SPECIFICATION
FOR SEGMENTAL RETAINING WALL SYSTEMS
PART 1: GENERAL
1.01 Description
A. Work includes furnishing and installing segmental
retaining wall (SRW) units to the lines and grades designated on the construction drawings
or as directed by the Architect/Engineer.
Also included is furnishing and installing appurtenant
materials required for construction of the retaining wall as shown on the construction
drawings.
1.02 Reference Standards
A. Segmental Retaining Wall Units
1. ASTM C 140 - Sampling and Testing Concrete Masonry Units
B. Geosynthetic Reinforcement
1. ASTM D 4595 - Tensile Properties of Geotextiles by the
Wide-Width Strip Method.
2. ASTM D 5262 - Test Method for Evaluating the Unconfined
Creep Behavior of Geosynthetics
3. GRI:GG1 - Single Rib Geogrid Tensile Strength
4. GRI:GG5 - Geogrid Pullout
C. Soils
1. ASTM D 698 - Moisture Density Relationship for Soils,
Standard Method
2. ASTM D 422 - Gradation of Soils
3. ASTM 4318 - Atterberg Limits of Soil
D. Drainage Pipe
1. ASTM 3034 - Specification for Polyvinyl Chloride (PVC)
Plastic Pipe
2. ASTM D1248 - Specification for Corrugated Plastic Pipe
E. Where specifications and reference documents conflict,
the Architect/Engineer shall make the final determination of applicable document.
1.03 Submittals
A. Material Submittals: The Contractor shall submit
manufacturers' certifications two weeks prior to start of work stating that the SRW units
and geosynthetic reinforcement meet the requirements of Section 2 of this specification.
B. Design Submittal: The Contractor shall submit two sets
of detailed design calculations and construction drawings for approval at least two weeks
prior to the beginning of wall construction. All calculations and drawings shall be
prepared and sealed by a professional Civil Engineer (Wall Design Engineer) experienced in
SRW wall design and licensed in the state where the wall is to be built.
1.04 Delivery, Storage and Handling
A Contractor shall check materials upon delivery to assure
that specified type and grade of materials have been received and proper color and texture
of SRW units have been received.
B. Contractor shall prevent excessive mud, wet concrete,
epoxies, and like materials which may affix themselves, from coming in contact with
materials.
C. Contractor shall store and handle materials in
accordance with manufacturer's recommendations.
D. Contractor shall protect materials from damage. Damaged
materials shall not be incorporated into the retaining wall.
PART 2: MATERIALS
2.01 Segmental Retaining Wall Units
A. SRW units shall be machine formed, Portland Cement
concrete blocks specifically designed for retaining wall applications. SRW units currently
approved for this project are:
Versa-Lok Retaining Wall Units as manufactured by
___________________.
B. Color of SRW units shall be _____________.
C. Finish of SRW units shall be split face.
D. SRW unit faces shall be of straight geometry.
E. SRW unit height shall be six inches.
F. SRW units (not including aggregate fill in unit voids)
shall provide a minimum weight of 105 psf wall face area.
G. SRW units shall be solid through the full depth of the
unit.
H. SRW units shall have a depth (front face to rear) to
height ratio of 2:1, minimum.
I. SRW units shall be interlocked with connection pins,
designed with proper setback to provide 8:1 vertical to horizontal batter (a 7 degree cant
from vertical).
J. SRW units shall be capable of being erected with the
horizontal gap between adjacent units not exceeding 1/8 inches.
K. For any corners shown on the construction plans, SRW
units shall be capable of providing overlap of units on each successive course so that
walls meeting at corner are interlocked and continuous. SRW units that require corners to
be mitered shall not be allowed.
L. SRW units shall be capable of providing a split face,
textured surface for all vertical surfaces that will be exposed after completion of wall,
including any exposed sides and backs of units.
