enc2_BRH_SupSpecs_Adendum_gjk_06302015.pdf

AG-569R-S-15-0037 Black River Harbor Retaining Wall Improvements

Amendment 1 Enclosure 2

253 – Gabions and Revet Mattresses

Insert section in its entirety

1.0 Description

This section covers the furnishing, assembling, filling with stone and tying open wire mesh rectangular compartmented gabions placed on filter cloth or filter stone as specified herein, and in reasonably close conformity with the lines, grades, dimensions, and cross- sections shown on the plans or as directed by the Engineer, and the design, working drawings, materials, construction, measurement and payment for gabions.

Included in the scope of this section are: grading and compaction of the wall foundation, general and local dewatering as required for proper execution of the work, installation of wall drainage systems as specified on the plans, erection of units, the placement of stone within the units and compaction of the soils behind the units as well as the construction of any required reinforced concrete appurtenances such as caps, copings, or end sections as specified on the plans. For the purposes of this section, the gabions foundation shall include all areas underlying the gabion wall.

2.0 Design Criteria

The current AASHTO Standard Specifications for Highway Bridges with Interim

Specifications shall be used as the basis for design.

3.0 Materials

3.1 Stainless Steel Wire Mesh

Gabion basket units shall be of non-raveling construction and fabricated from a double twisted hexagonal mesh of stainless steel wire having a minimum diameter of 0.118 inches. All gabion diaphragm and frame wire shall equal or exceed ASTM A 853, ASTM A 818, ASTM A 641, ASTM A 809 and possess an average tensile strength of 60,000 PSI. Mesh openings shall be rectangular in shape, and uniform in size measuring not more than 3-1/4 inches by 4-1/2 inches.

Selvedge or perimeter basket frame wire shall be of heavier gauge than the wire mesh with a minimum diameter of 0.1535 inches.

Wire used for lacing or as internal connecting wire within basket cells shall meet the same specifications described above for the mesh wire, except that it may be of lighter gauge with a minimum diameter of 0.0866 inches It shall be capable of resisting deleterious effects of natural weather exposure, immersion in salt water and shall not show any material difference in its initial characteristics.

3.2 Stone Fill

All stone fill shall be approved by the Engineer and shall be of suitable quality to ensure durability. When the stone is subjected to five alterations of sodium sulfate soundness testing, in accordance with AASHTO T-104, the weighted percentage of loss shall not be more than twelve percent. The inclusion of objectionable quantities of shale, dirt, sand, clay, rock fines, and other deleterious material will not be permitted. Stone fill shall be of well-graded mixture with sizes ranging between 4 inches and 8 inches in diameter, based on U.S. Standard square mesh sieves. No stone shall have minimum dimension less than 4 inches. All stones shall have rounded surfaces and have a color in similarity as shown in Figure 1. Stone fill material selected for use in the gabions shall meet the minimum in-place density specified on the plans.

3.3 Geotextile Fabric

The separating geotextile woven fabric shall be rated to 8 to 10 oz. and in accordance with details as shown on the plans.

4.0 Construction

4.1 Clearing and Grubbing

Clearing and grubbing, removal of structures and obstructions, and excavation and undercutting shall be performed in accordance with the provisions of Sections 201, 202, and 203, respectively, of the Standard

Specifications. Cost of these items, however, shall be included in the square foot price bid retaining walls as shown in contract plans.

4.2 Foundation Preparation

Foundation preparation for the gabions shall be made to the required depth below the finished surface and to such a width as to permit the proper installation of the gabions. Prior to wall construction, the top 12 inches of the foundation shall be compacted to at least 95% of maximum laboratory dry density as specified in AASHTO T 99. All soft and unsuitable material shall be removed and replaced with suitable material, which shall then be compacted. The finished subgrade shall be smooth and uniform, with no protruding debris or rock formations.

A Size 57 stone may be required to obtain the smooth uniform surface and shall be in reasonably close conformity with the dimensions and designs shown on the plans or established by the Engineer. No gabions shall be constructed upon frozen foundation material.

4.3 Geotextile Fabric

Upon final foundation preparation and acceptance by the Engineer, the geotextile fabric shall be placed directly on the foundation at those locations shown on the plans or as directed by the Engineer. All end and side laps shall be a minimum of 18 inches for the fabric

4.4 Assembly (Fabrication)

Gabions shall be fabricated in such a manner that the sides, ends, lid, and diaphragms can be assembled at the construction site into rectangular baskets. Gabions shall be of single unit construction, i.e., the base, lid, ends, and sides shall be either woven into a single unit or one edge of these members connected to the base section of the gabion in such a manner that strength and flexibility at the point of connection is at least equal to that of the mesh. Gabion units shall be equally divided, by diaphragms of the same mesh and gauge as the body of the gabions, into cells whose length does not exceed the horizontal width. The gabion shall be furnished with the necessary diaphragms secured in proper position on the base in such a manner that no additional tying at this juncture will be necessary. All perimeter edges of the mesh forming the gabion shall be securely selvedged so that the joints formed by tying the selvedges have at least the same strength as the body of the mesh. Lacing wire or connecting wire shall be supplied in sufficient quantity for securely fastening all diaphragms and edges of the gabion.

