PUMPING METHODS FOR DEWATERING-ALL YOU NEED TO KNOW
Drainage is the process of removal of the water from the soil. The drainage can be classified into two types which are surface drainage and sub-surface drainage. The runoff water that moves on the ground is diverged in any other direction to save the site from the flow of water. This type of drainage is known as surface drainage. If the water which is held in the pores of the soil is removed, this process is known as sub-surface drainage or dewatering.
In some places where excavation of trench is deeper and ground water table is high, the problem of water logging occurs. Sometimes the seeping water is very fast, it becomes impossible to carry excavation of the foundation. Therefore it becomes necessary to dewater the excavation area and keep it dry. The water table should be kept 0.5 m below the excavation of the foundation to keep the area dry. Several methods are available for dewatering and lowering the water table. Construction site information and types of soil are useful in deciding the economical and most suitable method for dewatering. The dewatering also improves the properties of the soil.
Purpose:
Dewatering is required for the following purposes
• To provide a dry area and permit construction to proceed efficiently. • To reduce lateral loads on sheeting and bracing in excavation.
• To reduce the pressure of air in tunneling operation.
• To control the embankment seepage in dams.
• To improve support characteristics of foundation materials.
Methods Of Dewatering
There are various methods used for controlling the groundwater during an excavation. Choosing the most suitable method of dewatering for a particular site is a critical step.
The presence of unwanted water on a construction site can lead to complications like an unsafe work area, an increase in construction cost and delay in scheduled work. So, it is important to select the right method of dewatering the undesired water on the construction site.
Well Points
Well points are a pumping system to extract the water. A well point is a perforated (with small holes throughout the perimeter) pipe. The diameter of a well point is 5 cm and it is 1 m long. The holes on the surface of the well points are covered with a screen which prevents the blockage of the perforations. The bottom of the well point is provided with a conical steel drive. It helps in the installation of the well points. There is a jetting system at the bottom of the well point. The jetting system facilitates a strong jet of water which helps in the penetration of the well points. A ball valve at the bottom of the well point helps the water jet to be in the downward direction. The well points are connected to a pipe called riser pipe which is attached to a horizontal pipe of 15 cm to 30 cm in diameter.
Deepwells
In Deepwell, one or several individual wells are drilled, and submersible pumps are placed in each shaft. The Deepwell technique is best suited for deep excavations where large water volumes need to be discharged.
Eductor
The eductor dewatering method uses an at-grade pumping station consisting of a series of small wells. The wells are equipped with nozzles, also called eductor bodies, to create a vacuum zone, drawing groundwater in through a foot-valve and piping system.
In addition to being low-maintenance once installed and cost-effective, an eductor dewatering system can reach significant depths, and isn’t limited by suction lift, so it works well for deep excavations. It’s especially useful in low-permeability soils and when close well-spacing or vacuuming is required. It is, however, unable to handle a high volume of water.
