R 3-01-05

MECHANICALLY STABILIZED EARTH RETAINING WALLS

The Standard Specifications are revised as follows:

SECTION 731, BEGIN LINE 1, INSERT AS FOLLOWS:

SECTION 731 - MECHANICALLY STABILIZED EARTH RETAINING WALLS

731.01 Description. This work shall consist of furnishing materials and

placement of mechanically stabilized earth retaining walls in accordance 105.03.
10
The Contractor shall perform the necessary work to verify that the foundation is
at the correct elevation, that the wall is constructed to the correct alignment, and that
the work is in accordance with the specified tolerances. The checking of alignments and
tolerances shall include verifying that the plumbness of the face panels is in accordance
with 731.10 over the entire height of the wall. Alignment shall be checked at each layer
of panels after the backfill behind the panels has been compacted, and the results shall
be recorded.

731.02 General Design Requirements. The mechanically stabilized earth wall

20 shall consist of a non-structural leveling pad, concrete face panels, coping, and ground
reinforcement elements mechanically connected to each panel. Ground reinforcement
shall have sufficient strength, frictional resistance, and quantity as required by design.

The mechanically stabilized earth retaining walls system is to be selected from

the Department's list of approved Retaining Wall Systems. A Retaining Wall System
manufacturer may be included on the Department’s list by following procedure J of
ITM 806. The quantities shown in the Schedule of Pay Items will be the same for all
mechanically stabilized earth wall systems. All mechanically stabilized earth walls shall
be constructed in accordance with the approved plans and panel shop drawings based on
30 the requirements herein. The recommendations of the wall system suppliers shall not
override the minimum performance requirements contained herein.

If the wall manufacturer needs additional information to complete the design,

the Contractor shall be responsible for obtaining such information.

All appurtenances behind, in front of, under, mounted upon, or passing through
the wall such as drainage structures, utilities, or other appurtenances shown on the
plans shall be accounted for in the stability design of the wall.

40 The mechanically stabilized earth wall design shall follow the general
dimensions of the wall envelope shown on the plans. The plans will locate the leveling
pad at or below the theoretical leveling pad. The top of the face panel shall be at or
above the top of the panel elevation shown on the plans.

Where coping or barrier is utilized, the wall face panel shall extend up into the
coping or barrier a minimum of 50 mm (2 in.). The top of the face panels may be level
or sloped to meet the top of the face panel line noted. Cast-in-place concrete will not be
an acceptable replacement for panel areas noted by the wall envelope.

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50 Where walls or wall sections intersect with an included angle of 130 degrees or
less, a vertical corner element separate from the standard panel face shall abut and
interact with the opposing standard panels. The corner element shall have ground
reinforcement connected specifically to that panel and shall be designed to preclude
lateral spread of the intersecting panels.

Face panels shall be designed to accommodate differential settlement of 1 linear

unit in 100. Face panels of greater than 3.0 m2 (32 sq ft) up through 6.0 m2 (64 sq ft) in
area shall be designed to accommodate differential settlement of 1 linear unit in 200.
Where shown on the plans, slip joints to accommodate excessive or differential
60 settlement shall be included.

A project that is part of a contract with multiple projects or contracts containing

MSE walls shall only use rectangular face panels.

731.03 Design Criteria. The design by the manufacturer shall consider the
internal and the external stability of the wall mass including the applied bearing
pressure, overturning, sliding, and stability of temporary construction slopes. The
design shall be in accordance with the design, construction, and commentary divisions
of the AASHTO Standard Specifications for Highway Bridges, unless specified
70 otherwise herein. The analysis of settlement, bearing capacity, and overall slope
stability will be the responsibility of the Engineer.

The theoretical failure plane within the soil mass shall be analyzed so that the
soil stabilizing component extends sufficiently beyond the failure plane to stabilize the
material. External loads which affect the internal stability such as those applied through
piling, bridge footings, traffic, and slope surcharge, shall be accounted for in the
design. The size of all structural elements shall be determined such that the design load
stresses do not exceed the allowable stresses found in the AASHTO Standard
Specifications for Highway Bridges, unless otherwise shown on the plans.
80
The maximum allowable yield stress for reinforcement shall be 450 MPa
(65,000 psi).

