Dewatring

Construction of buildings, powerhouses, dams, locks and many other structures requires excavation below the water table into water-bearing soils. Such excavations require lowering

the water table below the slopes and bottom of the excavation to prevent raveling or sloughing of the slope and to ensure dry, firm working conditions for construction operations.

Groundwater can be controlled by means of one or more types of dewatering systems appropriate to the size and depth of the excavation, geological conditions, and characteristics of the soil.

Construction sites are dewatered for the following purposes:

• To provide suitable working surface of the bottom of the excavation.
• To stabilize the banks of the excavation thus avoiding the hazards of slides and sloughing.
• To prevent disturbance of the soil at the bottom of excavation caused by boils or piping. Such disturbances may reduce the bearing power of the soil.

Lowering the water table can also be utilized to increase the effective weight of the soil and consolidate the soil layers. Reducing lateral loads on sheeting and bracing is another way of use.

A number of methods are available for controlling the inflow of water into an excavation; the choice of method will depend on the nature and permeability of the ground, the extent of the

area to be dewatered, the depth of the water table below ground level and the amount by which it has to be lowered, the proposed methods of excavation and ground support, the

proximity of existing structures, the proximity of water courses etc.

In middle east region most popular applicable dewatering system is Well point systems with suction pumps.