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Backfilling Box Culvert

A guide to backfilling

Backfilling should start as soon as possible after the box culverts have been laid.  The trench should be filled to the level of the top of the culvert, filling evenly on each side as backfilling progresses. Special care should be taken to not disturb the box culvert alignment. Heavy vibratory equipment should never be used.  The fill should be done in well compacted layers with layers not exceeding approximately eight inches. After backfilling to the top of the box, continue covering the box with compacted layers until the trench is completely backfilled. No heavy equipment should be driven over the installed culvert prior to checking that the structure is designed to withstand the loads. The backfill material, percent of compaction, depth of layers, etc. should follow the project specifications.

In multi-cell applications where box sections are installed in parallel, a means must be provided to ensure continuous lateral bearing between the adjacent boxes. Compacted earth fill, granular backfill, or grouting between the units are acceptable means of providing continuous lateral bearing between the adjacent boxes.