to the requirements of ASTM F 2329 or ASTM A 153 (ASTM A 153M).

2. Retained Earth

Furnish soil reinforcement consisting of welded wire mesh conforming to ASTM A 185 (ASTM A 185M) and galvanized according to the requirements of ASTM A 123 (ASTM A 123M). Furnish connection devices consisting of clevis loops and connector rods conforming to ASTM A 82 (ASTM A 82M) and galvanized according to the requirements of ASTM A 123 (ASTM A 123M).

3. MSE Plus

Furnish soil reinforcement consisting of welded wire mesh conforming to ASTM A 185 (ASTM A 185M) and galvanized according to the requirements of ASTM A 123 (ASTM A 123M). Furnish connection devices consisting of loop embeds and connecting pins conforming to ASTM A 82 (ASTM A 82M) and galvanized according to the requirements of ASTM A 123 (ASTM A 123M).

4. Tricon Retained Soil

Furnish soil reinforcement consisting of welded wire mesh conforming to ASTM A 185 (ASTM A 185M) and galvanized according to the requirements of ASTM A 123 (ASTM A 123M). Furnish connection devices consisting of panel anchors and locking rods conforming to ASTM A 82 (ASTM A 82M) and galvanized according to the requirements of ASTM A 123 (ASTM A 123M).

5. ARES

Furnish soil reinforcement consisting of high density polyethylene (HDPE) geogrids and connection devices consisting of HDPE geogrids and bodkin bars. Furnish either UX1400MSE, UX1500MSE, UX1600MSE or UX1700MSE geogrids from Tensar Earth Technologies, that conform to the following requirements.

Table 840.03-1

	UX1400MSE	UX1500MSE	UX1600MSE	UX1700MSE
Minimum Tensile Strength ASTM D 6637	4,800 lb/ft (70 kN/m)	7,810 lb/ft (114 kN/m)	9,870 lb/ft (144 kN/m)	11,990 lb/ft (175 kN/m)

6. EarthTrac HA

Furnish soil reinforcement consisting of steel strips conforming to ASTM A 572, Grade 50 (ASTM A 572M, Grade 345) and galvanized according to the requirements of ASTM A 123 (ASTM A 123M). Furnish connection devices consisting of either single lugs conforming to ASTM A 572, Grade 50 (ASTM A 572M, Grade 345) or double lugs conforming to ASTM A 36. Furnish connection devices that are galvanized according to the requirements of ASTM A 123 (ASTM A 123M). Furnish bolts and nuts conforming to ASTM A 325 (ASTM A 325M) and galvanized according to the requirements of ASTM A 153 (ASTM A 153M).

7. GeoMega

Furnish soil reinforcement consisting of high tenacity polyester (HTPET) geosynthetic strips encased in a polyethylene sheath and connection devices consisting of injection-molded polypropylene sleeves. Furnish either GS1, GS2, or GS3 geostraps from The Reinforced Earth Company, that conform to the following requirements.

Table 840.03-2

	GS1	GS2	GS3
Minimum Tensile Strength ASTM D 6637	8.44 kips (37.5 kN)	11.25 kips (50 kN)	14.62 kips (65 kN)

8. Sine Wall

Furnish soil reinforcement consisting of configured steel strips conforming to ASTM A 1011, Grade 65 (ASTM A 1011M, Grade 450) and galvanized according to the requirements of ASTM A 123 (ASTM A 123M).. Furnish connection devices consisting of configured strip connectors conforming to ASTM A 1011, Grade 50 (ASTM A 1011M, Grade 340) and galvanized according to AASHTO M 111 (ASTM A 123). Furnish bolts conforming to ASTM A 325, nuts conforming to ASTM A 563, and washers conforming to ASTM F 436. Galvanize bolts and nuts according to the requirements of either ASTM F 2329 or ASTM A 153 (ASTM A 153M).

C. Bearing Pads. Furnish bearing pads that will provide a long term horizontal joint spacing of at least 3/8 inch (10 mm). Provide bearing pads to the dimensions shown in the shop drawings.

D. Facing Panel Joint Cover. Furnish a woven, 100 percent monofilament, geotextile fabric conforming to AASHTO M 288 Table 1, Class 2 less than 50 percent elongation; with UV stability (retained strength) according to ASTM D4355 of 90 percent after 500 hours, and conforming to AASHTO M 288 Table 2 requirements for less than 15 percent in situ soil passing 0.075 mm sieve. Provide certified test data for the geotextile fabric.

Use an adhesive that secures the fabric to the wall during construction. Use a minimum geotextile fabric width of 18 inches (455 mm). Before installation, protect the geotextile fabric from exposure to direct sunlight.

E. Select Granular Backfill. Furnish select granular backfill (SGB) material conforming to either 703.17, Aggregate Materials for 304, or 703.11, Structural Backfill Type 2, and the requirements listed below.

