EXCAVATIONS: Ditches and Sumps.

This is the simplest form of dewatering used in shallow excavations in coarse grained soils. Shallow pits, called sumps are dug along the periphery of the area-drainage ditches. The water from the slopes or sides flows under gravity and is collected in sumps from which it is pumped out [Fig. 2.35(a)]. If the seepage (ie. flow of water) is significant, it may cause softening and revelling or sloughing of the lower part of the slope. There is also possibility of piping in the sump bottom, because of upward flow. In such circumstances, the sump can be weighted down with an inverted filter consisting of layers of successively coarser material from the bottom of the sump-pit upwards [Fig. 235(b)].

FIG. 2.35 EXCAVATION DRAINAGE WITH SUMP.