The phi (φ) angle for the internal design of the volume shall be assumed to be
34 degrees. The φ angle of the backfill behind the mechanically stabilized earth mass
shall be assumed to be 30 degrees.

The wall shall be defined by the wall envelope as shown on the plans. For
design purposes, the height of wall H shall be measured from the theoretical top of the
90 leveling pad to the top of the wall. For a level surcharge situation, the top of the wall
shall be measured to the top of the coping or to the gutter line of the traffic barrier. The
top of the wall shall be the theoretical top of the face panels only when a coping or
barrier is not used. For an abutment face, the design height H shall be defined as the
height measured from the top of the leveling pad to the top of the roadway surface. For
a wall with a sloping surcharge the top of the wall shall be measured at a point 0.3H
back from the face where the design height is H and the actual wall height is H.

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For aesthetic considerations and to make differential settlement unnoticeable, the

panels shall be erected such that the horizontal site line is discontinuous at every other
100 panel. This shall be accomplished by starting erection with the lower panel level of
each wall by alternating full height and half height panels. Panels above the lowest level
shall be of a standard size except as required to top out the wall to be in accordance
with the plan elevations.

The connections of the ground reinforcing steel to the panels shall be in two
elevations for standard panels. The connections shall not be more than 750 mm (30 in.)
apart vertically. To prevent out-of-plane rotation, standard face panels shall be
connected to ground reinforcement on at least three different points in two different
planes. However, preapproved systems utilizing a horizontal stabilizing leg to prevent
110 rotation shall only require ground reinforcement attachments in one plane. Partial
panels shall have three different connection points, but only one plane shall be attached
to ground reinforcement. Panels, which are located at the top of the wall, shall not be
attached to the coping or the traffic barrier.

The ground reinforcement shall be the same length from the bottom to the top of
each wall section whether bar mats, grids, or strips steel are used. Differing ground
reinforcement elements shall be clearly marked for ease of construction. This element
may be used individually or in a prefabricated grouping. The minimum length of the
ground reinforcement shall be 2.5 m (8 ft) or 0.7H in accordance with the AASHTO
120 Standard Specifications for Highway Bridges for an abutment on a spread footing.

The ground reinforcement for the mechanically stabilized earth volume shall be
sized using the lesser of the allowable forces for each specific connection and each
specific reinforcing element. The connection's allowable force shall be taken as 2/3 of
the connection test load at the allowable pullout deformation limit of 13 mm (1/2 in.) or
one half of the ultimate load, whichever is less.

The ground reinforcement length shall be as required for internal design or as

shown on the plans. The length shall exceed the minimum noted as required for design
130 consideration. One hundred percent of the ground reinforcement, which is designed and
placed in the reinforced earth volume shall extend to and shall be connected to the face
panels.

For mats, grids, or strip steel, the minimum zinc coating thickness shall be 610
g/m2 (2 oz/sq ft). Such thickness shall be assumed to be 86:m for purpose of
calculation of reduced structural section.

The actual applied bearing pressures under the stabilized mass for each
reinforcement length shall be clearly indicated on the shop drawings and shall be equal
140 to or less than the maximum allowable soil pressure shown on the plans. Passive
pressure in front of the wall mass will be assumed to be zero for design purposes.

731.04 Submittals. The Contractor shall submit one copy of the design
computations for approval. If the computations are computer generated, one sample set
of hand calculations, for one wall location, shall also be submitted. The Contractor
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shall submit eight sets of design drawings for approval after the design computations
are approved and before beginning wall construction operations. Design computations
and design drawings shall be signed and sealed by a professional engineer.

150 (a) The design drawings shall include all details, dimensions, quantities and
cross-sections necessary to construct the wall and shall include but shall
not be limited to the following:

1. A plan and elevation sheet or sheets for each wall

2. An elevation view of the wall which shall include the elevation at the
top of the wall at all horizontal and vertical break points at least
every 15 m (50 ft) along the face of the wall, all steps in the leveling
pads, the designation as to the type of panel, the length of soil
160 reinforcing systems, the distance along the face of the wall to where
changes in length of the soil reinforcing systems occur, and an
indication of the original and final ground lines and maximum
bearing pressures

3. A plan view of the wall that indicates the offsets from the
construction centerline to the face of the wall at all changes in
horizontal alignment. A plan view and elevation view which detail
the placing position and connection of all steel ground reinforcing
elements in areas where piling, utility, or other structures are near
170 the wall.

