626Mechanically Stabilized Embankment Retaining Walls

Embankment Retaining Walls

626.1General Description

This specification covers the required materials, fabrication, construction, measurement, and payment for mechanically stabilized embankment retaining walls. The scope of work of wall erection includes: • Grading for wall construction • Compacting the wall foundation • General and local dewatering as necessary • Constructing leveling pads • Erecting precast panels • Placing soil reinforcing devices • Placing and compacting special embankment backfill within the reinforced volume • Furnishing and placing precast or cast-in-place concrete coping and cast-in-place or precast traffic barrier on top of the wall if shown on the Plans The wall foundation includes areas underlying the leveling pad and the reinforced volume. Ensure that items used to construct the mechanically stabilized embankment retaining walls but not mentioned in this specification conform to the applicable sections of the Standard Specifications. Ensure that the architectural treatment of the precast panels is according to the plan details. For patented mechanically stabilized embankment retaining walls, obtain panels, soil reinforcing devices, connecting devices, joint materials, attachments, and expertise to construct the walls. 626.1.01 Definitions Wall foundation—the area underlying the leveling pad and the reinforced volume. 626.1.02 Related References

1046 1046 1046 1046 1046

AASHTO M 243 AASHTO T 22 ASTM A 82 ASTM A 123/A 123M ASTM A 153/A 153M ASTM A 185 ASTM A 307 ASTM A 325 (ASTM A 325M) ASTM A 563 ASTM A 570/A 570M ASTM A 709 (ASTM A 709M) ASTM B 695 ASTM D 2240 ASTM F 463 (ASTM F 463M) GDT 7 GDT 24a GDT 24b GDT 35 GDT 75 QPL 9 QPL 58 Standard Operating Procedure 3, Precast/Prestressed Concrete Bridge Members 1992 AASHTO Specifications for Highway Bridges, Section 18, Elastomeric Bearings 626.1.03 Submittals General Provisions 101 through 150.

626.2Materials

Use tie strips shop-fabricated of hot rolled steel that conform to the minimum requirements of ASTM A 570 Grade 50 (ASTM A 570M Grade 345). Hot roll reinforcing strips from bars to the required shape and dimensions. Their physical and mechanical properties shall conform to ASTM A 709 Grade 36 (ASTM A 709M Grade 250).

Use soil reinforcing mesh shop-fabricated of cold drawn steel conforming to the minimum requirements of ASTM A 185. 1047 1047 1047 1047 1047

Use Backfill Stabilizing Geogrid that conforms to the requirements of Section 809.

Use high-strength bolts and nuts that are hexagonal cap screw and that conform to ASTM A 325(A 325M), galvanized. Ensure that they are of the diameter shown in the plans—1-1/2 in. (40 mm) long with 3/4 in. (20 mm) thread length. Use galvanized washers with galvanizing fastener elements conforming to ASTM A 153/A 153M.

Use materials that conform to the following standards: Material Conforms to the Requirements of: Steel strap connection bar and plate ASTM A 709 Grade 36 steel (ASTM A 709 Grade 250) Bolts ASTM A 307 (ASTM A 307M) Nuts ASTM A 563 Washers ASTM F 436 (ASTM F 436M) Coatings for connecting devices As specified in the Subsection below

welded according to ASTM A 185. Ensure that they develop a stress of at least 0.9 times the steel’s yield strength. Use loops galvanized according to ASTM A 153/A 153M, Class B 3, or ASTM A 123/A 123M.

galvanized according to ASTM A 123/A123M.

meeting the same physical and chemical properties as the backfill stabilizing geogrid.

Use Class AA concrete for precast panels, except ensure that the 28-day strength is at least 4,000 psi (28 MPa). Except as indicated in the approved mix design, admixtures will not be allowed. Do not use admixtures containing chlorides. Use Class A concrete for leveling pads, traffic barriers, and coping. 1048 1048 1048 1048 1048

