The construction of certain structures might require excavation below the water table. When this occurs, it is important to control the groundwater, which could affect the construction project. It is important to control the water in order to complete the project and ensure safer working conditions.

Groundwater control refers to the process used to control and provide reductions in water levels for structures that must extend below the groundwater level.

The most commonly used process in achieving this is referred to as dewatering. The effectiveness of dewatering systems, however,  is largely dependent on factors such as ground conditions (soil penetrability, stability, etc.), and water level.

Dewatering includes the following techniques

a.  Sump pumping

Sump pumping is a basic method which involves digging a sump to collect groundwater and pumping the water out. This method of groundwater control is mostly used during minor excavation projects and it can be economical, but quite time-consuming to deal with.

b.  Wellpoint systems

Wellpoint systems consist of a number of small-diameter wells (horizontal or vertical), which are dug into the ground and connected with a header pipe to a wellpoint pump. The water is drawn out from the ground using a vacuum/ suction created by the wellpoint pump.

Wellpoint systems are used to reduce groundwater levels. It is a versatile groundwater control method and helps to ensure secure working conditions during the excavation process. It is also swift to set up.

c.  Siphon draining

Siphon draining involves pumping water by gravity along siphon pipes, quite similar to the process of sucking on a straw to draw out a liquid . It is most often used where there are unsteady slopes.

d.  Deep well systems

Deep well systems are often used in situations where the excavation depth surpasses the maximum levels for a wellpoint system and there is a need for a  large quantity of water to be extracted.

These systems consist of several drilled wells, with each using a borehole pump that can be operated while underwater.

e.  Ejector systems

Ejector systems operated on similar principles as well systems. They are based on wells which reduce the groundwater level to ensure safe working conditions and they enable water to be drawn out of deeper levels in the ground. Ejectors make use of air in the wells to suction water out of the soil.

f.  Vacuum wells

Vacuum wells are a reorientated type of the deep well method and they have similar operational uses as deep wells. However, there is an expectation- the submersible/ underwater pumps used in the deep well systems are supported by vacuum pumps positioned above the ground in this case.

The implementation of a vacuum pump is useful in helping to draw out water better from fine-grained soil- an action that cannot be implemented by a submersible/ underwater pump alone.

For dewatering to be successful, it must be done suitably and by experts. At Geophas Resources, we take the time to guide you through each groundwater control technique, with the aim of selecting the most suitable option for your construction project(s).

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