BICSI OSP Design Practice Test

A gravel bed under manholes and pedestals is used to provide drainage, create a stable bed for cables and ducts, and help control settlement during backfilling. Six inches of clean gravel is the standard depth because it strikes a balance between adequate drainage and usable space inside the MH/pedestal. Four inches wouldn’t reliably drain moisture or cushion the cables, while eight or ten inches adds unnecessary cost and reduces usable volume without additional benefit. Therefore, six inches is the best, most practical choice.