Treat joints between panels as listed in this Subsection. In flood plains or other intermittently inundated areas, cover the different joint types as follows: Joint Type Action Joints between panels from an elevation 3 ft. (1 m) above the 100-year flood elevation to the bottom of the wall Cover on the back side of the wall with a woven plastic filter fabric sheet. Joints between panels from 3 ft. (1 m) above the 100-year high water elevation to the top of the wall Cover on the back side of the wall with a woven or nonwoven plastic filter fabric sheet. All other locations Cover joints between panels with a woven or nonwoven plastic filter fabric sheet Place in horizontal joints between panels two 4 inch by 3 in. by ¾ in. (100 mm by 75 mm by 20 mm) ribbed bearing pads or elastomeric pads as specified on the plans. Use ribbed bearing pads made of SBR rubber with a durometer hardness of 80 plus or minus 10 as determined by ASTM D 2240. Use elastomeric pads that are 100% virgin chloroprene (neoprene) and meet the requirements of the 1992 AASHTO Specifications for Highway Bridges, Section 18, Elastomeric Bearings. Caulk the openings on either side of and between the pads with 2 in. by 2 in. (50 mm by 50 mm) open-cell urethane foam strips or equal as approved by the Engineer in addition to any other joint treatment that is required. Caulk vertical joints with 2 in. by 2 in. (50 mm by 50 mm) open-cell urethane foam strips. Piece the urethane foam strips together with a minimum overlap of 4 in. (100 mm). Use plastic filter fabric sheets with a minimum width as follows: For Vertical Joints 18 inches (450 mm) wide For Horizontal Joints 12 inches (300 mm) wide Overlap the joint with the filter fabric by at least 4 in. (100 mm). When piecing together the filter fabric, overlap by at least 4 in. (100 mm). Glue the filter fabric to the panels using any adhesive on the Qualified Products List (QPL). Use any woven and nonwoven plastic filter fabric listed on the QPL for work in this Specification, subject to the above requirements.

Use material in the MSE Wall Backfill volume that conforms to the requirements of Subsection 812.2.04. In addition, obtain approval for use of the material by the Office of Materials and Research.

Apply coatings to the soil reinforcing devices as follows:

123/A 123M. Or galvanize it mechanically according to ASTM B 695, Class 110, unless otherwise specified on the plans. Also galvanize the surfaces created by punching holes for bolts.

fabrication, storage, or erection according to Section 645. Repair by brush coating with an approved galvanizing repair compound as specified in Subsection 870.2.05.A.2 to the Engineer’s satisfaction at no increase in Contract cost.

Hot dip galvanize alignment pins. 1049 1049 1049 1049 1049

Plans with a two-component coal tar epoxy system indicated in Subsection 535.3.03.D, Prepare Steel Piling, Swaybracing, and Concrete Piling Surfaces for Special Protective Coatings, for a Type 2P coating according to Subsection 870.2.05.A.1.

strips. Repair damage to the coating on connecting devices or reinforcing devices from shipping, storage, or erection to the Engineer’s satisfaction at no additional cost.

reinforcing devices.

tie strips.

reinforcing devices.

erection to the Engineer’s satisfaction at no additional cost.

Use reinforcing steel that conforms to the requirements of Section 511.

Use welded wire fabric that conforms to the requirements of ASTM A 82.

The Department will use certified test report as specified in Subsection 106.05, Materials Certification and perform routine tests as a basis for material acceptance furnished for the work.

For the corrosion inhibiting material, use a bituminous plastic cement material that conforms to the requirements of Section 848, AASHTO M 243 Trowel Grade Asphalt Mastic, or use an approved corrosion-inhibiting grease. 626.2.01 Delivery, Storage, and Handling Handle, store, and ship panels to eliminate the danger of chipping, cracking, discoloring, fracturing, and excessive bending stresses. Repair at the plant the panels damaged during handling or storage at the casting plant as directed by the Engineer. Panels damaged during handling, storing, or shipping may be rejected upon delivery at the Engineer’s discretion. Support panels in storage on firm blocking located immediately adjacent to embedded connecting devices to avoid bending the connecting devices. Repair the coating on ties or soil-reinforcing devices damaged during handling or placing to the Engineer’s satisfaction.

626.3Construction Requirements

626.3.01 Personnel

Ensure that the wall crew supervisor has previous satisfactory experience in erecting mechanically stabilized walls. 1050 1050 1050 1050 1050

626.3.02 Equipment General Provisions 101 through 150. 626.3.03 Preparation

Before beginning construction, prepare the foundation as follows:

exceeding the width of the reinforced volume and leveling pad.