4. A typical cross section or cross sections showing elevation

relationship between ground conditions and proposed grades

5. All general notes required for constructing the wall

6. All horizontal and vertical curve data affecting the wall

7. A listing of the summary of quantities on the elevation sheet for each

180 wall

(b) All panel details shall show all dimensions necessary to construct the
element, all reinforcing steel in the element, and the location of soil
reinforcing system devices embedded in the panels.

(c) The details for construction of walls around drainage facilities and the
out-letting of internal drainage from the backfill volume.

(d) All details of the architectural treatment.

190
(e) The details for diverting strips or mesh around obstructions such as piles,
catch basins, and other utilities shall be submitted for approval.

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(f) The details for each connection between the concrete panel and the mesh
or strip.

(g) Calculations for the φ angle of the internal design and backfill.

Design calculations and shop drawings shall be submitted to the Engineer for
200 review and approval.

MATERIALS

731.05 Materials. The Contractor shall make arrangements to purchase the

materials described herein, including concrete face panels, retaining strips or mesh, tie
strips, fasteners, joint materials, and all necessary incidentals, from a mechanically
stabilized earth wall system manufacturer on the Departments list of approved Retaining
Wall Systems.

210 Materials shall be in accordance with the following:

B Borrow ... .......................................................211.02

Coarse Aggregate, Class A or Higher, Size No. 8 or 91 ...904
Concrete Admixtures ..............................................912.03
Concrete, Class A..................................................702
Fine Aggregate, Size No. 23.....................................904
Fly Ash ..............................................................901.02
Geotextile............................................................913.18
Portland Cement....................................................901.01(b)
220 Rapid Set Patching Materials ....................................901.07
Reinforcing Steel ...................................................910.01
Structure Backfill * ............................................... 904
Water .................................................................913.01

* No slags other than ACBF will be permitted. ACBF shall be Class A or Higher, Size No. 8 in
accordance with 904.

Backfill material used in the mechanically stabilized earth wall volume shall be
structure backfill.
230
The internal friction or φ angle of the structure backfill in the reinforced soil
mass shall be not less than 34 deg in accordance with AASHTO T 236 or AASHTO T
297 under consolidated drained conditions. Testing for the φ angle and permeability
shall be performed on the portion finer than 2.36 mm (No. 8) sieve, using a sample of
the material compacted to 95% in accordance with AASHTO T 99, methods C, or D.
No testing for the φ angle is required when 80% of the materials are greater than 4.75
mm (No. 4) sieve. An approved geotechnical laboratory shall perform the tests.

Structure backfill criteria shall be as follows:

240
Property Criteria Test Method
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pH 5 < pH < 10 AASHTO T 289

Chlorides < 100 ppm AASHTO T 291
Sulfates < 200 ppm AASHTO T 290
Organic Content 1 % max. AASHTO T 267
Resistively 3000 Ω - cm (min.) AASHTO T 288
Permeability 30 m/day AASHTO T 215
(100 ft/day) (min.)
*Permeability may be reduced to 10 m/day (30 ft/day) when any portion of the pavement structure is not
directely above the MSE wall ground reinforcement envelope.

If the minimum resistivity exceeds 5000 Ω - cm, the requirement of the testing
for Chlorides and Sulfates may be waived. The resistivity shall be tested at 100%
saturation.

ACBF shall be in accordance with the pH, Chlorides, Sulfates, Organic

Content, Resistivity and Permeability requirements of structural backfill as noted above
250 and ITM 212. Total sulfides shall also be determined in accordance with EPA 376.1,
using the 100 mL pH water samples obtained during ITM 212, and shall not exceed 400
ppm. The ACBF shall have a maximum corrosion rate as follows for steel and zinc
when tested in accordance with ASTM G 59.

1. Zinc Corrosion Rate First 2 years.................................. 15 µm/yr./side

2. Zinc corrosion to depletion............................................ 4 µm/yr./side
3. Carbon steel rate ...................................................... 12 µm/yr./side

If ACBF or coarse aggregate No. 8's are used, and soil, B borrow, structural
260 backfill, or coarse aggregate No. 53's are to be placed above the ACBF or No. 8
aggregate, a single layer of geotextile shall be placed on top of the ACBF aggregate in
accordance with 616.10. A type C certification in accordance with 916 for the
geotextile materials shall be furnished to the Engineer prior to use.

