Section 253 — Gabions and Revet Mattresses

Description

253.01This work consists of constructing rock filled gabion structures and revet mattresses.

Material

253.02Conform to the following Subsections: Crushed aggregate 703.06 Gabion and revet mattress material 720.02 Gabion and revet mattress rock 705.01 Geotextile 714.01 Soil and soil- aggregate materials 704.01

Construction Requirements

253.03General . Survey a ccording to Section 152 and verify the limits of installation. Submit installation drawings according to Subsection 104.06. Conform to Section 257 for Contractor -designed gabion walls. Excavate and backfill according to Section 209. Grade the foundation for a width equal to the base width of the gabions or revet, plus any additional width shown in the plans. If required, as determined by the Contractor, design and construct temporary shoring according to Section 562. Excavate wall foundations to within 4 inches horizontally and vertically from the staked location. If shown in the plans, install underdrain system according to Section 605.

253.04Basket Assembly. Provide twisted wire or welded wire mesh baskets. Do not damage wire coatings during basket assembly, structure erection, cell filling, or backfilling. Rotate the basket panels into position and join the vertical edges with fasteners according to Subsection 253.05. Temporary fasteners may be used for basket assembly if they are supplemented dur ing structure erection with permanent fasteners according to Subsection 253.05. Rotate the diaphragms into position and join the vertical edges according to Subsection 253.05.

253.05Structure Erection. Construct gabion walls to the following tolerances:

(a)Vertical and horizontal. ±1 inch at top of wall for every 10 feet of wall height.

(b)Horizontal straight edge. ±2 inches deviation at a point in the wall from a 10 -foot metal straightedg e placed horizontally or vertically on the theoretical plane of the design face. Place the empty gabion baskets on the foundation and interconnect the adjacent baskets along the top and vertical edges using permanent fasteners. Where shown in the plans, pl ace 6 inches of compacted crushed aggregate or other specified leveling course material under the baskets. Where lacing wire is used, wrap the wire with alternating single and double loops every other mesh opening as shown in the plans or as recommended by the manufacturer and no more than 6 inches apart. Where spiral binders are used, crimp the ends to secure the binders in place. Where alternate fasteners are used, space the fasteners in every mesh opening and no more than 6 inches apart. Interconnect the base of each basket to the lids of the underlying baskets along the ends and sides of the upper basket.

253.06Cell Filling. Remove kinks and folds in the wire mesh, and properly align the baskets. Place rock carefully in the basket cells to prevent bulging of the baskets and to minimize voids in the rock fill. Maintain the basket alignment. Place stiffeners and cross- tie wires as recommended by the manufacturer in each unrestrained exterior basket cell greater than 12 inches in height. This includes int erior basket cells left temporarily unrestrained. Place stiffeners and cross- tie wires concurrently with rock placement. Fill the cells in a row to ensure no cell is filled more than 12 inches above an adjacent cell. Repeat this process until the basket is full and the lid bears on the final rock layer. Secure the lid so that no more than a 1-inch gap remains at any connection. Secure the lid to the sides, ends, and diaphragms according to Subsection 253.05. Make exposed basket surfaces smooth and neat with no sharp rock edges projecting through the wire mesh.

253.07Backfilling. Place a geotextile filter over the back face of the gabion structure according to Section 207. Concurrently with the cell filling operation, backfill the area behind the gabion structure with structural backfill according to Subsection 209.09. Compact each lift according to Subsectio n 209.10, except use an acceptable lightweight mechanical or vibratory compactor within 36 inches of the gabion structure. If using gabion basket as a free -standing roadside rockfall barrier according to Section 265, do not place a geotextile over the back face or backfill the area behind the gabion structure unless otherwise shown in the plans.

253.08Revet Mattresses. Place a geotextile filter according to Section 207. Construct revet mattresses according to Subsections 253.04 through 253.06. Anchor the mattresses in place according to the manufacturer’s recommendations. Place a geotextile filter against the vertical edges of the mattress and backfill against the geotextile filter using common backfill or the specified backfill. Overfill revet mattresses by 1 to 2 inches.

253.09Acceptance. Material for gabion structures and revet mattresses will be evaluated under Subsections 106.02 and 106.03. Construction of gabion structures and revet mattresses will be evaluated under Subsections 106.02 and 106.04. Geotextile filters will be evaluated under Section 207. Structure excavation, structural backfill, crushed aggregate, and common backfill will be evaluated under Section 209. Survey will be evaluated under Section 152. Temporary works will be evaluated under Section 562. Underdrains will be evaluated under Section 605.

Measurement

253.10Measure the Section 253 pay items listed in the bid schedule according to Subsection 109.02 and the following as applicable: When measuring gabions by the cubic yard, measure in the structure. When measuring revet mattresses by the square yard, measure the exposed face on a plane parallel to the revet mattress face.

Payment

253.11The accepted quantities will be paid at the contract price per unit of measurement for the Section 253 pay items listed in the bid schedule. Payment will be full compensation for the work prescribed in this Section. See Subsection 109.05 .