M. SRW units shall be sound and free of cracks or other
defects that would interfere with the proper placing of the unit or significantly impair
the strength or permanence of the structure. Cracking or excessive chipping may be grounds
for rejection. Units showing cracks longer than 1/2" shall not be used within the
wall. Units showing chips visible at a distance of 30 feet from the wall shall not be used
within the wall.
N. Concrete used to manufacture SRW units shall have a
minimum 28 days compressive strength of 3,000 psi and a maximum moisture absorption rate,
by weight, of 8% as determined in accordance with ASTM C 140. Compressive strength test
specimens shall conform to the saw-cut coupon provisions of Section 5.2.4 of ASTM C140
with the following exception: Coupon shall be taken from the least dimension of the unit
of a size and shape representing the geometry of the unit as a whole.
O. SRW units' molded dimensions shall not differ more than
+ 1/8 inch from that specified, except height which shall be + 1/16 inch as measured in
accordance with ASTM C140.
2.02 Segmental Retaining Wall Unit Connection Pins
A. SRW units shall be interlocked with connection pins. The
pins shall consist of glass-reinforced nylon made for the expressed use with the SRW units
supplied.
2.03 Geosynthetic Reinforcement
A. Geosynthetic reinforcement shall consist of geogrids or
geotextiles manufactured as a soil reinforcement element. The manufacturers/suppliers of
the geosynthetic reinforcement shall have demonstrated construction of similar size and
types of segmental retaining walls on previous projects.
The geosynthetic type must be approved one week prior to
bid opening. Geosynthetic types currently approved for this project are:
________________________
B. The type, strength, and placement location of the
reinforcing geosynthetic shall be as determined by the Wall Design Engineer, as shown on
their final, sealed construction plans.
2.04 Leveling Pad
A. Material for leveling pad shall consist of compacted
sand, gravel, or combination thereof and shall be a minimum of 6 inches in depth. Lean
concrete with a strength of 200-300 psi and three inches thick maximum may also be used as
a leveling pad material. The leveling pad should extend laterally at least a distance of 6
inches from the toe and heel of the lowermost SRW unit.
2.05 Drainage Aggregate
A. Drainage aggregate shall be angular, clean stone or
granular fill meeting the following gradation as determined in accordance with ASTM D422
Sieve Size Percent Passing
1 inch 100
3/4 inch 75-100
No. 4 0-60
No. 40 0-50
No. 200 0-5
2.06 Drainage Pipe
A. The drainage collection pipe shall be a perforated or
slotted PVC, or corrugated HDPE pipe. The drainage pipe may be wrapped with a geotextile
to function as a filter.
B. Drainage pipe shall be manufactured in accordance with
ASTM D 3034 and/or ASTM D 1248
2.07 Reinforced (Infill) Soil
A. The reinforced soil material shall be free of debris.
Unless otherwise noted on plans prepared by the Wall Design Engineer, the reinforced
material shall consist of the inorganic USCS soil types GP, GW, SW, SP, SM meeting the
following gradation, as determined in accordance with ASTM D422:
Sieve Size Percent Passing
4 inch 100
No. 4 20-100
No. 40 0-60
No. 200 0-35
B. The maximum particle size of poorly-graded gravel's (GP)
(no fines) should not exceed 3/4 inch unless geosynthetic strength is reduced to account
for additional installation damage from particles larger than this maximum.
C. The plasticity of the fine fraction shall be less than
20.
PART 3: DESIGN PARAMETERS
3.01 Soil
A. The following soil parameters, as determined by the
Owner's Geotechnical Engineer shall be used for the preparation of the final design:
Unit Weight
Internal Friction
Cohesion (c)
(%) (pcf)
Angle (�) (degrees)
Reinforced Fill
________
____________
0
Retained Soil
________
____________
0
Foundation Soil
________
____________ __________
(If internal friction angles are not available for the
above section, the specifier can provide the USCS soil type classification for the
reinforced, retained, and foundation soils and/or attach the geotechnical investigation
report for this project.)