The structure backfill shall be supplied in accordance with 904 and a type A
certification in accordance with 916 for the above additional testing of the structure
backfill shall be furnished to the Engineer prior to use. One copy of all test results
performed by the Contractor, which are necessary to demonstrate compliance with the
specifications, shall also be furnished to the Department's Geotechnical Section. An
270 approved geotechnical laboratory shall perform the tests.

(a) Concrete Face Panels. Concrete shall be in accordance with the

applicable requirements of 702. Concrete shall have a compressive strength equal to or
greater than 27.5 MPa (4000 psi) at 28 days.

Retarding agents, accelerating agents, or additives containing chloride shall not

be used without approval. Air-entraining and slump requirements shall be in accordance
with 702.05.

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280 Ground reinforcement connecting hardware and rebar lifting devices shall be set
in place and secured prior to beginning casting, in accordance with the dimensions and
tolerances shown on the design drawings.

1. Testing and Inspection. Acceptability of the panels will be determined

on the basis of compressive strength tests and visual inspection. The panels shall be
considered acceptable regardless of curing age when compressive test results indicate
that the compressive strength is in accordance with 731.05(a). The wall manufacturer of
the panels shall provide for all testing and inspection services during the production of
the panels. Services shall be completed by a Department approved testing laboratory.
290 An American Concrete Institute certified concrete field testing technician, grade 1, shall
be present during production of the face panels to direct all sampling and testing.

2. Casting. The panels shall be cast on a flat area, with the front face of
the form at the bottom, and the back face at the upper part. Tie strip guides shall be set
on the rear face. The concrete in each unit shall be placed without interruption and shall
be consolidated as necessary to prevent the formation of segregation or cleavage planes.
Clear form oil of one manufacture shall be used throughout the casting operation.

3. Curing. The panels shall be cured for a sufficient length of time such
300 that the concrete develops the specified compressive strength.

4. Removal of Forms. The forms shall remain in place until they may be
removed without damage to the unit.

5. Concrete Finish. The concrete surface for the front panel face shall
have a surface finish produced from contact with the form. The rear face of the panel
shall be roughly screeded to eliminate open pockets of aggregate and surface distortions
in excess of 6 mm (1/4 in.).

310 6. Tolerances. All panels shall be manufactured within the tolerances as

follows:

a. Panel Dimensions. Lateral position of tie strips shall be within 25

mm (1 in.). All other dimensions shall be within 5 mm (3/16 in.).

b. Panel Squareness. Squareness, as determined by the difference

between the two diagonals, shall not exceed 13 mm (1/2 in.).

c. Panel Surface Finish. Surface defects on smooth formed surfaces

320 measured on a length of 1.5 m (5 ft) shall not exceed 3 mm (1/8 in.). Surface defects
on textured finished surfaces measured on a length of 1.5 m (5 ft) shall not exceed 5
mm (5/16 in.).

7. Compressive Strength. Acceptance of the concrete panels with respect

to compressive strength will be determined on the basis of production lots. A
production lot is defined as 50 panels.

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Frequency of production control testing will consist of a minimum of one test

per production lot but not less than one test per day. The wall manufacturer will sample
the concrete in accordance with AASHTO T 141 and prepare a minimum of two
330 cylinders in accordance with AASHTO T 23. Curing of the cylinders shall be in the
same manner as the panels are cured.

When the average results of two cylinders tested in accordance with AASHTO
T 22, meet or exceeds the requirements of 731.05(a), the production lot panels or those
panels represented by a day's testing may be shipped.

When the cylinder test results are less than the requirements of 731.05(a) and
additional cylinders for testing are not available, the manufacturer may core the panels.
The wall manufacture will randomly select two panels from the lot for core testing in
340 accordance with AASHTO T 24. The wall manufacture shall obtain one core on the
backside of each panel with a device that produces uniform test samples without coring
completely through the panel. Coring shall not be located within 150 mm (6 in.) of the
panel fasteners or the edges of the panels and shall avoid the panel's reinforcing steel.
The wall manufacture shall fill the core holes with equivalent concrete materials or
rapid set patching materials and trowel to produce a smooth finish. Excess material
removed during troweling shall not be reused. If rapid set patching material is used,
mixing and curing shall be in accordance with the manufacture's recommendations. If
the average strength test results from the cores meet or exceed the requirements of
731.05(a), the production lot panels may be shipped.
350
A type A certification in accordance with 916 shall be furnished for each
shipment prior to use of the panels. All cylinder or core test results, including the age
of the cylinders or cores at the time of testing, shall be included on the certification for
each production lot.

