§ 5.02 POROUS BACKFILL.
   Porous backfill for subdrain pipe shall conform to IDOT Specification 4131 and 4109 for gradation 29, as shown below.
 
Standard Sieve Size
1 1/2”
1”
3/4”
1/2”
3/8”
4
8
30
50
100
200
Porous backfill
100
95—100
50—100
0—50
0—8