🕑 Reading time: 1 minuteDewatering of excavations is required at construction sites generally for foundation works. Various methods for dewatering of excavations are described in this article. Firm and sound working conditions are indispensable when construction of buildings, powerhouse, dams, and other structures has to be executed. These structures not only require a dry base for their foundations but also good water-table stability in the girth. Dewatering of any excavated area is done in order to keep the excavation bottom dry, to prevent the leakage of water or sand and to avoid upheaval failure. Dewatering could turn out to be a herculean task if one doesn’t adopt the right method. The different methods available for dewatering of excavations at constructions sites are not necessarily interchangeable as each one has a narrow range of applications, therefore, adopting the right method of dewatering for a particular ground condition is always a critical and a difficult decision to make. A minor amount of water can always be pumped out by creating a sump but when other factors like continuous seepage, excessive smudge come into play one has to resort to a bit of sophistication.
Methods of Dewatering Excavations at Construction SiteThere are four important dewatering methods one should be aware of:
- Wellpoint method of dewatering,
- Eductor wells,
- Open sump pumping and
- Deep wellpoint method
Wellpoint Method of Dewatering Excavations1) A series of wells of required depth are created in the vicinity of the excavated area from where the water has to be pumped out. The wells are arranged either in a line or a rectangular form where the wellpoints are created at a distance of at least 2m from each other. 2) Riser pipes or dewatering pipes are then installed into those closely spaced wells which on the surface are connected to a flexible swing pipe which is ultimately appended to a common header pipe that is responsible for discharging the water away from the site. The purpose of using a flexible swing pipe is just to provide a clear view of what is being pumped and the purpose of header pipe is to create suction as well as discharge the water off the working area. 3) One end of the header pipe is connected to a vacuum pump which draws water through notches in the wellpoint. The water then travels from the wellpoints through the flexible swing pipe into the header pipe to the pump. It is then discharged away from the site or to other processes to remove unwanted properties such as contaminants. 4) The drawdown using this method is restricted to around five to six meters below the wellpoint pump level. If a deeper drawdown is required, multiple stages of wellpoints must be used.
Fig: Details of Wellpoint Method for Excavation Dewatering