1. Do not use slag materials or recycled portland cement concrete.

2. Ensure the SGB material has an internal angle of friction equal to or greater than 34 degrees when tested according to AASHTO T 236 and the following requirements:

a. Obtain the test sample from the portion of the SGB material which passes a No. 10 sieve.

b. Determine the maximum dry density and optimum moisture of the test sample according to AASHTO T 99, Method A.

c. Compact the sample for direct shear testing to 98 percent of the maximum dry density and within one percent of optimum moisture content as determined in 840.03.E.2.b.

d. Perform the direct shear test three times at normal stresses of 10, 20, and 40 pounds per square inch (70, 140, 280 kPa).

e. Plot the maximum shear stress versus the normal stress for each test. Draw a straight line that is a best fit to the three points using the least-squares method. Determine the internal angle of friction by measuring the angle of the best fit line from horizontal.

If the internal angle of friction is less than 34 degrees and the SGB has a significant amount of material retained on the No. 10 sieve, then the Contractor may submit an alternate shear test procedure that includes the material larger than the No. 10 sieve in the test sample.

3. For MSE wall systems that use steel soil reinforcements and connection devices, ensure that the SGB material meets the following requirements:

a. A pH between 5.0 and 10.0 when tested according to AASHTO T 289.

b. A resistivity greater than 3000 ohm-cm when tested according to AASHTO T 288. If the SGB material has a resistivity greater than 5000 ohm-cm, the Department will waive testing for chloride and sulfate levels.

c. A chloride level less than 100 ppm when tested according to AASHTO T 291.

d. A sulfate level less than 200 ppm when tested according to AASHTO T 290.

4. For MSE wall systems that use geosynthetic soil reinforcement, ensure that the SGB material meets the following requirements:

a. A pH between 4.5 and 9.0 when tested according to AASHTO T 289

Obtain all acceptance samples from the material stockpile.

Thirty days before the MSE wall construction, provide certified test data from an independent testing laboratory that verifies the SGB material meets all requirements. The Engineer will conditionally accept the SGB material based upon a visual inspection of the SGB material and a review of the certified test data. Final acceptance of SGB material will be based on testing of quality assurance samples by the Department to verify that the certified test data is accurate. The Engineer will sample the SGB material when the SGB material is delivered to the project before it is placed in the MSE wall. The Engineer will provide the sample and the certified test data to the Office of Materials Management.

F. Backfill Drainage Material. Furnish materials conforming to:

Plastic Pipe......................................................................... 707.33

Filter Fabric, Type A.......................................................... 712.09

Furnish porous backfill consisting of gravel or stone with a No. 57 size gradation according to Table 703.01-1. Use material with a sodium sulfate soundness loss less than 15 percent (5 cycle) when tested according to AASHTO T 104.

Furnish bedding and backfill for non-perforated pipe consisting of natural sand, gravel or sand manufactured from stone conforming to 703.11, Structural Backfill Type 2, except 100 percent of the material shall pass through a ¾-inch (19.0 mm) sieve.

For perforated pipe installed within the SGB, the Contractor may furnish fabric-wrapped perforated pipe instead of wrapping filter fabric around the perforated pipe in the field. The fabric-wrapped perforated pipe must come from the supplier with the filter fabric completely surrounding the pipe and securely attached to the pipe. Ensure that the pipe and filter fabric meet the above requirements. The Department will accept certified test data for the filter fabric on fabric-wrapped perforated pipe in place of NTPEP test data.

G. Foundation Preparation Materials.

Furnish crushed carbonate stone, gravel, durable sandstone, durable siltstone, or granulated slag conforming to 703.16.C, Granular Material Type C.

H. Concrete Coping. Furnish materials conforming to:

Concrete, Class QC-1.............................................................. 499

Epoxy coated reinforcing steel........................................... 709.00

Preformed expansion joint filler......................................... 705.03

I. Leveling Pad. Furnish Class QC-1 Concrete according to Item 511.

J. Concrete Sealer. Furnish epoxy-urethane sealer conforming to 705.23.A.

K. Pile Sleeves Materials.

1. Plastic Pipe. Furnish corrugated polyethylene smooth lined pipe conforming to either 707.33 or ASTM F 2648, or PVC corrugated smooth interior pipe conforming to 707.42. Furnish sleeves with an inside diameter at least 2 inches (50 mm) greater than the pile’s diameter or diagonal dimension.

If furnishing plastic pipe manufactured from recycled polyethylene, submit certified test data that shows the pipe conforms with ASTM F 2648. Clearly mark all pipe manufactured from recycled polyethylene so that it is used only for pile sleeves on the project.

2. Granular Fill. Furnish granular material conforming to 703.11, Structural Backfill Type 2, except 100 percent of the material shall pass through a ¾-inch (19.0 mm) sieve.

L. Natural Soil. Furnish A-4a, A-6 or A-7-6 natural soil meeting the requirements of 203.02.I.

840.04 Design and Submittal Requirements.

A. Design Requirements. Design the MSE wall conforming to the requirements listed below and either Section 5.8 of the AASHTO Standard Specifications for Highway Bridges, 17^th edition, 2002, (AASHTO 2002) or Section 11.10 of the AASHTO LRFD Bridge Design Specifications, (AASHTO LRFD). Use the same version of the AASHTO design specifications as used to develop the plans. In the event of a conflict between this specification and the AASHTO specification, this specification will govern.