Verification of compressive strengths of the panels will be conducted by the

Engineer. The frequency of verification testing will be one test for every 750 panels per
manufacturer with a minimum of one test per contract. One panel will be randomly
selected and two locations selected for coring. The Engineer will obtain two 100 mm (4
360 in.) cores on the backside of the panel without coring completely through the panel.
The Contractor shall refill the core holes with rapid set patching materials and trowel to
produce a smooth finish. Excess material removed during troweling shall not be reused.
Mixing and curing of the patching materials shall be in accordance with the
manufacture's recommendations.

The Engineer will test the cores in accordance with AASHTO T 24. The
verification test results will be averaged and compared to the manufacturer’s results
reported on the certification. If the initial verification test results do not meet the
requirements of 731.05(a), the Engineer will randomly select two different panels for
370 additional verification testing. If the additional verification tests meet the requirements
of 731.05(a), no further action is required. If the test results still do not meet the
requirements of 731.05(a), installation of panels shall cease and the Engineer will
conduct an investigation. Panels manufactured on the same dates as the panels cored for
verification tests that have already been installed will be considered and adjudicated as a
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failed material in accordance with normal Department practice as listed in 105.03. The
Engineer will conduct verification testing until three consecutive dates of production
meet the strength requirements of 731.05(a). The Contractor or wall manufacturer shall
make arrangements so that panels from three consecutive dates of production are
accessible for coring. Installation of panels may resume once acceptable verification
380 testing results are achieved.

8. Rejection. Units shall be subject to rejection due to failure to be in

accordance with the requirements specified above. In addition, the following defects
may be sufficient cause for rejection:

a. Defects which indicate imperfect molding

b. Defects which indicate honeycombed or open texture concrete

390 c. Defects in the physical characteristics of the concrete, such as

broken or chipped concrete, or color variations or dunnage marks
on the front face due to excessive form oil or other reasons.

The Engineer will determine whether spalled, honeycombed, chipped, or

otherwise defective concrete shall be repaired or be cause for rejection. Repair of
concrete, if permitted, shall be completed in a satisfactory manner. Repair to concrete
surfaces that are to be exposed to view after completion of construction shall be subject
to approval.

400 9. Marking. The place and date of manufacture, and production lot
number shall be clearly scribed on the rear face of each panel.

10. Handling, Storage, and Shipping. All panels shall be handled,

stored, and shipped so as to eliminate the danger of chipping, cracks, fractures, and
excessive bending stresses. Panels in storage shall be supported on firm blocking
located immediately adjacent to tie strips to avoid bending the tie strips.

(b) Concrete Leveling Pad. Concrete, Class A, for the leveling pad shall be
in accordance with the applicable requirements of 702.
410
(c) Concrete Coping. Concrete, Class A, for the coping shall be in
accordance with the applicable requirements of 702. Reinforcing steel in the coping
shall be in accordance with the applicable requirements of 703. The coping may be
precast or cast-in-place.

(d) Reinforcing Mesh, Clevis Connector, and Connector Bar. The

reinforcing mesh shall be shop fabricated of cold drawn steel wire in accordance with
ASTM A 82 and shall be welded into the finished mesh fabric in accordance with
ASTM A 185. Galvanization shall be in accordance with ASTM A 123.
420
Clevis connectors, if used, shall be attached to the alignment templates using the
bars provided with the forms. The vertical and horizontal alignment of the connectors
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shall be +3 mm (+1/8 in.). The holes inside the loops shall be free of all concrete and
debris, loose or otherwise.

The clevis connector shall be fabricated of cold drawn steel wire in accordance
with ASTM A 82 and welded in accordance with ASTM A 884. Loops shall be
galvanized in accordance with ASTM A 153 Class B-3 or ASTM A 123.

