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Well point method

  • Well point method is also called as vacuum well point method.
  • The method is to place the collecting points connected to pumping pipes inside a small diameter well and arranged in a line or rectangle.
  • Multiple closely spaced wells connected by pipes to a strong pump.
  • Multiple lines or stages of well point are required for excavations more than 5m below the groundwater table.
  • The collecting points are usually separated by 0.8-0.2 m.
  • The top of the pumping pipe is connected to common collecting pipe called header.
  • Drawing out pore water from the soil and lowering the ground water level accordingly.
  • This method is a type of forced draining method.
  • The well theory is aimed at a relationship between the discharge quantity and drawdown.
  • The relationship between the discharge quantity and the drawdown can be either solved by mathematical formula or numerical ground water modeling.

Component Used in Installation of Well Point System
  • Riser pipes.
  • Swing hose.
  • Header pipe.
  • Suction hose.
  • De-watering pump.
  • Sediment tank.
  • Boosters. (if required)
  • Discharge pipe.
Well Point Types

The following will explain the basic principles and implementation

Single sided well point system.

  • Based on the water table level or ground water level the type of system can be installed.
  • In single sided well point system the system is usually installed at one side or in the middle of the site, before the excavation.
  • This is usually used in low water table or low G.W.L areas.

Double sided well point system.

  • To reduce the ground water level in and around the construction site efficiently, double sided well point system can be used.
  • In this type of dewatering system it is installed around the site based on the site area.
  • The advantage is higher rate of discharge.
  • The respective figure is below.

Double sided multistage well point system.

  • In the multi-stage well point system is used if the ground water level is higher than the excepted level.
  • This type of system is usually installed similar to as the double sided system but in tow or more stages based on site condition and G.W level.
Typical spacing, soil type and drawdown

SOIL TYPICAL SPACING TIME
SILTY SAND 1.5-2 7-21
Clean fine to coarse sand 1.0-1.5 3-10
And sandy gravel Fines to coarse gravel 0.5-1.0 1-2