1. Only use an accredited MSE wall system.

2. Unless a longer minimum soil reinforcement length is given in the plans, provide soil reinforcement with a length that is equal to 70 percent of the wall height but not less than 8 feet (2.4 m). If the wall will be located at an abutment, measure the wall height from the top of the leveling pad to the profile grade elevation at the face of the wall. For all other walls, measure the wall height from the top of the leveling pad to the top of the coping.

3. Use the following soil parameters in the design. These parameters are not to be used for material acceptance.

Table 840.04-1

Fill Zone	Type of Soil	Design Soil Unit Weight	Friction Angle	Cohesion
Reinforced Soil	Select Granular Backfill	120 lbs/ft^3 (18.9 kN/m^3)	34º	0
Retained Soil (Soil behind the Reinforced Soil Zone)	On-site soil varying from sandy lean clay to silty sand	120 lbs/ft^3 (18.9 kN/m^3)	30º	0

4. Use the simplified method or the coherent gravity method for internal stability calculations. The coherent gravity method as described in AASHTO LRFD may also be used for a design otherwise conforming to AASHTO 2002.

5. Include a live load surcharge of 250 psf (12.0 kPa) unless the backfill above the wall is sloped steeper than 4H:1V. Include a live load surcharge even if there is an approach slab at the bridge abutment.

6. Assume a water level within the reinforced soil at the invert elevation of the drainage pipe.

7. Use the following reduction factor values for geosynthetic soil reinforcement.

Table 840.04-2

		Reduction Factors
Accredited MSE Wall System	Soil Reinforcement	Installation Damage RFID	Creep RFCR	Durability RFD
ARES	UX1400MSE UX1500MSE UX1600MSE UX1700MSE	1.25	2.59 2.59 2.59 2.63	1.1
GeoMega	GS1, GS2, GS3	1.1	1.64	1.14

8. Provide a design life of 100 years.

9. Use a 9-foot (2.75 m) minimum length of wall between leveling pad elevation changes. Design the facing panel overhang at the end of the leveling pad of less than 6 inches (150 mm). Do not design vertical steps in the leveling pad greater than 2.5 feet (0.75 m).

10. Use standard panels with maximum dimensions of 5 ft high × 10 ft wide (1.52 × 3.05 m). Special panels along the top and bottom of the wall may have maximum dimensions of 7 ft high × 10 ft wide (2.13 × 3.05 m)

11. Use a separate corner element when two wall sections meet with an interior angle of 130 degrees or less. Do not place two facing panels next to each other with an interior angle of 130 degrees or less. Design the corner element to overlap the adjoining facing panels. Attach soil reinforcements to the corner element.

12. Design the wall to provide a coping as shown on the plans. Provide joints in the coping no more than every 20 feet (6 m) along the length of the wall. Locate coping joints to align with the joints between facing panels.

13. Do not provide a design that bends steel strips or geosynthetic strips. Splaying steel strips up to 15 degrees and geosynthetic strips up to 5 degrees from perpendicular to the facing panel without bending in order to avoid obstacles in the reinforced soil zone is acceptable. Otherwise, provide a special design to avoid the obstacle, such as a structural frame or attaching steel angles to panels. Show the details of the special design in the shop drawings

B. Submittal of Shop Drawings and Calculations. Prepare design calculations according to the above requirements. Prepare shop drawings and include at least the following information in the shop drawings:

1. A site plan for the full length of the retaining wall that shows:

a. Station and offset at the face of the wall measured from the centerline of construction for the ends of the wall and any changes in wall alignment, obtained from the contract documents.

b. Horizontal and vertical curve data for curved walls as outlined and shown on the contract documents.

c. Limits of soil reinforcement.

d. All obstructions to the soil reinforcement, such as piling or catch basins.

2. An elevation view for the full length of the retaining wall that shows:

a. Location of each individually labeled facing panel.

b. Elevations at the ends of the wall and any changes in elevation at the top or bottom of the wall.

c. Required soil reinforcement lengths and locations.

3. Representative cross-sections at each design change.

4. Design details to avoid obstacles in the reinforced soil zone, such as splaying, panel steel angles or structural frames.

5. Shop drawings for fabrication of the facing panels that show:

a. The Precaster who will produce the facing panels.

b. Minimum concrete compressive strength at 28 days and for form removal.

c. Dimensions and tolerances.

d. Soil reinforcement connection details and locations in the facing panels.

e. Reinforcing steel locations, sizes, lengths, type and bending diagrams.

f. Aesthetic surface treatment details.

g. If the plan design calls for MSE Wall alignment on a horizontal curve, then chamfer the back panels along the back vertical joints to maintain the front panel joint tolerance in 840.06.G.