B. Should the actual soil conditions observed during
construction differ from those assumed for the design, design shall be reviewed by the
Wall Design Engineer at the Owner's Geotechnical Engineer's direction.
3.02 Design
A. The design provided by the Contractor and prepared by
the Wall Design Engineer shall consider the internal and local stability of the reinforced
soil mass and shall be in accordance with acceptable engineering practice and these
specifications. External stability including bearing capacity, global stability, and total
and differential settlement is the responsibility of the Owner or the Owner's Geotechnical
Engineer.
B. For constructability considerations, maximum vertical
spacing between geogrid layers shall be 2.0 feet.
(C.) (If the Owner wants the final wall design to be
prepared according to a particular design methodology, the design standard should be
specified here. Delete this section (C.) if not required.)
PART 4: CONSTRUCTION
4.01 Inspection
A. The Owner or Owner's Representative is responsible for
verifying that the contractor meets all the requirements of the specification. This
includes all submittals for materials and design, qualifications,
and proper installation of wall system.
B. Contractor's field construction supervisor shall have
demonstrated experience and be qualified to direct all work at the site.
4.02 Excavation
A. Contractor shall excavate to the lines and grades shown
on the project grading plans. Contractor shall
take precautions to minimize over-excavation.
Over-excavation shall be filled with compacted infill
material, or as directed by the Engineer/Architect, at the
Contractor's expense.
B. Contractor shall verify location of existing structures
and utilities prior to excavation. Contractor
shall ensure all surrounding structures are protected from
the effects of wall excavation. Excavation support, if required, is the responsibility of
the Contractor
4.03 Foundation Preparation
A. Following the excavation, the foundation soil shall be
examined by the Owner's Engineer to assure actual foundation soil strength meets or
exceeds the assumed design bearing strength. Soils not meeting the required strength shall
be removed and replaced with infill soils, as directed by the Owner's Engineer.
B. Foundation soil shall be proofrolled and compacted to
95% standard Proctor density and inspected by the Owner's Engineer prior to placement of
leveling pad materials.
4.04 Leveling Pad Construction
A. Leveling pad shall be placed as shown on the
construction drawings with a minimum thickness of 6
inches. The leveling pad should extend laterally at least a
distance of 6 inches from the toe and heel
of the lower most SRW Unit.
B. Soil leveling pad material shall be compacted to provide
a firm, level bearing surface on which to place the first course of units. Well-graded
sand can be used to smooth the top 1/2 to 1/4 inch of the leveling pad. Compaction will be
with mechanical plate compactors to achieve 95% of maximum standard Proctor density (ASTM
D 698).
4.05 SRW Unit Installation
A. All SRW units shall be installed at the proper elevation
and orientation as shown on the wall profiles and details on the construction plans or as
directed by the Engineer. The SRW units shall be installed in general accordance with the
manufacturer's recommendations. The specifications and drawings shall govern in any
conflict between the two requirements.
B. First course of SRW units shall be placed on the
leveling pad. The units shall be leveled side-to-side,
front-to-rear and with adjacent units, and aligned to
ensure intimate contact with the leveling pad. The first course is the most important to
ensure accurate and acceptable results. No gaps shall be left between the front of
adjacent units. Alignment may be done by means of a string line or offset from base line
to the back of the units.
C. Clean all excess debris from top of units and install
next course.
D. Insert two connection pins through pin holes of each
upper course unit into receiving slots
in lower course units. Pins shall be fully seated in the
pin slot below. Push units forward to remove any looseness in the unit-to-unit connection
and then check alignment. Check level and alignment of the units.
E. Lay out of curves and corners shall be installed in
accordance with the plan details or in general accordance with SRW manufacturer's
installation guidelines. Walls meeting at corners shall be interlocked by overlapping
successive courses.
F. Repeat procedures to extent of wall height.
G. The wall face cant shall not differ more than + 2
degrees from that specified.
4.06 Geosynthetic Reinforcement Placement
A. All geosynthetic reinforcement shall be installed at the
proper elevation and orientation as shown on the wall profiles and details on the final
construction plans or as directed by the Engineer.
