511Riprap and Gabion Erosion Protection

Riprap and Gabion Erosion Protection

511.1DESCRIPTION

1 This section describes the requirements for constructing bank or ditch lining or slope protection.

511.2MATERIALS

1 Provide materials in accordance with the following:

Material Subsection Aggregate for Riprap 803 Filter Aggregate for Riprap 803 Geotextile 805 Gabions 811.6

511.3EQUIPMENT—V acant

511.4CONSTRUCTION

511.4.1 General

1 Submit aggregate sample in accordance with the MTM at least 14 calendar days before the use.

511.4.2 Preparation of Slopes

1 Complete excavation for and installation of riprap or gabions in dry conditions by using a non- earthen cofferdam throughout the length of the riprap or gabion sections. Cofferdam installations need to be approved by the engineer prior to excavation for riprap or gabions.

2 Shape slopes to allow for the full thickness of riprap or gabions and any bedding or filter aggregate. Slope material no steeper than its natural angle of repose. When possible, excavate the slope from undisturbed material; when not, shape and compact the underlying material to at least 90.0 percent of maximum density at optimum moisture content, in accordance with Subsection 203.4.3, Embankment and Cut Areas w ith Moisture and Density Control.

Riprap and Gabion Erosion Protection SECTION 511

511.4.3 Filter Aggregate

1 When specified, place a layer of filter aggregate on the slope immediately before placing riprap. Shape the layer to provide the minimum thickness specified and to match the bottom surface of the riprap.

511.4.4 Erosion Control Geotextile

1 When specified, place a layer of erosion control geotextile on the slope in accordance with Section 217.4, Construction, immediately before placing riprap or gabions.

511.4.5 Hand Placed Stones

1 Where hand placed stones are specified , place larger stones first and with close joints. When a footing trench is specified, place the larger rocks in the trench. Place rocks with their longitudinal axis perpendicular to the embankment face and arranged so that each rock above the foundation course has a 3-point bearing on the underlying rocks. Ensure that foundation rocks do not bear on smaller rocks used for chinking voids. Do not place rocks by dumping. Fill voids between large stones with smaller stones.

2 Use Class II unless otherwise specified in the contract.

511.4.6 Machine Placed Stones

1 Place machine-placed stones to minimize voids. Place larger stones in the toe course and on the outside surface of the slope protection. After completing the slope protection work, fill the footing trench with excavated material; the department does not require compaction.

2 Use Class II unless otherwise specified in the contract.

511.4.7 Gabions

1 Lace adjacent gabions (new-to-new and new-to-existing) along the perimeter of contact surfaces. Wire the bases of empty gabions placed on top of filled gabions tightly to the filled gabions. Stagger joints between ends of adjacent gabion baskets in a row at least 18 in [450 mm] from those in the row below.

2 Stretch the gabions in accordance with the manufacturer’s recommendations to provide proper alignment. While stretching, inspect corners for open Vs; if found, close Vs by replacing the material. Ensure that the stretching provides a resistant force to prevent bulging while installing the aggregate fill and connecting wires.

3 Place the last layer of stone in a gabion level with the top of the gabion to provide an even surface for the next course of gabions. Before placing the next course, backfill the

Riprap and Gabion Erosion Protection SECTION 511

completed course with site- excavated material in accordance with Subsection 206.4.5, Backfilling, and without displacing or damaging gabions.

511.4.8 Wire Acceptance

1 For wire products used not meeting the specification requirements for the type of wire specified, the engineer will do one of the following:

to the department;

product deducted; or

Program’s Schedule of Price Adjustment for Out-of-Specification Wire Products in effect at the time of the contract award. Obtain a copy from the Materials Program.

511.5MEASUREMENT and PAYMENT

511.5.1 General

1 The engineer will measure:

cubic yard [cubic meter] in place.

3 The department will pay as follows:

Pay Item

Pay Unit Measure to the Nearest Pay to the Nearest Filter Aggregate CY [m

] 0.1 ft [0.05 m] CY [m

] Gabions CY [m

] 0.1 ft [0.05 m] CY [m

] Gabions SY [m

] 0.1 ft [0.05 m] SY [m

] Hand-Placed Riprap CY [m

] 0.1 ft [0.05 m] CY [m

] Machine-Placed Riprap CY [m

] 0.1 ft [0.05 m] CY [m

]

511.5.2 Referenced Sections for Direct Payment

1 W hen specified , the engineer will measure and pay for erosion control geotextile in accordance with Section 217, Geotextiles.