6. Wall drainage details, including:

a. Location and elevation of drainage pipe and outlets, obtained from the contract documents.

b. Locations and details of any required penetrations in the facing panels, obtained from the contract documents.

7. Actual bearing pressures.

8. Allowable bearing capacity, obtained from the contract documents.

9. Design life.

10. Angle of internal friction used for the design.

11. Construction manual for the accredited MSE wall system.

12. Revised quantity of select granular backfill based on the length of soil reinforcement used in the design. Compare revised quantity to the estimated quantity of select granular backfill in the plans and indicate the difference.

Only include details, notes, panel types, and other items on the shop drawings that apply to the project. Do not include generic details, notes, or designs for standard panel types that are not used on the project.

Use an Ohio Registered Engineer to prepare, sign, seal and date the shop drawings, design calculations and acceptance letter provided in Appendix A. Use a second Ohio Registered Engineer to check, sign, seal and date the shop drawings, design calculations and acceptance letter provided in Appendix A.

Submit two copies of the shop drawings, design calculations and acceptance letter to the Engineer at least 15 days before any part of wall construction begins. Submit drawings on 11´17 inch paper, and calculations on 8½´11 inch paper. Also submit drawings and calculations in electronic tiff format. The Engineer will submit the drawings, calculations and acceptance letter to the Office of Construction Administration.

Ensure all submittals meet the requirements for materials, design, and construction. Ensure all required field measurements are made and included in the drawings. Coordinate all details of the work to be performed by other entities on the project. The Department will not make allowance for additional cost or delays to the Contractor for incorrect fabrication as a result of failure to perform this coordination.

Department acceptance of the submittal does not relieve the Contractor or the MSE wall system supplier from responsibility for errors and omissions found after acceptance of the submittal.

840.05 Fabrication and Acceptance of Precast Concrete Facing Panels. Provide precast concrete facing panels from a precast concrete producer certified under Supplement 1073. Do not start facing panel fabrication until the shop drawings and design calculations have been accepted by the Department.

A. Concrete Proportioning. Proportion a concrete mix design that provides the minimum compressive strength required in the shop drawings and the minimum over design of ACI 318 and conforms to the air content requirements of Supplement 1073.

B. Form Inspection. Before casting, measure all forms for tolerances defined in 840.05.G and document the measurements. Reject any forms not within tolerances.

C. Casting. Before casting, place the reinforcing steel, soil reinforcement connection devices, lifting elements, and coping dowels at the locations shown on the shop drawings and to the tolerances specified below. Design the lifting elements to eliminate concrete spalling during handling. Cast the panels on a flat area, with the front face down. Use clear form oil approved by the MSE wall system supplier and do not substitute the form oil after the casting operation begins.

Leave all forms in place until the concrete panel can be removed without damage. Use the shop drawings to define the minimum compressive strength required for form removal. Test and record the strength of the concrete before removing the forms.

D. Curing. Use the curing method recommended by the MSE wall system supplier. Cure the concrete sufficiently to develop the minimum compressive strength required in the shop drawings.

E. Concrete Testing. During facing panel production, randomly sample the concrete and test according to ASTM C 172 and Supplement 1073. A single compressive strength sample consists of at least four test cylinders for each production lot. A production lot is either 40 panels or a single day’s production, whichever is less. Perform compressive strength testing according to Supplement 1073.

F. Concrete Finish and Aesthetic Treatment. If an aesthetic surface treatment is shown in the plans or shop drawings, cast it into the front face of the panels. If an aesthetic surface treatment is not required, finish the front face of the panels to a smooth surface. Finish the back face of the panels to a uniform surface, free of open pockets of aggregate. Ensure that both faces conform to the tolerances specified below.

G. Panel Dimensions and Tolerances. Fabricate the panels with a minimum thickness of 5 ½ inches (140 mm). The minimum thickness does not include the aesthetic surface treatments. Use the tolerances in Table 840.05‑1.

Table 840.05-1

	Tolerance
Panel dimensions	± 1/8 in. (3 mm)
Panel squareness (difference between two diagonals)	± 1/4 in. (6 mm)
Panel thickness	± 1/8 in. (3 mm)
Location of soil reinforcement connection device	± 1/4 in. (6 mm)
Panel surface (size of surface defect measured over a length of 5 ft (1.5 m)) Smooth formed finish Textured finish	± 1/8 in. (3 mm) ± 5/16 in. (8 mm)
Position of reinforcing steel	± 1/8 in. (3 mm)

Inspect and document that the panels are dimensionally correct; that the soil reinforcement connection devices are at the locations shown on the shop drawings; that the panel finishes are correct; that concrete’s form removal and final strength meet shop drawings; and that all tolerances have been met.

H. Precast Panel Rejection, at the plant and field site. Reject panels having any of the following:

1. Defects that indicate imperfect molding.

2. Defects that indicate honeycombed or open texture concrete.

3. Defects in the physical characteristics of the concrete, or damage to the aesthetic surface treatments.

4. Concrete chips or spalls that exceed 4 inches (100 mm) wide or 2 inches (50 mm) deep. Repair all chips and spalls that are smaller.