B. At the elevations shown on the final plans, the
geosynthetic reinforcement shall be laid horizontally on compacted infill and on top of
the concrete SRW units. Embedment of the geosynthetic in the SRW units shall be consistent
with SRW manufacturer's recommendations. Correct orientation of the geosynthetic
reinforcement shall be verified by the Contractor to be in accordance with the
geosynthetic manufacturer's recommendations. The highest strength direction of the
geosynthetic must be perpendicular to the wall face.
C. Geosynthetic reinforcement layers shall be one
continuous piece for their entire embedment length. Overlap of the geosynthetic in the
design strength direction (perpendicular to the wall face) shall not be permitted.
D. Tracked construction equipment shall not be operated
directly on the geosynthetic reinforcement. A minimum of 6 inches of backfill is required
prior to operation of tracked vehicles over the geosynthetic. Turning should be kept to a
minimum. Rubber-tired equipment may pass over the geosynthetic reinforcement at slow
speeds (less than 5 mph).
E. The geosynthetic reinforcement shall be in tension and
free of wrinkles prior to placement of soil
fill. The nominal tension shall be applied to the
reinforcement and secured in place with staples, stakes or by hand tensioning until
reinforcement is covered by six inches of fill.
4.07 Drainage Materials
A. Drainage aggregate shall be installed to the line,
grades, and sections shown on the final plans. Drainage fill shall be placed to the
minimum thickness shown on the construction plans between and behind units.
B. Drainage collection pipes shall be installed to maintain
gravity flow of water outside the reinforced soil zone. The drainage collection pipe shall
daylight into a storm sewer manhole or along a slope at an elevation lower than the lowest
point of the pipe within the aggregate drain.
4.08 Backfill Placement
A. The reinforced backfill shall be placed as shown in the
construction plans in the maximum compacted lift thickness of 10 inches and shall be
compacted to a minimum of 95% of standard Proctor density (ASTM D 698) at a moisture
content within 2% of optimum. The backfill shall be placed and spread in such a manner as
to eliminate wrinkles or movement of the geosynthetic reinforcement and the SRW units.
B. Only hand-operated compaction equipment shall be allowed
within 3 feet of the front of the wall face. Compaction within the 3 feet behind the wall
face shall be achieved by at least three (4) passes of a lightweight mechanical tamper,
plate, or roller.
C. At the end of each day's operation, the Contractor shall
slope the last level of backfill away from the wall facing to direct water runoff away
from the wall face.
D. At completion of wall construction, backfill shall be
placed level with final top of wall elevation. If final grading, paving, landscaping,
and/or storm drainage installation adjacent to the wall is not placed immediately after
wall completion, temporary surface drainage shall be provided to ensure water runoff is
not directed at the wall nor allowed to collect or pond behind the wall until final
construction adjacent to the wall is completed.
4.09 SRW Caps
A. SRW caps shall be properly aligned and glued to
underlying units with Versa-Lok concrete adhesive or an equivalent, flexible,
high-strength concrete adhesive. Rigid adhesive or mortar are not acceptable.
B. Caps shall overhang the top course of units by 3/4 to 1
inch. Slight variation in overhang is allowed to correct alignment at the top of the wall.
4.10 Construction Adjacent to Completed Wall
A. The Owner or Owner's Representative is responsible for
ensuring that construction adjacent to the wall by others does not disturb the wall or
place temporary construction loads on the wall that exceed design loads, including loads
such as water pressure, temporary grades, or equipment loading. Heavy paving or grading
equipment shall be kept a minimum of three feet behind the back of the wall face.
Equipment with wheel loads in excess of 150 psf live load shall not be operated with 10
feet of the face of the retaining wall during construction adjacent to the wall. Care
should be taken by the General Contractor to ensure water runoff is directed away from the
wall structure until final grading and surface drainage collection systems are completed.
END OF SECTION
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McNear Brick and Block