(A) Backfill gradation requirements. Material shall be granular, consisting essentially of sand, gravel, rock, slag, disintegrated granite or a combination of such materials. It shall be a well graded mixture containing sufficient soil mortar, crusher dust or other binding materials which, when placed and compacted, will result in a firm, stable foundation. Material composed of uniformly sized particles or which contains pockets of excessively fine or excessively coarse material will not be acceptable. The backfill material shall meet the following gradation:
Sieve Designation | Percent By Weight Passing |
2.5 inch | 100 |
2 inch | 95—100 |
No. 40 | 30—60 |
No. 20 | 5—15 |
(B) Liquid and plasticity standards.
(1) All material passing the No. 40 sieve shall have a liquid limit of not over 35 and a plasticity index of not over six. Test for a liquid limit and plasticity index shall be in accordance with AASHTO designations T-89 and T-91 respectively.
(2) Six inches of Colorado Department of Highway’s class 6 aggregate base course will be required on top of the subgrade material. The class 6 ABC shall meet the following gradation:
Sieve Designation | Percent By Weight Passing |
1 inch | 100 |
3/4 inch | 95—100 |
1/2 inch | 20—55 |
3/8 inch | 0—15 |
No. 4 | 0—5 |
(Ord. 7(1971) § 5(A)(1)(a); Ord. 8(1991) § 6)