430 The connector bar, if used, shall be fabricated of cold drawn steel wire in
accordance with ASTM A 884 and galvanized in accordance with ASTM A 123.

A type A certification in accordance with 916 for reinforcing mesh, clevis

connector, and connector bars shall be furnished prior to use of the materials.

(e) Ground Reinforcement. The ground reinforcement may be a deformed

steel strip or a welded wire grid. The grid or strip used shall be consistent with that
used in the pullout test and shall be consistent throughout the project.

440 The grid shall consist of not less than two longitudinal wires, perpendicular to
the wall, welded to equally spaced cross ribs capable of developing passive pressure
with the fill. The deformed strip shall be of constant width. The strip thickness shall
vary only from the standard undeformed section to the standard deformed section as
required to produce the pullout resistance.

All longitudinal wires of each welded wire grid shall be of the same diameter.
All transverse wires of each welded wire grid shall be of the same diameter, but not
necessarily the same as the longitudinal wire diameter.

450 The face panel edges shall be configured to conceal the joints. All horizontal
and vertical joints shall be covered with a joint cover to prevent backfill leakage while
passing water.

Reinforcing strips shall be hot rolled from bars to the required shape and
dimensions. Physical and mechanical properties of the strips shall be in accordance with
ASTM A 572M Grade 450 (A 572 Grade 65). Tie strips shall be shop fabricated with
hot rolled steel in accordance with the minimum requirements of ASTM A 709M Grade
345 (A 570 Grade 50). Galvanization for reinforcing strips and tie strips shall be in
accordance with ASTM A 123 and the minimum zinc coating thickness shall be 0.64
460 L/m2 (2 oz/sq ft). All reinforcing strips and tie strips will be inspected to ensure that
they are true to size and free from defects which may impair their strength and
durability.

A type A certification in accordance with 916 shall be furnished for ground

reinforcement prior to use of the materials.

(f) Reinforcing Steel. Mill certificates for reinforcing steel as shown on the
plans shall be furnished for approval. All reinforcing steel shall be in accordance with
ASTM A 709M Grade 400 (A 615 Grade 60).
470
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A type A certification in accordance with 916 shall be furnished for reinforcing

steel prior to use of the materials.

(g) Fasteners. Fasteners shall consist of 13 mm (1/2 in.) diameter, hexagonal

cap screw bolts and nuts, which shall be galvanized and in accordance with ASTM A
325M (A 325).

A type A certification in accordance with 916 shall be furnished for fasteners

prior to use of the materials.
480
(h) Alignment Pins. The rods used to align the face panels during
construction shall be 19 mm (3/4 in.) diameter, 300 mm (12 in.) long. The rods shall
be mild steel, polyvinyl chloride, or fiberglass. A sample shall be submitted prior to
use to the Materials and Tests Division for approval.

(i) Joint Materials. Bearing pads shall be rubber, neoprene, polyvinyl

chloride, or polyethylene, and of the type and grade recommended by the supplier of
the mechanically stabilized earth wall system.

490 The joint cover shall be either a non-woven needle punch polyester geotextile or
a woven monofilament polypropylene. The joint cover shall be attached to the rear face
of the panels with a suitable adhesive.

Horizontal and vertical joints shall be provided between adjacent face panels to
prevent concrete-to-concrete contact and chipping when differential settlement occurs.
The horizontal and vertical joints shall contain compression blocks, pins, or other
approved means as recommended by the manufacturer to provide a uniform joint.
Panels without an uninterrupted vertical joint shall have a minimum joint thickness of
19 mm (3/4 in.).
500
A type A certification in accordance with 916 for joint materials shall be
furnished prior to use of the materials.

CONSTRUCTION REQUIREMENTS

731.06 General Requirements. The wall manufacturer representative shall

provide technical instruction, guidance in pre-construction activities including the
preconstruction conference, and on-site technical assistance to the Contractor during
construction.
510
731.07 Foundation Preparation. The foundation for the structure shall be graded
level for a width equal to or exceeding the length of the reinforcing strips or as shown
on the plans. Prior to wall construction, the foundation, if not in rock, shall be
compacted in accordance with 203. The base of the wall excavation shall be proofrolled
with an approved compacting equipment. If unsuitable foundation material is
encountered, it shall be removed and replaced with B borrow in accordance with
211.02 and compacted in accordance with 211.04.