5. Stained form faces, due to form oil, curing or other contaminants.

6. Signs of aggregate segregation.

7. Cracks wider than 0.01 inch (0.25 mm) or penetrating more than 1 inch or longer than 12 inches (300 mm).

8. Facing panels that do not meet the specified tolerances.

9. Damaged soil reinforcement or connection devices, including connection devices bent more than 15 degrees.

10. Unusable lifting inserts.

11. Exposed reinforcing steel.

12. Insufficient concrete compressive strength.

13. Missing coping dowels.

I. Panel Markings. Permanently mark the back surface of each panel with the date of manufacture, the panel identification from the shop drawings, the production lot number, and the precaster’s inspection and acceptance mark. The precaster’s marks represent the panel meets all specification requirements.

The precaster shall maintain record fabrication drawings according to Supplement 1073 and this specification for each panel design produced.

J. Handling, Storing and Shipping Panels. Handle, store, and ship panels to avoid chipping, cracking and fracturing the panels; excessive bending stresses; and damaging the soil reinforcement connection devices. Support panels on firm blocking while storing and shipping.

Do not ship panels until concrete has attained the required compressive strength.

Submit 840.05.G shipment documentation to the Engineer as the facing panels are delivered to the project along with the TE-24 shipping document.

840.06 Construction.

A. MSE Wall Preconstruction Meeting. Request a meeting at least 15 days before wall construction begins and after the Department has accepted the shop drawings and design calculations. Have a representative from the accredited MSE wall system supplier attend the meeting. Provide a complete written sequence of construction at the meeting and review the sequence, any construction issues, the specifications and the accredited MSE wall system requirements. Determine any issues that need to be resolved for construction. Resolve those issues.

During the MSE wall preconstruction meeting, request sampling of the SGB for verification acceptance.

B. Facing Panel Inspection. Inspect all facing panels for any damage and reject panels according to 840.05.H. Provide acceptable replacement panels for any panels rejected. Either replace panels or document the damage and propose to the Engineer a complete repair method for the damaged panel.

C. Wall Excavation. Excavate to the limits shown in the plans. Remove unsuitable foundation soils to the limits shown in the plans. Wall excavation is unclassified and includes any rock or shale encountered. Dewater the excavation if water is encountered. Develop and implement a plan to protect the open excavation from surface drainage during construction and until the wall is placed. Protect the excavation against collapse. Dispose of materials not required or suitable for use elsewhere on the project.

D. Foundation Preparation. Level the bottom of the excavation. The Department will inspect the foundation to verify that the subsurface conditions are the same as those anticipated during the design.

After the foundation has been accepted, spread, place and compact 12 inches (300 mm) of granular material type C according to the requirements of 204.07.

E. Leveling Pad Construction. Construct the concrete leveling pad using unreinforced, cast-in-place concrete. Do not use precast leveling pads. The leveling pad shall be 6 inches (150 mm) thick and 24 inches (610 mm) wide. Cure the concrete and do not start wall erection until specimen beams have attained a modulus of rupture of 400 pounds per square inch (4.2 MPa).

Construct all leveling pads so the top of the pad is within 1/8 inch (3 mm) of the elevation shown on the shop drawings. Construct the pads so the surface does not vary more than 1/8 inch in 10 feet (3 mm in 3 m). Check the leveling pad construction before wall erection and report the elevations and surface variation to the Engineer.

If the design calls for a change in the leveling pad elevation (i.e. steps), then construct the leveling pad so the facing panel extends no more than 6 inches (150 mm) beyond the end of the leveling pad.

F. Wall Drainage. Install drainage as shown on the plans. Use perforated pipe within the wall limits and non-perforated pipe outside the wall limits. Provide banded or sealed joints. Slope the drainage pipe to provide positive drainage. If it is not possible to outlet the drainage pipe, then notify the Engineer.

Where perforated pipe is surrounded by select granular backfill (SGB), use fabric-wrapped perforated pipe or wrap the filter fabric around the perforated pipe, overlapping the ends of the filter fabric at least 9 inches (230 mm). Porous backfill is not required in these locations.

Where perforated pipe is located outside the limits of the SGB, completely surround the perforated pipe with porous backfill. Provide at least 2 inches (50 mm) of porous backfill on all sides of the perforated pipe. Vibrate, tamp, or compact the porous backfill to approximately 85 percent of the original layer thickness. Completely wrap the porous backfill with filter fabric to prevent piping. Use a 1 foot (0.3 m) overlap for the filter fabric.

Place and compact the bedding and backfill material for non-perforated pipe according to Item 611.

If water collects in the excavation at any time, then remove the water from the excavation immediately.

