Source: FP-14 Standard Specifications
Author: FHWA
Table 705-1 Gradation Requirements for Riprap(1)
Class % of Rock Equal or Smaller by Count Range of Intermediate Dimensions,(2) Range of Rock Mass,(3)
DX inches (millimeters) pounds (kilograms)
1 100 9 – 15 (230 – 380) 59 – 270 (27 – 120)
85 7 – 11 (180 – 280) 28 – 110 (13 – 50)
50 5 – 8 (130 – 200) 10 – 42 (5 – 19)
15 3 – 6 (80 – 150) 2 – 18 (1 – 8)
2 100 15 – 21 (380 – 530) 270 – 750 (120 – 340)
85 11 – 15 (280 – 380) 110 – 270 (50 – 120)
50 8 – 11 (200 – 280) 42 – 110 (19 – 50)
15 6 – 8 (130 – 200) 10 – 42 (6 – 19)
3 100 21 – 27 (530 – 690) 750 – 1600 (340 – 730)
85 15 – 19 (380 – 480) 270 – 560 (120 – 250)
50 11 – 14 (280 – 360) 110 – 220 (50 – 100)
15 8 – 10 (200 – 250) 42 – 81 (19 – 37)
4 100 27 – 33 (690 – 840) 1600 – 2900 (730 – 1300)
85 19 – 23 (480 – 580) 560 – 990 (250 – 450)
50 14 – 17 (360 – 430) 220 – 400 (100 – 180)
15 9 – 12 (230 – 300) 59 – 140 (27 – 64)
5 100 33 – 39 (840 – 990) 2900 – 4850 (1300 – 2200)
85 23 – 28 (580 – 710) 990 – 1800 (450 – 820)
50 17 – 20 (430 – 510) 400 – 650 (180 – 290)
15 11 – 15 (280 – 380) 110 – 270 (50 – 120)
6 100 39 – 45 (990 – 1140) 4850 – 7400 (2200 – 3350)
85 28 – 32 (710 – 810) 1800 – 2650 (820 – 1200)
50 20 – 23 (510 – 580) 650 – 990 (290 – 450)
15 13 – 17 (330 – 430) 180 – 400 (82 – 180)
7 100 45 – 54 (1140 – 1370) 7400 – 12,800 (3350 – 5800)
85 32 – 38 (810 – 970) 2650 – 4450 (1200 – 2000)
50 23 – 28 (580 – 710) 990 – 1800 (450 – 820)
15 15 – 20 (380 – 510) 270 – 650 (120 – 290)
8 100 54 – 66 (1370 – 1680) 12,800 – 23,400 (5800 – 10,600)
85 38 – 47 (970 – 1190) 4450 – 8450 (2000 – 3850)
50 28 – 35 (710 – 890) 1800 – 3500 (820 – 1600)
15 19 – 25 (480 – 640) 560 – 250 (250 – 570)
9 100 66 – 78 (1680 – 1980) 23,400 – 38,600 (10,600 – 17,500)
85 47 – 55 (1190 – 1400) 8450 – 13,500 (3850 – 6100)
50 35 – 41 (890 – 1040) 3500 – 5600 (1600 – 2550)
15 22 – 30 (560 – 760) 870 – 2200 (390 – 1000)
10 100 78 – 90 (1980 – 2290) 38,600 – 59,300 (17,500 – 26,900)
85 55 – 64 (1400 – 1630) 13,500 – 21,300 (6100 – 9650)
50 41 – 48 (1040 – 1220) 5600 – 9000 (2550 – 4100)
15 26 – 36 (660 – 910) 1450 – 3800 (660 – 1700)
(1) Gradation includes spalls and rock fragments to provide a stable, dense mass.
(2) The intermediate dimension is the longest straight-line distance across the rock that is perpendicular to the rock’s longest axis on the rock face with the largest projection plane.
(3) Rock mass is based on a specific gravity of 2.65 and 85 percent of the cubic volume as calculated using the intermediate dimension.

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