657.01 Description. This work consists of furnishing and placing riprap for protecting selected trees or shrubs by tree wells and retaining walls.
657.02 Materials. Furnish stone consisting of sandstone, limestone, or other natural rock with a maximum 30 percent single slab loss and a maximum 20 percent cumulative loss after testing to ASTM D 5240. Use an 8-inch slab test sample. The Department may waive testing when the stone source has a known durability history. Furnish embankment according to Item 203. Unless otherwise specified, use 4-inch (100 mm) pipe conforming to 603 Type E conduits.
657.03 Tree Wells in Fill. Where a fill around a tree or shrub not marked for removal will be 12 inches (0.3 m) or more in depth over the feeding root area or ground surface lying within the periphery of the tree, construct a dry hand-laid stone riprap tree well. Construct a wall, of the same height as the fill, circling the tree or shrub and 3 1/2 feet (1 m) from the tree trunk or as specified. Construct the wall so that the top of the wall follows the contour on the finished grade in a neat line.
Construct tree wells before placing the fill over the root area. However, the Contractor may bring up the fill with the wall after required aggregate for root aeration is in place according to Item 658.
657.04 Walls in Cut. Where the top of the slope in cut is within 6 feet (2 m) of the trunk of a tree not marked for removal, construct a dry hand-laid stone riprap wall. Toe the bottom of the wall into the ground 2 inches (50 mm) unless otherwise shown on the plans, and make the top of the wall even with the original ground line at the base of the tree. Extend the length of the wall far enough from the tree to amply cover the roots, or according to the shape and size as shown on the plans. Flare the ends of the wall back, and taper or fade them out into the finished grade of the slope in a neat line.
657.05 Hand-Laid Stone Riprap. Construct the earth bed on which riprap is to be placed to a slope of 1 foot (300 mm) vertical to 2 inches (50 mm) horizontal. Dress the earth bed to a true plane. Where riprap is to rest against a fill, tamp the embankment against the back of the stone.
Construct riprap for walls or wells according to the arrangements and dimensions shown on the plans. Lay each course with the long dimensions of each stone perpendicular to the slope or batter.
Use individual stones that are roughly rectangular in cross-section and are a minimum of 3 inches (75 mm) in the vertical depth with a horizontal dimension of not less than 15 inches (0.4 m). Place the individual stones by hand, one upon the other so that they break joints with the stone in the course below. Where it is necessary to use more than one stone to provide the specified thickness or depth of the wall, thereby resulting in joints parallel to the face of the wall, place such stones to break joints with the adjacent stones.
Fill the space between the larger stones with spalls rammed into place. Ensure that the surface of the finished riprap does not vary more than 3 inches (75 mm) from that shown on the plans, and that it presents an even, tight surface, pleasing in appearance.
657.08 Method of Measurement. The Department will measure Riprap for Tree Protection by the number of square yards (square meters) in place, completed and accepted. The Department will measure parallel to the face of the wells or walls.
The Department will pay for accepted quantities at the contract price for as follows:
Item unit Description
Yard Riprap for Tree Protection