Caltrans Riprap Sizes

This has been superseded by Caltrans New Riprap Classes.

**D50 Equivalent Spherical Diameter**
RSP Class	D₅₀Size¹	D₅₀Weight
	inches	pounds
8 Ton	71	17600
4 Ton	56	8800
2 Ton	45	4400
1 Ton	36	2200
1/2 Ton	28	1100
1/4 Ton	23	550
Light	16	200
Facing	12	75
Backing No 1	12	75
Backing No 2	8	25
Backing No 3	4 2/3	5
Small RSP (7-inch)	3	1 1/3
Small RSP (5-inch)	2	2/5
Small RSP (4-inch)	1	1/20
¹Assumes rock density = 165 lb/ft³

Caltrans Standard Specifications

72-2 ROCK SLOPE PROTECTION

72-2.02A Rock

For method A placement and the class of RSP described, comply with the rock grading shown in the following table:

**Rock Grading for Method A Placement**
Rock size	Percentage larger than^a
	Class
	8T	4T	2T	1T	1/2 T
16 Ton	0–5	—	—	—	—
8 Ton	50–100	0–5	—	—	—
4 Ton	95–100	50–100	0–5	—	—
2 Ton	—	95–100	50–100	0–5	—
1 Ton	—	—	95–100	50–100	0–5
1/2 Ton	—	—	—	95–100	50–100
1/4 Ton	—	—	—	—	95–100
^aFor any class, the percentage of rock smaller than the smallest rock size must be determined on the basis of weight. For all other rock sizes within a class, the percentage must be determined on the basis of the ratio of the number of individual rocks larger than the smallest size shown for that class compared to the total number of rocks.

For method B placement and the class of RSP described, comply with the rock grading shown in the following table:

**Rock Grading for Method B Placement**
Rock size	Percentage larger than^a
	Class
	1 T	1/2 T	1/4 T	Light	Facing	No. 1	No. 2	No. 3
2 Ton	0–5	—	—	—	—	—	—	—
1 Ton	50–100	0–5	—	—	—	—	—	—
1/2 Ton	—	50–100	0–5	—	—	—	—	—
1/4 Ton	95–100	—	50–100	0–5	—	—	—	—
200 lb	—	95–100	—	50–100	0–5	0–5	—	—
75 lb	—	—	95–100	—	50–100	50–100	0–5	—
25 lb	—	—	—	95–100	90–100	90–100	25–75	0–5
5 lb	—	—	—	—	—	—	90–100	25–75
1 lb	—	—	—	—	—	—	—	90–100
^aFor any class, the percentage of rock smaller than the smallest rock size must be determined on the basis of weight. For all other rock sizes within a class, the percentage must be determined on the basis of the ratio of the number of individual rocks larger than the smallest size shown for that class compared to the total number of rocks.

Rock must have the values for the material properties shown in the following table:

**Rock Material Properties**
Property	California Test	Value
Apparent specific gravity	206	2.5 minimum
Absorption	206	4.2% maximum
Durability index	229	52 minimum

Select rock so that shapes provide a stable structure for the required section. If the slope is steeper than 2:1, do not use rounded boulders and cobbles. Angular shaped rock may be used on any planned slope. Flat or needle shaped rock must not be used unless the individual rock thickness is greater than 0.33 times the length.

72-2.02B Fabric

Fabric must be RSP fabric that complies with the class shown in the following table:

**Fabric Class**
Class	Largest rock grading class used in slope protection
8	1 ton or smaller
10	Larger than 1 ton

72-4 SMALL-ROCK SLOPE PROTECTION

72-4.02 MATERIALS

Rock must be cobble, gravel, crushed gravel, crushed rock, or any combination of these.

If the rock layer is shown as 7 inches thick, comply with grading shown in the following table:

**Rock Grading for 7-inch-Thick Layer**
Sieve sizes	Percentage passing
5 inch	100
4 inch	90–100
3 inch	25–40
2 inch	0–10

If the rock layer is shown as 5 inches thick, comply with the grading shown in the following table:

**Rock Grading for 5-inch-Thick Layer**
Sieve sizes	Percentage passing
4 inch	100
3 inch	90–100
2 inch	25–40
1 inch	0–10

If the rock layer is shown as 4-inches thick, comply with grading shown in the following table:

**Rock Grading for 4-inch Thick Layer**
Sieve sizes	Percentage passing
3 inch	100
2 inch	90–100
1 inch	25–40
3/4 inch	0–10

Granular material must contain at least 90 percent crushed particles when tested under California Test 205.