Dewatering

There are many situations when construction is to be carried out below the ground water table. In such circumstances, excavation becomes very difficult. Either seeped water has to be pumped or the water table has to be lowered. The process of lowering the water table is called dewatering . Sometimes, we use the term pumping and dewatering together. There are many ways that the dewatering can be carried out. These can be classified as -

1. By pumping the collected water in the sump


2. By pumping water from suitably arranged well points


3. By pumping water from suitable arranged bored wells

1. By pumping the collected water in the sump - This method is commonly used in the construction where there aren't any important structures close to the excavated area and enough area is available to maintain a stable slope. In this method, one or more sumps are made at the outer boundary of the excavated site and cutting ditches around the bottom of the excavation collects water. This open sump method is generally used for construction not more that 6-7m below the water table. This method is less costly, but there are limitations. If there is fine sand lying below the water table, they get removed in seeping and causes settlement of the surrounding area. The process of open sump pumping is illustrated for foundation.