The chief trouble in making an excavation in wet ground, is in disposing of the water and preventing the wet soil from flowing into the excavation. In moderately wet soils, the area to be excavated is enclosed with sheet piling (see Fig. 39). This piling usually consists of ordinary plank 2 inches thick and 6 to 10 inches wide, and is often driven by hand; or it may be driven by methods that will be described later. The piling is driven in close contact, and in very wet soil it is necessary to drive a double row of the sheeting. To prevent the sheeting from being forced inwards, cross-braces are used between the longitudinal timbers. When one length of sheeting is not long enough, an additional length can be placed inside. A more extended discussion of pile-driving will be given in the treatment of the subject of "Piles."

The water can sometimes be bailed out, but it is generally necessary to use a hand or steam pump to free the excavation of water. Quicksand and very soft mud are often pumped out along with the water by a centrifugal or mud pump.

Fig. 38. Drainage of Foundation Wall.

Fig. 38. Drainage of Foundation Wall.

Fig. 39. Sheet Piling in Foundation Trenches.

Fig. 39. Sheet Piling in Foundation Trenches.

Sometimes areas are excavated by draining the water into a hole the bottom of which is always kept lower than the general level of bottom of the excavation. A pump may be used to dispose of the water drained into the hole or holes.

When a very soft soil extends to a depth of several feet, piles are usually driven at uniform distances over the area, and a grillage is constructed on top of the piles. This method of constructing a foundation is discussed in the section on "Piles."