G. Wall Erection. Place facing panels in the sequence shown on the shop drawings. Lift panels using the lifting devices set into the upper edge of each panel. Place the initial row of panels on the centerline of the leveling pad and level the panel. Use shims to level the panels. If the shim height is greater than 3/8 inch (10 mm) start the erection over. Do not use bearing pads to level the panels. Do not install panels that overhang the leveling pad transversely. Reconstruct the leveling pad if the panels are transversely overhanging.

Facing panels are allowed to extend beyond the end of the leveling pad up to 6 inches (150 mm) when the leveling pad changes elevation. Fill the void with SGB immediately after the first row of panels are set, wedged, braced and clamped.

Starting with the second row of panels, install at least two bearing pads per panel, uniformly spaced, to properly construct the panels’ horizontal joint. After each panel has been placed, ensure the panel is horizontally level.

Construct the panels so the horizontal and vertical joints are ½ to 1 inch (13 to 25 mm) wide. Use ¾ inch (19 mm) spacers to control the joint spacing. Once the joint spacing is achieved, record the joint gap on the shop drawings and present this information to the Engineer once a week. If the required joint spacing is not achieved, then make the required corrective action.

The Engineer will hold a flashlight perpendicular to the facing panel to determine if the fabric is exposed. If the fabric is exposed, then the joint is unacceptable. Submit a repair method to the Department for protecting the fabric.

Initially, batter the panels back an appropriate amount so that the final vertical position is achieved.

Use external bracing as necessary to stabilize and batter the first panel lift and any other panel lifts requiring external stability. Place panels and backfill in successive horizontal lifts according to the sequence shown on the shop drawings.

Once the panels have been erected and the SGB placed to a height matching the outside proposed ground elevation, fill the outside embankment immediately. Follow the requirements of Item 203 for this work. If water has ponded in front of the wall, then pump the water out prior to constructing the embankment.

Maintain the panels in their vertical and battered position by means of temporary wood wedges and clamps placed at the panel joints. Check vertical tolerances with a 6-foot (2 m) level. Check the panel to panel horizontal tolerance with a 6-foot (2 m) straightedge. Do not release the panel from the lifting device until the position of the panel has been checked and the wedges and clamps are in place.

After compacting the backfill behind each row of panels, check the horizontal and vertical alignment of the wall and make adjustments as required. Remove the clamps prior to placing the next row of panels and after the vertical and horizontal alignment is checked.

Do not exceed a vertical and horizontal alignment tolerance of 1/2 inch (13 mm) at any point along a 10-foot (3 m) straight edge placed against the wall. Do not construct any panel more than 1/2 inch (13 mm) out of vertical or horizontal alignment from the adjacent panels. Do not exceed the final overall vertical tolerance of the wall (plumbness from top to bottom) of ½ inch (13 mm) per 10 feet (3 m) of wall height. Starting with the third row of panels, use a plumb bob to check the overall vertical tolerances for every panel. Continuously monitor the batter, alignment and tolerances. Make adjustments as required. For portions of a wall over 30 feet (9 meters) in height, record the plumbness measurement for each panel on the shop drawings and present this information to the Engineer once a week.

Do not pull on the soil reinforcement to align the panels.

Remove the wedges as soon as the second panel above the wedged panel is completely erected and backfilled.

Install the geotextile fabric strip over each horizontal and vertical panel joint. Center the fabric over the joint. Use a minimum 12-inch (300 mm) lap between cut sections of the fabric. Clean the concrete to remove dirt by using a brush before applying the adhesive and fabric. Place the fabric so it covers the horizontal and vertical joints by 6 inches (150 mm) on each side of the joint. Attach the fabric to the back of the facing panel using an adhesive that securely bonds the fabric to the facing panel. Apply adhesive to the wall or the fabric for the full perimeter of the installed length and width of the geotextile strip. Follow the adhesive manufacturer’s temperature recommendations.

When the fabric is placed around a slip joint, allow some horizontal slack in the fabric to allow for movement.

H. Soil Reinforcement Installation. Place the soil reinforcement perpendicular to the facing panel unless otherwise shown on the shop drawings. If steel soil reinforcement cannot be placed perpendicular to the wall, then it may be splayed up to 15 degrees. The transverse wires of welded wire mesh may be cut in order to splay the soil reinforcement. If more than a 15 degree splay is required to place the soil reinforcement, then a special design is required on the shop drawings. If a situation is encountered in the field that was not accounted for on the shop drawings, notify the Engineer.

If bolts are used to connect the soil reinforcement to the facing panel, then place the bolts in the connection from the bottom and attach the washer and nut. Tighten the bolt with a wrench or socket.

If loops and a pin are used to connect the soil reinforcement to the facing panel, then place the pin through all of the loops. Place wooden wedges between the pin and the panel to remove any slack in the connection. Ensure the pin and loops are in contact with each other.

Before placing SGB over the soil reinforcements ensure that:

1. The soil reinforcement matches what is shown on the shop drawings.

2. The soil reinforcement is continuous from the panel to the end of the reinforced soil zone.

3. The soil reinforcement is connected to the panel correctly. Replace the panel if necessary to correctly connect the soil reinforcement.

