SECTION 679 – FIELDSTONE RETAINING WALL
679.01 Description This work shall consist of supplying material for and constructing a
Fieldstone Retaining Wall (FSRW) in accordance with these Specifications and in reasonably close conformity with the lines, grades, design and dimensions shown on the Plans and Special Details or as directed by the Resident. An FSRW will consist of the following components: Foundation Soils – Native soil mass supporting the FSRW Drainage System – 6-inch underdrain pipe Crushed Stone Leveling Pad - 8-inch-thick bed of Crushed Stone Wall Stones - Hard, durable, flat fieldstones or quarried stones with flat faces in a mixture of sizes to be stacked in a compact and stable mass Crushed Stone Drainage Layer – 12-inch vertical layer directly behind the FSRW Geotextile - Drainage Geotextile meeting the requirements of Standard Specification 722 Backfill - Soil placed behind the FSRW 6-221 Included in the scope of the FSRW construction are: all materials necessary for wall construction, all grading necessary for wall construction, compaction of the wall foundation soil, drainage system, crushed stone drainage layer, geotextile, backfill, construction of leveling pad, and FSRW installation. The top of the upper row of fieldstones shall be at or above the top of the face elevation shown on the Plans.
679.02 Materials Materials for FSRW shall meet the requirements of the following
sections of Division 700: Crushed Stone ¾-Inch 703.13 Gravel Borrow 703.20 Underdrain Pipe 706.06 or 706.09 Drainage Geotextile 722.02 The Contractor is cautioned that all the materials listed are not required for every FSRW. Materials shall meet the following additional requirements: 679.021 Drainage System A positive Drainage System to drain water from behind the wall shall be included in the FSRW. 679.022 Wall Stones The wall stones shall be cleaned of paint, dirt and other debris prior to use for wall construction. 679.023 Drainage Geotextile A Drainage Geotextile shall be place between the FSRW and the Backfill material as shown on Plans and Special Details in the Contract Documents. Drainage Geotextile shall consist of a geotextile approved by the Geotechnical Engineer. 679.024 Backfill Backfill material placed behind the FSRW shall meet the requirements of Section 703.20 Gravel Borrow, except that the backfill material shall only contain particles that pass the 3-inch square mesh sieve.
679.03 FSRW Requirements The FSRW layout is shown on the Plans and Special
Details in the Contract Documents. The design life of the FSRW shall be 50 years unless otherwise noted on the plans. The top of the Crushed Stone Leveling Pad shall be constructed so that the embedment depth of the FSRW is adequate to maintain stability. The minimum embedment depth to the top of the Crushed Stone Leveling Pad shall be 12 inches. A vertical Crushed Stone Drainage Layer shall be placed between the back of the FSRW stones and the backfill to promote drainage and minimize ice damage to the FSRW.
679.04 Submittals The Contractor shall submit to the Resident a Materials Certification
Letter certifying that the applicable materials for construction of the FSRW comply with this Special Provision with Section 700 of the Standard Specifications. The Contractor is required to submit a grain size distribution curve (ASTM D 422) and a moisture-density 6-222 relationship curve (AASHTO T-180) for acceptance of the proposed Backfill material. A copy of all test results performed by the Contractor or his supplier necessary to assure contract compliance shall also be furnished to the Resident. The Resident will base acceptance upon the Materials Certificate Letter, accompanying test reports, and visual inspection. No less than two (2) weeks prior to commencing construction of the FSRW, the Contractor shall submit Shop Drawings showing the details of the FSRW including plan and elevation views of the wall containing elevations at the top of the leveling pad, the distance along the face of the wall to all steps in the leveling pad, the location of the original and final ground lines, details of any steps needed, and details of the fencing at the top of the wall, if needed. All Shop Drawings shall be signed and sealed by a Professional Engineer licensed in the State of Maine. The Contractor shall submit the manufacturer’s information for the proposed Drainage Geotextile material to the Resident for approval by the Geotechnical Engineer. Drainage Geotextile material and placement shall be in conformance with the requirements of Section 620 – Geotextiles. The Contractor shall furnish the Resident a Certificate of Compliance certifying that the applicable materials comply with this Section of the Specifications.
679.05 FSRW Approval The FSRW shall be in accordance with these Specifications
and in reasonably close conformity with the lines, grades, design and dimensions shown on the Plans and Special Details, or as directed by the Resident. Construction of the FSRW shall not begin until the Contactor’s Shop Drawing have been approved by the Geotechnical Engineer.
679.06 Construction The FSRW shall be built by a skilled mason experienced in this
type of wall construction. The FSRW shall have the following construction requirements:
1.Excavation. The excavation and use as fill or disposal of all excavated material shall meet the requirements of Standard Specification Section 203 - Excavation and Embankment, except as modified herein.