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At each foundation level, an unreinforced concrete leveling pad shall be

520 provided as shown on the plans. The leveling pad shall be cured in accordance with
702.22 a minimum of 12 h before placement of concrete face panels.

731.08 Retaining Wall Excavation. This work shall consist of the excavation of
material whose removal is necessary for the construction of the mechanically stabilized
earth walls in accordance with the plans, the requirements herein, or as directed.
Excavation shall include the construction and subsequent removal of all necessary
bracing, shoring, sheeting, cribbing, an all pumping, bailing, and draining.

Prior to starting excavation operations at the wall site, clearing and grubbing
530 shall be in accordance with 201.03. The Contractor shall clear and grub the area to the
excavation in accordance with the limits shown on the plans. All timber, stumps, and
debris shall be disposed of in accordance with 201.03.

The Contractor shall notify the Engineer a sufficient time before beginning the
excavation so that measurements may be taken of the undisturbed ground.

Where necessary for safety, the excavation shall be shored or braced in

accordance with State and local safety standards. Excavation and related work shall be
performed such that no portion of the wall is endangered by subsequent operations.
540
Where excavation for the wall is adjacent to a traveled way, the method for
shoring, sheeting, or bracing the excavation opening shall be approved before
beginning the excavation. The Contractor shall submit five copies of drawings in
accordance with 206.09 showing details of the proposed method of excavation
protection.

After the excavation for each wall location has been performed, the Contractor
shall notify the Engineer. Concrete for the leveling pad shall not be placed until the
Engineer has approved the depth of the excavation and the foundation material.
550
All sheeting and bracing shall be removed as the backfilling progresses.

All material for backfill shall be subject to approval and shall be free from large
or frozen lumps, wood, or other undesirable material. All backfill shall be compacted
in accordance with 203.

731.09 Wall Erection. Concrete face panels shall be handled by means of a

lifting device set into the upper edge of the panels. Panels shall be placed in successive
horizontal lifts in the sequence shown on the plans as backfill placement proceeds. As
560 backfill material is placed behind the panels, the panels shall be maintained in vertical
position by means of temporary wooden wedges placed in the joint at the junction of the
two adjacent panels on the external side of the wall. External bracing will be required
for the initial lift.

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Panels placed in contact with the ground or covered by standing water shall have
face discoloration removed by means of a chemical wash. Panels shall be stored on
blocking to minimize contact with the ground or being covered by standing water.

Plumbness, vertical tolerances, and horizontal alignment tolerances shall not

570 exceed 19 mm (3/4 in.) when measured with a 3 m (10 ft) straightedge. The maximum
allowable offset in panel joints shall be 19 mm (3/4 in.). The overall plumbness from
top to bottom of the wall shall not exceed 13 mm per 3 m (1/2 in. per 10 ft) of wall
height.

Ground reinforcing shall be placed normal to the face of the wall, unless
otherwise shown on the plans or as directed. Prior to placement of the ground
reinforcing strips, backfill shall be compacted in accordance with 731.10.

731.10 Backfill Placement. Backfill placement shall closely follow erection of

580 each course of panels and ground reinforcing. Backfill shall be placed so as to avoid
damage or disturbance to the wall materials or misalignment of the concrete face
panels. Wall materials that become damaged or disturbed during backfill placement
shall be removed and replaced or corrected as directed. All misalignment or distortion
of the concrete face panels due to placement of backfill outside the limits described
herein shall be corrected as directed.

The work shall also include B borrow backfilling above a theoretical 1:1 slope
behind the ground reinforcement in accordance with the details shown on the plans.

590 Structure backfill shall be compacted to 95% of the maximum dry density in
accordance with AASHTO T 99. Compaction equipment shall be in accordance with
409.03(d). Density of the compacted aggregate will be determined in accordance with
203.24(b). If No. 8 backfill materials are used, compaction shall consist of four passes
with a vibratory roller, and one pass with the same roller in static mode. A vibratory
roller shall be equipped with a variable amplitude system, a speed control device, and
have a minimum vibration frequency of 1000 vibrations per min. A roller in accordance
with 409.03(d)4 may be used. All displacement or rutting of the aggregate shall be
repaired prior to placing subsequent material.