4.5 Assembly (Field)

Empty gabion units shall be placed on the filter blanket when required on contract drawings and shall be assembled individually to the lines and grades indicated on the Plans or as directed by the Engineer, with the sides, ends, and diaphragms erected in such a manner to ensure the correct position. All adjoining empty gabion units must be connected by tie wire lacing along the perimeter of their contact surfaces in order to obtain a monolithic structure. Lacing of adjoining basket units shall be accomplished by continuous stitching with alternating single and double loops at intervals of not more than 5 inches. All lacing wire terminals shall be securely fastened. The use of expedient clip connections for this purpose or as final lid closing will not be permitted. After adjoining empty basket units are set to line and grade and common sides with adjacent units thoroughly laced, they shall be placed in tension and stretched to remove any kinks from the mesh and to a uniform alignment.

The stretching of empty basket units shall be accomplished in such a manner as to prevent any possible unraveling and distortion.

Stone filling operations shall carefully proceed with placement by hand or machine to assure a minimum of voids between the stones, to prevent damage to the underlying filter blanket, and to ensure the maintenance of alignment throughout the filling process. The maximum height from which the stone may be dropped into the basket units shall be 36 inches. Along all exposed faces, the outer layer of stone shall be carefully placed and arranged by hand to ensure a neat and compact appearance.

The last layer of stone shall be leveled with the top of the gabions to allow for the proper closing of the lid and to provide an even surface that is uniform in appearance.

Lids shall be stretched tight over the stone fill using crowbars or lid closing tools until the lid meets the perimeter edges of the front and end panels.

The lid shall then be tightly laced with tie wire along all edges, ends and internal cell diaphragms by continuous stitching with alternating single and double loops at intervals of not more than 5 inches. Special attention shall be given to see that all projections or wire ends are turned into the baskets.

Where shown on the drawings or as directed by the Engineer, or where a complete gabion unit cannot be installed because of space limitations, the basket unit shall be cut, folded and wired together to suit existing site conditions. The mesh must be cleanly cut and the surplus mesh cut out completely or folded back and neatly wired to an adjacent gabion face. The assembling, installation, filling, lid closing, and lacing of the reshaped gabion units shall be carried out as specified above.

4.6 Backfill

Backfilling of the gabion wall shall follow erection as closely as possible and in no case should the height of the wall be greater than seven feet above the backfill. Underdrains, if required, shall be placed in accordance with the details shown on plans. Gabion walls backfill shall have a density of 100 pounds per cubic foot or as specified on contract plans and shall be compacted to at least 95 percent of the maximum laboratory dry density as defined in AASHTO T 99 to within one foot of the top of the wall. The top

12 inches shall be compacted to at least 100 percent of the maximum laboratory dry density. Prior to placement, the backfill material must be approved by the Engineer. The Contractor shall furnish, install, operate, and maintain satisfactory dewatering system as required to maintain the site in a dry and workable condition so as to permit grading and compaction of the wall foundation and proper erection and backfill of the wall. These systems shall include all equipment and materials, and shall be continued as long as necessary.

No separate measurement or payment will be made for dewatering or dewatering systems.

4.7 Vertical Wall Tolerance

The overall vertical tolerance of the wall (plumbness from top to bottom) shall not deviate more than ½ inches per 10 feet of wall height from the contract drawings batter of the wall.

4.8 On Site Inspection

The quality of materials, the process of manufacture, and the finished members shall be subject to inspection and approval by the Engineer.

Any gabions damaged prior to acceptance shall be repaired or reconstructed as directed by the Engineer. All costs of repairs or reconstruction shall be at the Contractor’s expense.

4.9 Final Cleanup

Final cleanup shall be performed in accordance with the requirements of

Section 106 of the Standard Specifications.

5.0 Equipment

All equipment necessary for the satisfactory performance of the construction of stone- filled gabions shall be approved by the Engineer before construction will be permitted to begin.

5.0 Method of Measurement

Gabion walls will be measured by the square foot of surface area of the wall face.

6.0 Basis of Payment

Payment for gabion walls will be as outlined on the contract drawings and shall be full compensation for pre-construction engineering, preparation of plans and working drawings, excavation, sheeting, shoring, foundation preparation, drainage, filter blanket, wire mesh baskets, tying, stone fill, erection of units, miscellaneous hardware, select backfill, presplitting, shaping of cuts, bituminous fiberboard and all miscellaneous materials and labor required for complete approved installation of gabions.

Additional area of wall required due to unforeseen conditions or other reasons and approved by the Engineer will be paid for on the basis of the unit price bid. If required for retaining wall protection against vehicle impact, the cost of the barrier wall and end terminals shall be included in the square foot cost of the wall.

Figure 1. Photo showing rock color to match.