Backfill materials shall be permeable materials that meet the design requirements, such as gravel and crushed stone, and the gradation of permeable materials shall be reasonable. In granular materials smaller than 2cm, the content of fine materials passing through 0.074mm sieve hole is not more than 10%, and the maximum particle size of filler is not more than 50 mm
Backfilling is carried out by combining manual and mechanical methods, the part near the culvert is compacted by small machinery, and the part far away from the culvert is compacted by roller.
Subgrade filling at the top of culvert: the concrete strength of culvert can reach 100%, and when the thickness of covering soil at the top of cave is less than 1m, heavy machinery is not allowed to pass.
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