Page 239 - Moving the Earth_ The Workbook of Excavation

DITCHING AND DEWATERING

DITCHING AND DEWATERING 5.41

FIGURE 5.30 Load over pipe.

In (B), backfill has been placed loosely over an exposed or projected pipe. Settlement under
traffic, or from the effects of weather, will be a fraction or percentage of its depth, so that the thin-
ner fill over the pipe will not sink as far and will project as a surface ridge. This ridge may receive
heavier loads, and be more thoroughly compacted, than the soil on each side.
If a trench is loosely filled, settlement will result in a surface trough. Vehicles bumping across
this will cause heavy impact loads. If the pipe is near the surface, it may be damaged or destroyed.
If deep, the loads will largely be carried by the walls.
A tightly tamped backfill should distribute loads evenly over the whole area and subject the
culvert to normal loads for its depth, as in (A).
Whatever load is imposed on the immediate vicinity of the pipe will be shared by it and by the
fill on each side. If the fill is tightly tamped, it will bear a larger part of the burden, relieving the top
of the pipe. Vertical pressure on the side fill is partly converted into horizontal pressure against the
sides of the pipe, providing support for the top load.