284GABIONS AND SLOPE MATTRESS

283.04 Method of Measurement. Aggregate ditch will be measured for

payment in tons (metric tons) according to Article 311.08(b). Filter fabric will be measured for payment according to Article 282.08.

283.05 Basis of Payment. This work will be paid for at the contract unit price

per ton (metric ton) for AGGREGATE DITCH. Filter fabric will be paid for according to Article 282.09. SECTION 284. GABIONS AND SLOPE MATTRESS

284.01 Description. This work shall consist of furnishing and placing a

protective course of stone confined by wire baskets used as retaining walls, slope paving, bank protection, weirs, drop structures, or outfall structures.

284.02 Materials. Materials shall be according to the following.

Item Article/Section

284.03 Fabricating Gabions and Slope Mattresses. Baskets shall be

fabricated in such a manner that the sides, ends, lid, and diaphragms can be assembled at the construction site into rectangular baskets of the sizes specified and shown on the plans. Baskets furnished by the manufacturer shall be of uniform size. Baskets 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 Gabions and Slope Mattress Art. 284.05 base section of the basket in such a manner that strength and flexibility at the point of connection is at least equal to that of the mesh. Where the length of the basket exceeds 1 1/2 times its horizontal width, the basket shall be equally divided by diaphragms, of the same mesh and gauge as the body of the baskets, into cells whose length does not exceed the horizontal width. The basket 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. Baskets shall be assembled by tying or fastening all untied edges. The tying wire shall be tightly laced around every opening along the seams in such a manner that single and double loops are alternated. If wire fasteners are used, they shall be installed at approximately 4 to 6 in. (100 to 150 mm) intervals, but not less than one fastener for each opening along the joint. Sufficient wire fasteners, lacing, and connecting wire to match the basket material shall be supplied with the baskets for all fastening operations carried out in the construction of the gabion and mattress work. All perimeter edges of the baskets, including end panels and the diaphragms, if any, shall be mechanically selvedged in such a way as to prevent any unravelling of the mesh and to develop the full strength of the mesh. The wire used for the selvedge shall have a diameter greater than that of the wire used to form the mesh.

284.04 Foundation Preparation. The bed for the gabions or slope mattress

shall be trimmed and shaped to conform to the line and grade shown on the plans and as directed by the Engineer.

284.05 Placing. After the Engineer has approved the foundation preparation,

a layer of filter fabric shall be installed. Installation of the filter fabric will be required under both the gabions and the slope mattress, and behind the gabions. The filter fabric shall be installed according to the plans. The baskets shall be placed as shown on the plans. The stone material shall be placed in close contact in the unit so that maximum fill is obtained. Empty basket units shall be assembled individually and placed on the approved surface to the lines and grades as shown 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 of all creases and that the tops of all sides are level. All adjoining empty gabion units shall be secured to the adjoining unit in order to obtain a monolithic structure. Wire fasteners may be used in lieu of lacing wire for forming individual baskets, joining empty baskets together and closing lids. Binding wire or wire fasteners shall be used along vertical reinforced edges and top selvedges. When baskets are stacked, the base of the top basket shall be tightly wired or fastened to the lower basket at front and back. Lacing of adjoining basket units shall be accomplished by continuous stitching with alternating single and double loops at intervals of not more than 5 in. (125 mm). All lacing wire terminals shall be securely fastened. If wire fasteners are used, a fastener shall be provided at each opening along the joint. A minimum of six fasteners are required per 3 ft (1 m) seam, three fasteners are required per 18 in. (450 mm) seam and two fasteners per 12 in. (300 mm) seam. Art. 284.05 Gabions and Slope Mattress The initial line of basket units shall be placed on the prepared surface in a direction parallel to stream flow, and partially filled to provide anchorage against deformation and displacement during filling operations. After adjoining empty basket units are set to line and grade and common sides with adjacent units thoroughly laced or fastened, baskets 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. Stone filling operations shall carefully proceed with placement by hand or machine so as not to damage the wire coating, to ensure a minimum of voids between the stones, and the maintenance of alignment throughout the filling process. Undue deformation and bulging of the fabric shall be corrected prior to further stone filling. To avoid localized deformation, the basket units in any row are to be filled in stages consisting of maximum 12 in. (300 mm) courses. Baskets 18 in. (450 mm) tall or more shall use connecting wires in each internal compartment after each 9 or 12 in. (225 or 300 mm) lift, except when the lid is closed over the last lift. For baskets 18 in. (450 mm) tall, the connecting wires shall be installed between the 9 in. (225 m) lifts of stone. The 3 ft (1 m) tall baskets shall have connecting wires installed between each 12 in. (300 mm) lift of stone. These wires shall connect the front face to the back face. All connecting wires shall be looped around two openings and the ends of the wires securely twisted to prevent loosening. For end units, two additional connecting wires shall be placed at each level perpendicular to the normally required connecting wires. At no time shall any cell be filled to a depth exceeding 12 in. (300 mm) more than the adjoining cell. The maximum height from which the stone may be dropped into the basket units shall be 3 ft (1 m). 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 gabion 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 only an approved lid closing tool, until the lid meets the perimeter edges of the front and end panels. Using crowbars or other single point leverage bars for lid closing shall be prohibited. The lid shall then be tightly tied with lacing wire along all edges, ends, and internal cell diaphragms by continuous stitching with alternating single and double loops at intervals not more than 5 in. (125 mm). Wire fasteners may be used in lieu of lacing wire. Special attention shall be given to see that a projections or wire ends are turned into the baskets. Where shown on the plans 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 material 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. The slope mattress shall be anchored as shown on the plans. If the Contractor elects to drill for the soil anchor stakes, care shall be taken to avoid drilling holes to a greater depth than is necessary to place the top of the finished stake slightly above the top of the finished mattress. Concrete Revetment Mats Art. 285.02 The Contractor may assemble, partially fill, and tie together mattress units on the subgrade, provided they can be placed on the slope without abrading the zinc or vinyl coating on the wire mattress or permanently distorting the shape of the mattress in transporting and installing the units on the slope. All prefabrication procedures shall be subject to the approval of the Engineer. The Contractor shall maintain the gabions or slope mattress until final acceptance and any material displaced by any cause shall be replaced.

284.06 Disposal of Surplus Material. Surplus or waste material resulting

from the gabion or slope mattress operations shall be disposed of according to

Article 202 — 03.