Use the top of the leveling pad as the grade elevation.

maximum laboratory dry density as determined by GDT 7.

the lateral limits of the bridge have foundation material compacted to at least 100 percent of maximum

laboratory dry density as determined by GDT 7.

least 100 percent of maximum laboratory dry density as determined by GDT 7.

Place and compact the embankment beneath the wall according to Section 208.

the Office of Materials and Research.

is greater.

Contractor’s expense.

pads of that wall.

foam strips and cover with filter cloth.

(10 mm) of neoprene strips.

replacing panels.

embankment before constructing the leveling pad and placing backfill for the wall.

For step details on leveling pads, see plans and construction details.

626.3.04 Fabrication

Have steel soil-reinforcing devices shop fabricated. Use shop fabricated steel mesh of cold drawn steel welded

into the finished mesh fabric according to ASTM A 185.

Cut soil-reinforcing devices to lengths and tolerances shown on the Plans. Punch holes for bolts in the location

shown. Ensure that soil-reinforcing devices are true to size and free of defects that may impair the strength

or durability. 10511051105110511051

Use connecting devices of the dimensions shown on the Plans. Assemble connecting members and soil-

reinforcing devices before galvanizing the connecting devices. Ensure that the connecting devices are true to size

and are free of defects that may impair the strength or durability.

Tie strips may be partially bent to no more than a 1 in. (25 mm) radius before they are shipped to the precast yard.

Perform final bending at the precast yard.

Do not allow connecting devices, reinforcing steel, or welded wire fabric used in the panels to contact each other.

Ensure that the nominal diameter is as defined in Subsection 626.2.B, Connecting Devices.

Use precast panel materials as specified in Subsection 626.2, Materials. Before casting, set the following in place

to the dimensions and tolerances shown on the drawings:

• Tie strips

• Mesh attachment straps

• Coil embeds

• Coil bolts

• Reinforcing steel

• Welded wire fabric

• Connecting pins

• Handling devices

Do not allow the metal connecting devices and reinforcing steel to contact each other when in their final position

in the panel.

Use precast concrete panels that are cast at a Class A or B plant that conforms to Standard Operating

Procedure 3, Precast/Prestressed Concrete Bridge Members. See QPL 9 for a list of approved plants.

Cast the panels using steel forms.

or architectural form liner. Float finish the back face.

Supplement vibration with hand tamping as necessary to force the concrete into the corners of the forms

and prevent the formation of stone pockets or cleavage planes from forming.

Cure the panels as specified in Subsection 500.3.05.Z, Cure Concrete, or Subsection 865.2.01.B.10, Concrete

Curing. Cure for at least 12 hours or until the concrete develops the specified compressive strength. The

Engineer will reject panels that do not reach specified strength within 28 days.

Keep forms in place until they can be removed without damaging the panel. 10521052105210521052

Finish the concrete surface for the front face as designated on the Plans. Float-finish the rear face enough to

eliminate open aggregate pockets and distortions greater than 1/4 in. (6 mm).

Only use panels manufactured within the following tolerances:

• All dimensions are within 3/16 in. (5 mm).

• Angular distortion in the panel’s height does not exceed 3/16 in. (5 mm) in 5 ft. (1.5 m).

• Diagonal tolerance from Plan dimensions is no more than 3/8 in. (10 mm).

For textured finishes, surface defects greater than 5/16 in. (8 mm) in 5 ft (1.5 m) will be rejected.

Perform compression tests to determine the minimum strength requirements on cylinders.

production and cure according to GDT 35.D.B.6.

Make two additional cylinders from each day’s production or from each 10 cubic yards of concrete

placed, whichever is the lesser amount of concrete, to determine the 28-day strength.

each 10 yd³ (7.5 m³) of concrete placed, whichever amount of concrete is less.

MPa). Perform compressive strength tests according to AASHTO T 22.

Panels will be rejected if they do not meet the requirements above. The following defects are also cause

for rejection:

• Indications of imperfect molding that result in tolerances being exceeded

• Honeycombed or open texture concrete

Clearly and permanently mark on the rear face of each panel the date of manufacture, lot number, and type

of panel.