4. For geosynthetic reinforcements ensure the soil reinforcement is pulled taut to eliminate wrinkles or folds and held in place during placement of the SGB.

Do not cut or splice steel soil reinforcements. Do not operate equipment directly on the soil reinforcements.

I. Select Granular Backfill Placement. Transport and handle the Select Granular Backfill (SGB) in a manner that minimizes the segregation of the material. Use the following procedure for placing and compacting the SGB.

1. Place and compact the initial lifts of SGB until it is about 2 inches (50 mm) above the connection for the bottom layer of soil reinforcement. For MSE wall systems that use steel soil reinforcement or geosynthetic strips, do not place SGB against the initial row of panels yet. This is Item 1 in Figure 840.06-1. For MSE wall systems that use geogrid soil reinforcements, place the SGB against the initial row of panels and lightly compact it.

Figure 840.06-1 Backfilling for the First Row of Panels Only
(MSE wall systems that use steel soil reinforcement or geosynthetic strips)

2. Connect the soil reinforcement and place an 8-inch (200 mm) loose lift of SGB on top of it (Item 2 in Figure 840.06-1). Place and compact the SGB at least 3 feet (1.0 m) away from the facing panels and moving parallel to the panels. Continue to place and compact the lift of SGB with additional passes moving away from the panels towards the free end of the soil reinforcement. See Figure 840.06-2.

3. Place SGB between the initial row of facing panels and the previously placed SGB. Place the SGB in one lift until it is about 8 inches (200 mm) above the soil reinforcement (Item 3 in Figure 840.06-1). Compact the material with six passes of a mechanical tamper or vibratory plate compactor that applies an impact or centrifugal force between ½ to 2 tons (0.6 to 2.2 metric tons). Do not perform compaction testing on the material within 3 feet (1.0 m) of the facing panels.

4. Place and compact additional lifts of SGB at least 3 feet (1.0 m) away from the facing panels and moving parallel to the panels. Continue to place and compact each lift of the SGB with additional passes moving away from the panels towards the free end of the soil reinforcement. See Figure 840.06-2.

Figure 840.06-2 Procedure for SGB Placement and Compaction (Plan View)

5. Place and compact SGB in the 3-foot (1 m) area between the facing panels and the previous lift of SGB. Compact the material with six passes of a mechanical tamper or vibratory plate compactor that applies an impact or centrifugal force between ½ to 2 tons (0.6 to 2.2 metric tons). Do not perform compaction testing on the material within 3 feet (1.0 m) of the facing panels.

Figure 840.06-3 SGB Placement and Compaction Next to Facing Panels (Plan View)

Figure 840.06-4 SGB at Connection

6. When the SGB reaches the next layer of soil reinforcement, place the SGB that is more than 3 feet (1 m) away from the facing panels to a level 2 inches (50 mm) above the soil reinforcement connection. Slope the SGB that is within 3 feet (1 m) of the facing panels as shown in Figure 840.06-4.

7. Repeat steps 4 through 6 until placement of the SGB and soil reinforcements is complete.

Except as stated otherwise in the procedure above, place and compact the SGB as follows. Place the SGB in loose lifts no greater than 8 inches (200 mm) thick. Compact SGB using a vibratory roller with a static weight between 6 to 10 tons (7 and 11 metric tons). Operate compaction equipment in a direction parallel to the facing panels. Test the compaction according to Supplement 1015. Use either Test Section Method A or B according to Supplement 1015 and 203.07. Sample the SGB material and create a moisture density curve according to AASHTO T 99, Method C for each type and source of material. Compact the SGB to a minimum of 98 percent of the test section maximum dry density.

Do not disturb, damage, or distort soil reinforcements, facing panels or joint coverings during compaction.

At the end of each day’s operations, shape the last lift of SGB to direct rain water runoff away from the wall face. Prevent surface drainage from adjacent areas from entering the wall construction site.

J. Pile Sleeves. When piles are located within the reinforced soil zone, install pile sleeves during MSE wall construction. Place the bottom of the sleeves at the bottom of the SGB or at the bottom of the undercut whichever is deeper. Maintain the vertical alignment of the pile sleeve during construction of the MSE wall. After driving the pile, place granular fill into the sleeve around the pile in a uniform manner so there are no unfilled voids within the pile sleeve.

K. Coping. Cast the coping in place according to Item 511 and the plans. If using anchors installed in precast panels to support the formwork for the coping, ensure that the anchors are at least 6 inches (150 mm) from the edge of the precast panel. Do not use precast concrete coping. When the panels have an aesthetic surface treatment, use expanding foam to fill the voids between the facing panel and the forms for the coping. Remove any visible foam after the concrete coping has cured.

L. Concrete Sealing. Seal exterior surfaces of all panels and coping with an epoxy-urethane sealer according to Item 512 after the completion of wall construction. Do not damage the fabric covering the panel joints when preparing the surface before applying the sealer.

