Erosion and Sediment Pollution Control Program Manual.pdf

Riprap Specifications - Rock utilized for riprap should consist of sound, durable rock, insoluble in water.
Note: This does not exclude limestone since the rate of dissolving for limestone is very low for nonacidic
waters. Riprap should be free of structural defects, shale seams, and foreign materials such as
quarry dust, soil, shale, and organic matter. Individual pieces should be sharply angular, whenever
possible, block-shaped and have a minimum specific gravity of 2.5. Where rock is used having
average unit weights that vary significantly from 165 lb/ft 3 , the size of the individual pieces should be
adjusted according to Table 6.8. No piece should have a length exceeding three (3) times its width or
depth. Each load should be well-graded from the smallest to the largest stone size. Pieces smaller
than the minimum size may not exceed 15% of the tonnage shipped. Minimum placement thickness
should be equal to 1.5 times the maximum stone size (dmax).
TABLE 6.8
Riprap Size Adjustment Factor for Various Rock Types
Rock Type
Average Unit Weight
(lb/ft 3 ) Adjustment Factor
Diabase 184 0.5
Granite 167 1.0
Limestone 165 1.0
Sandstone
PA DEP
151 1.5
Example: To use riprap composed of sandstone, multiply the maximum, minimum and d50 stone sizes
from Table 6.6 by 1.5. Thus, for an R-5 sandstone riprap, the maximum stone size should be 27”, the
d50 stone size 13.5”, and the minimum stone size 6”. Since quarries generally grade rock riprap to the
common “R” sizes, in this example the sandstone would need to be an R-6 gradation.
PA DEP
363-2134-008 / March 31, 2012 / Page 136