2.Foundation Soils. The native soils for supporting the FSRW shall have sufficient strength to maintain global stability of the FSRW. Foundation soils shall be brought to the desired grade as required for the FSRW dimensions shown on the Plans and Special Details in the Contract Documents or as directed by the Resident. Prior to placement of the Crushed Stone Leveling Pad, the foundation soils shall be proof- rolled with multiple passes of a static roller to identify loose or weaving areas that require over-excavation and replacement and to achieve a firm and stable surface. Any loose soils or soft or unsuitable materials encountered at the bearing elevation shall be removed and replaced with Crushed Stone ¾-Inch. 6-223
4.Crushed Stone Leveling Pad. The 8-inch thick Crushed Stone Leveling Pad shall be constructed as shown on the Plans and Special Details in the Contract Documents. The Crushed Stone shall meet the requirements of Standard Specification Section 703.13. The Crushed Stone Leveling Pad shall be proof-rolled with multiple passes of a static roller to achieve a firm and stable surface. The Crushed Stone Leveling Pad shall extend at least 3 inches beyond the wall stones in all directions. Steps in the Crushed Stone Leveling Pad shall have a minimum overlap of 8 inches. The allowable elevation tolerances from the design elevations are +0.01 feet and -0.02 feet.
5.Construction of FSRW. The FSRW shall be constructed of hand fitted fieldstones or quarried stones. The stones shall be placed such that a minimum of 1.5 tons of stone is used for each cubic yard of wall. Joints shall be level and horizontal. Only short vertical joints will be allowed and no more than two vertical joints may be stacked above each other. Stones shall be stacked in a manner such that diagonal joints are kept to a minimum. Joint size in the face of the wall should be kept to a minimum and should not exceed 1.5 inches. The top of the wall should be at least 16 inches wide. The width of the base should be approximately 2/3 of the wall height, with a gradual taper from the base to the top of the wall. Stones shall be placed so the face of the wall has a minimum batter of 1H:12V. The exposed faces of each stone shall have a true plane with no projections or depressions on those surfaces greater than ½-inch. A hand fitted course of cap stones shall be placed on top of the wall. The top surface of the FSRW shall be levelled transversely, perpendicular to the wall face. This shall be constructed of stones of similar size and thickness. Each stone in the cap shall be of sufficient size to withstand accidental movement. Shims shall be placed as necessary for levelling, but shall not provide primary support for the overlying stones. Shims shall not be movable by hand. Shims shall be stone or another approved durable material and shall not be visible on the exposed face.
6.Crushed Stone Drainage Layer. A 12-inch vertical Crushed Stone Drainage Layer shall be constructed directly behind the FSRW. The Crushed Stone shall meet the requirements of Standard Specification Section 703.13. Crushed Stone Drainage Layer placement shall closely follow the erection of the FSRW.
7.Drainage Geotextile Placement. Drainage Geotextile placement shall closely follow the erection of the FSRW. Drainage Geotextile shall be placed in accordance with Standard Specification Section 620 between the native soils and the leveling pad and backfill. Drainage Geotextile seam overlaps shall be 6-inches minimum.
8.Backfill Placement. Backfill placement shall closely follow the erection of the FSRW. The backfill used behind the FSRW shall meet the requirements of Gravel Borrow, Section 703.20. Backfill shall be placed, spread, and compacted from the back of the 6-224 Crushed Stone Drainage Layer toward the limits of the excavation. Backfill shall be placed in lifts not to exceed 8 inches loose and compacted with lightweight, hand operated compaction equipment. Backfill beyond 3 feet from the back of the Crushed Stone Drainage Layer shall be compacted to 95% of the maximum density as determined by AASHTO T-180, Method C or D. Backfill compaction shall be accomplished without disturbance or displacement of the FSRW stones. Compaction adjacent to the FSRW shall be performed using hand-operated compaction equipment. Sheepsfoot rollers will not be allowed. Full size, ride on compaction equipment will not be allowed within 5 feet of the back of the FSRW. Whenever a compaction test fails, no additional backfill shall be placed over the area until the lift is recompacted and a passing test achieved. The moisture content of the backfill material prior to and during compaction shall be uniformly distributed throughout each layer and shall be within 2 percentage points dry of optimum. At the end of the day’s operations, the Contractor shall shape the last level of backfill so as to direct runoff of rain water away from the FSRW face.
679.07 Method of Measurement FSRW shall be measured by the Square Foot of front
surface not to exceed the measurements shown on the Contact Plans or as authorized by the Resident. Vertical dimension limits will be from the top of the Crushed Stone Leveling Pad to the top of the cap stone layer. Horizontal dimension limits will be from each end of the wall.
679.08 Basis of Payment The accepted quantity of FSRW will be paid for at the
contract unit price per Square Foot complete, cleaned of debris and accepted in place. Payment shall be full compensation for wall construction, compaction of the wall foundation soil, crushed stone drainage layer, backfill, drainage system, geotextile, construction of leveling pad, and FSRW installation, and other incidentals. There will be no allowance for excavating and backfilling for the FSRW beyond the limits shown on the Plans and Special Details in the Contract Documents, except for excavation required to remove unsuitable subsoil in preparation for the foundation. Payment for excavating unsuitable subsoil shall be full compensation for all costs of pumping, drainage, sheeting, bracing and incidentals for proper execution of the work and will be paid as Common Excavation in accordance with Standard Specification Section 203. Payment will be made under: P a y I t e m P a y U n i t
679.10 Field Stone Retaining Wall S q u a r e f o o t
Referenced in this section
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Source: Standard Specifications — Highways and Bridges, 2020 Edition. Pages 690–694 of 817. View official source ↗