M. Natural Soil Placement. Once the SGB and the coping are completed, place the natural soil along the slope in 12-inch (300 mm) loose lifts. The Department will use 95 percent of the standard Proctor maximum dry density for compaction acceptance.

N. Inspection and Compaction Testing. Perform all of the work described in SS 878 Inspection and Compaction Testing as it pertains to MSE walls. Hire compaction personnel described in Section 878.02 of Supplemental Specification 878 Inspection and Compaction Testing of Unbound Materials. Provide a summary report of all inspections, compaction tests and measurements every 2 weeks to the Engineer. Include all inspections, measurements, compaction test forms, test section data, failing tests and lots and moisture checks. Notify the Engineer when each lift is complete and provide the compaction test data. The Engineer will perform quality assurance (QA) density tests on every fifth lift. Make the required correction when QA tests fail.

840.07 On-Site Assistance. Have a representative from the accredited MSE wall system supplier provide on-site technical assistance for the number of days shown in the contract. This is done to ensure that the Contractor and the Engineer understand the recommended construction procedures for the accredited MSE wall system.

840.08 Method of Measurement. The Department will measure the Mechanically Stabilized Earth Wall by the number of square feet (square meter). The Department will determine the area of the MSE wall from plan dimensions using a length measured along the outside of the uppermost facing panels and a height from the top of the concrete leveling pad to the top of the concrete coping. The Department will not adjust pay quantities for variations in the concrete leveling pad elevations required to accommodate actual panel placement.

The Department will measure Aesthetic Surface Treatment by the number of square feet (square meters). If all facing panels have an aesthetic surface treatment, the measurement for the aesthetic surface treatment will be the same as for the MSE wall. If the aesthetic surface treatment is applied to only a portion of the facing panels, then the Department will determine the area of Aesthetic Surface Treatment by the total area of the facing panels with the aesthetic surface treatment applied.

The Department will measure Natural Soil, Wall Excavation and SGB by the number of cubic yards (cubic meters) according to 203.09.

The Department will measure Foundation Preparation by the number of square yards (square meters).

The Department will measure the 6" Drainage Pipe Perforated and Non-Perforated by the number of feet (meters) installed and accepted. The Department will not measure the backfill or filter fabric for the drainage pipe for payment. Include this cost in the drainage pipe.

The Department will measure Concrete Coping by the number of feet (meters) as measured along the outside of the uppermost facing panels.

840.09 Basis of Payment. The Department will pay for all of the work described in 840.03.G and 840.06.D under Foundation Preparation.

The Department will pay lump sum Select Granular Backfill (SGB) Inspection and Compaction Testing as follows:

Upon approval of the project personnel 10%

Uniform Progress Payments 80%

Wall Completion 10%

The Department will pay for epoxy-urethane sealer, concrete traffic barrier and sealers placed on traffic barriers under separate pay items.

Payment for wall excavation includes dewatering and disposal of materials. If a separate pay item for Cofferdams and Excavation Bracing is not included in the Contract, the Department will pay for cofferdams and excavation bracing under the contract unit price for the MSE wall.

Payment for MSE wall includes facing panels, soil reinforcements, connection devices, bearing pads, joint covering, pile sleeves, leveling pads, and other items which do not have separate pay items but are necessary to complete the MSE wall.

The Department will pay for accepted quantities at the contract prices as follows:

Item Unit Description

840 Square Foot Mechanically Stabilized Earth Wall

(Square Meter)

840 Cubic Yard Wall Excavation

(Cubic Meter)

840 Square Yard Foundation Preparation

(Square Meter)

840 Cubic Yard Select Granular Backfill

(Cubic Meter)

840 Cubic Yard Natural Soil

(Cubic Meter)

840 Foot (Meter) 6" Drainage Pipe, Perforated

840 Foot (Meter) 6" Drainage Pipe, Non-Perforated

840 Foot (Meter) Concrete Coping

840 Square Foot Aesthetic Surface Treatment

(Square Meter)

840 Days On-Site Assistance

840 Lump Sum SGB Inspection and Compaction Testing

SS 840 Appendix A

MSE Wall Acceptance Letter

Project No.

Wall No.

Name of Accredited MSE Wall System

Design Data
Design Life	100 years
Angle of Internal Friction – Reinforced Soil Zone	34 degrees
Actual Bearing Pressure at base of reinforced soil mass
Allowable Bearing Pressure at base of reinforced soil mass (Reproduced from project plans)

We hereby certify that the design calculations for the internal stability of the mechanically stabilized earth retaining structure and the detail drawings included in this construction submission are in complete conformance with the MSE wall Supplemental Specification 840 and either the AASHTO Standard Specifications for Highway Bridges, 17th Edition, 2002 or the AASHTO LRFD Bridge Design Specifications, 4th edition. We further certify that the design data provided above and data assumed for the design calculation submitted herein is accurate for the above referenced wall.

Engineer’s Seal	Engineer’s Seal
Signature:	Signature:
Date:	Date:

(Provide an MSE Wall Acceptance Letter for each wall designated in the project plans.)