To construct the precast portion of the coping or precast traffic barrier, use materials that conform to

Subsection 626.2.C, Concrete. Use the same procedures for pre-casting, testing, and inspection as those for

pre-cast panels.

626.3.05 Construction

Place precast panels so that their final position at the completion of the wall is vertical.

movement.

during backfill placement and compaction.

temporary wooden wedges in the joints at the junction of two adjacent panels on the external side of

the wall.

then remove the bottom layer of wedges.

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leveling pads.

is 7/8 in. ± 3/8 in. (22 mm ± 10 mm).

constructed does not exceed 3/4 in. (20 mm) when measured along a 10 ft. (3 m) straightedge.

does not exceed 1/2 in. per 10 ft. (13 mm per 3 m) of wall height.

wall to proper grade. See the plans or construction details.

Before placing special backfill material on a soil-reinforcing device, complete the connections to

the panels.

Treat joints between the panels as follows:

• Use a woven plastic filter fabric sheet to cover the joint on the back side of the wall between panels

from 3 ft. (1 m) above the 100-year flood elevation to the bottom of the wall.

• Use a woven or nonwoven plastic filter fabric sheet to cover the joint on the back side of the wall

between panels from 3 ft. (1 m) above the 100-year high-water elevation to the top of the wall.

pads or elastomeric pads as specified on the Plans. Use ribbed bearing pads that are SBR rubber with a

durometer hardness of 80 plus or minus 10 as required in ASTM D 2240.

1992 AASHTO Specifications for Highway Bridges, Section 18, Elastomeric Bearings.

foam strips, or equal as approved by the Engineer in addition to other required joint treatments.

foam strips together, overlap them at least 4 in. (100 mm).

For vertical joints 18 in. (450 mm) wide

For horizontal joints 12 in. (300 mm) wide

Place backfill shortly after erecting each lift panel. Follow these guidelines: 10541054105410541054

the end of the soil-reinforcing devices.

to drain away from the wall before placing and attaching the next layer of reinforcing devices.

by the Engineer.

this lift thickness to obtain the specified density, if required.

determined by GDT 7 or GDT 24a, GDT 24b Method A or B, for full depth of the material.

and panels.

wide adjacent to the backside of the wall.

After compacting the remainder of the layer, compact this 3 ft. (1 m) strip with light mechanical tampers

without causing the panels to move outward.

that area until the lift is re-compacted and obtains a passing compaction test.

undulations until the special backfill material has been placed and compacted above the restrained layer to

the level of the next layer of stabilizing geogrid. Release the uppermost layer of stabilizing geogrid after the

final layer of special backfill is placed and compacted.

Provide precast panels that have the appropriate storm drain openings into panels at the elevation and locations

indicated on drainage profiles.

Place catch basins so that pipes will enter perpendicular (plan view) to the panels or below the leveling pads

as shown on the Plans. Coordinate the catch basin construction and the storm drain placement with the

wall construction.

Furnish, install, operate, and maintain satisfactory dewatering systems to maintain the site in a dry and workable

condition to permit grading, compacting the wall foundation, and erecting and backfilling the wall. Furnish

dewatering system equipment and materials and continue the system as long as necessary.

When catch basins are located behind the wall and the Wall Plans do not indicate a specific construction method,

use the method outlined in the construction details.

When longitudinal pipes are located behind the wall, follow this procedure if specific details are not shown on the

Wall plans:

the precast panel. See the construction details.

investigate relocating the pipe. The Engineer will contact the design office that designed the drainage system

or the office responsible for the pipe and will investigate the pipe relocation. 10551055105510551055

procedure indicated on the construction details.

Use precast concrete or cast-in-place concrete for:

• Drainage structures that are within the special embankment backfill

• Drainage structures that are outside the special embankment backfill but that are within 5 ft. (1.5 m) of

the front face of the wall

626.3.06 Quality Acceptance

General Provisions 101 through 150.

626.3.07 Contractor Warranty and Maintenance

General Provisions 101 through 150.

626.4Measurement

When a mechanically stabilized embankment retaining wall is built to plan dimensions, the plan quantities are the pay

quantities. When the Engineer changes plan dimensions during construction, or when original Plans are in error, the

revised plan quantities are the pay quantities.