600 The maximum loose lift thickness shall not exceed 200 mm (8 in.) except that
lifts 1 m (3 ft) from the wall or closer shall not exceed 125 mm (5 in.) in loose
thickness. This lift thickness shall be decreased if necessary, to obtain the specified
density.

Compaction within 1 m (3 ft) of the back face of the concrete face panels shall
be achieved by means of a minimum of five passes with a lightweight mechanical
tamper, roller, or an alternative vibratory system.

At the end of each day's operation, the last level of backfill shall be sloped away
610 from the concrete face panels. In addition, surface runoff from adjacent areas shall not
be permitted to enter the wall construction site.

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Cutting or altering of the basic structural section of ground reinforcing at the

site will be prohibited, unless the cutting is preplanned and detailed on the approved
design drawings. Cutting shall only be considered if adequate additional ground
reinforcing is provided to produce the required strength shown in the approved
calculations. If the grid or strip is shortened in the field, the cut ends shall be covered
with a galvanized paint or Bitumastic 50 coal tar to prevent corrosion of the metal.

620 731.11 Method of Measurement. Concrete face panels and wall erection will be
measured by the square meter (square foot) of wall surface area. The concrete leveling
pad will be measured by the meter (linear foot). Structure backfill and B borrow will be
measured in accordance with 211.09. Unsuitable foundation materials, if found, will be
measured in accordance with 211.09. Geotextile materials if used in accordance with
731.05 will not be measured.

The measurement of concrete face panels, and wall erection will be based on the
neat line limits of the wall envelope as shown on the plans and not that of the wall
system supplier. The wall envelope limits will be considered to be the vertical distance
630 from the top of the leveling pad to the top of the coping, and the horizontal distance
from the beginning to the end of the leveling pad.

Precast or cast-in-place concrete coping will not be measured. Drainage of the

backfill including piping, aggregates and geotextile materials will not be measured.

731.12 Stockpiled Concrete Face Panels. Partial payment will be made for
panels stockpiled on the project site or at the Contractor's approved storage location.
Partial payment will be based on the delivered cost of the wall panels, as verified by
invoices that include freight charges. The Contractor shall furnish the invoices and
640 Type A certification. The partial payment will not exceed 75% of the contract unit
price for concrete face panels. Prior to construction, the Engineer will verify that the
panels are in accordance with 731.05(a).

731.13 Basis of Payment. Concrete face panels and wall erection will be paid
for at the contract unit price per square meter (square foot). The concrete leveling pad,
complete and in place, will be paid for at the contract unit price per meter (linear foot)
for leveling pad. Structure backfill and B borrow will be paid for at the contract unit
price per cubic meter (cubic yard) in accordance with 211.10. Unsuitable foundation
materials will be paid for in accordance with 211.10.
650
Payment will be made under:

Pay Item Metric Pay Unit Symbol (English Pay Unit Symbol)

Face Panels, Concrete....................................................... m2 (SFT)

Leveling Pad, Concrete .......................................................m (LFT)
Wall Erection ................................................................. m2 (SFT)

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The cost of services including the testing laboratory, certified testing personnel,
660 and the testing and inspection of the concrete panels shall be included in the cost of
concrete face panels.

The cost of all mechanically stabilized earth wall materials including concrete
face panels, ground reinforcing, tie strips, fasteners, joint materials, concrete coping,
repair or replacement of face panels damaged or removed due to backfill placement,
and incidentals shall be included in the cost of concrete face panels.

The cost of all labor and materials required to prepare the wall foundation, place
the ground reinforcing, and erect the concrete face panels shall be included in the cost
670 of wall erection.

The cost of labor and materials required to provide for the drainage of the
backfill including piping, aggregates, and geotextile materials shall be included in the
cost of concrete face panels.

The cost of refilling and refinishing of the core holes from verification coring
shall be included in the cost of concrete face panels.

The cost of performing the laboratory tests by an approved geotechnical

680 laboratory for structural backfill or ACBF slag shall be included in the cost of the pay
items in this section.

The cost of all excavation required shall be included in the costs of the pay
items in this section.

The cost of all labor and materials for geotextile materials, used, shall be
included in the cost of the pay items in this section.

The cost of cutting, altering, and recoating of the ground reinforcing at the site
690 shall be included in the cost of wall erection.

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