Excavation, including removing unstable material and shoring for construction of the mechanically stabilized

embankment retaining wall, will not be measured and paid for separately.

The panels complete in place and accepted are measured for payment by the square foot (meter). The area of

drains through the wall are not deducted.

The reinforcing strips, backfill stabilizing mesh, or backfill stabilizing geogrid is measured for payment by the linear

foot (meter) of strip, mesh or geogrid.

The special embankment backfill used in the mechanically stabilized embankment retaining wall volume is

measured for payment by the cubic yard (meter) and as shown on the Plans. The limits of the mechanically

stabilized embankment retaining wall volume are as follows:

changes, the volume width change will occur midway between reinforcing device layers.

(1 m) above the uppermost reinforcing device layer. The uppermost reinforcing device layer may be attached

to the wall, traffic barrier, or bridge cap.

embankment retaining wall volume is incidental and is included in the price bid for Contract items. 10561056105610561056

Engineer and requires special embankment backfill to provide stability, as determined by the Engineer,

this will be measured and paid for at the Contract Unit Price bid per cubic yard (meter) for special

embankment backfill.

If undercuts are not provided for on the Plans and the Engineer determines that special embankment backfill

is not appropriate, backfill with foundation material conforming to Subsection 812.2.02, “Foundation Backfill,

Type II. Payment for foundation backfill material used in this application is at the Contract Price bid per cubic

yard (meter) for special embankment backfill.

Backfill for undercut areas that do not require materials of grades higher than common excavation soils will

not be measured or paid for separately.

Concrete leveling pads are measured for payment by the linear foot (meter). This includes steps shown on

the plans.

No separate measurement or payment will be made for dewatering. Include the cost of dewatering in the price bid

for special embankment backfill.

Units on the mechanically stabilized embankment retaining wall, complete in place and accepted, will be

designated on the plans and paid for at the Contract Unit Price bid per linear foot (meter) for each of the following

unit types:

• Cast-in-place coping A

• Cast-in-place coping B

• Precast coping

• Traffic barrier V

• Traffic barrier H

Use traffic barrier H and cast-in-place coping B whenever noise walls, light standards, or other appurtenances are

mounted on top of the barrier or coping. Use traffic barrier V and cast-in-place coping A when no appurtenance is

used on top of the barrier or coping. Cast all traffic barriers in place except traffic barrier H, which is precast when

detailed as precast on the plans.

626.4.01 Limits

General Provisions 101 through 150.

626.5Payment

When mechanically stabilized embankment retaining walls are built to plan dimensions, the plan quantity will be the

pay quantity. When plan dimensions are revised at the Engineer’s direction, mechanically stabilized embankment

retaining wall will be paid for using the revised plan quantities. Payment is full compensation for fabricating,

transporting, and erecting material according to the plans and specifications.

Separate measurement or payment is not made for tools, superintendence, labor, fasteners, coatings, joint materials

(including but not limited to SBR or elastomeric pads, polyether foam, and filter fabric), site preparation, filler concrete,

or other incidentals for performing the work. Soil-reinforcing devices attached to the traffic barrier or coping are not

measured separately for payment but are included in the price bid for traffic barrier or coping.

Concrete side barrier, noise walls, light standards, V-gutters, guard rail, fencing, and handrail, when shown on the

plans, will be paid for according to the applicable sections of the project specifications. Anchor bolts for sleeves for

mounting fencing and light standards or noise walls on the wall are included in the price bid for wall items. 10571057105710571057

Payment will be made under:

Item No. 626 Concrete facia panels Per square foot (meter)

Item No. 626 Backfill stabilizing devices Per linear foot (meter)

Item No. 626 MSE wall backfill material Per cubic yard (meter)

Item No. 626 Concrete leveling pad Per linear foot (meter)

Item No. 626 Cast-in-place coping A Per linear foot (meter)

Item No. 626 Cast-in-place coping B Per linear foot (meter)

Item No. 626 Traffic barrier V Per linear foot (meter)

Item No. 626 Traffic barrier H Per linear foot (meter)

Item No. 626 Precast coping Per linear foot (meter)

626.5.01 Adjustments

General Provisions 101 through 150.. 1058 1058 1058 1058 1058