Dewatering by well point system
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A well point system consists of multiple well points spaced around an excavation site that are connected to a header pipe and pump. The well points are driven or jetted into the ground and draw groundwater into the riser pipes. This water is then pumped out through the header pipe. Spacing of well points typically ranges from 0.75m to 3m, though clay seals and sand filters can improve performance in silts. Well point systems are effective in sandy soils and can lower groundwater levels up to 5-6 meters, making them a relatively cheap and flexible dewatering option. However, they are not effective beyond 4-6 meters of drawdown and may require multiple stages.
Dewatering by well point system
- 1. Dewatering by well point system
- 2. well point system: A well point system consists of a number of well points spaced along a trench or around an excavation site, all connected to a common header which is attached to one or more well point pumps The Wells are systematically drilled around the construction area. This practice appears to work effectively for many projects, especially those building projects that require excavations for deep basements.
- 4. Setup and Procedure of working: A well-point is 5.0-7.5 cm diameter metal or plastic pipe 60 cm – 120 cm long which is perforated and covered with a screen. The lower end of the pipe has a driving head with water holes for jetting as shown in fig. Well-points are connected to 5.0-7.5 cm diameter pipes known as riser pipes and are inserted into the ground by driving or jetting. The upper ends of the riser pipes lead to a header pipe which, in turn, connected to a pump. The ground water is drawn by the pump into the well- points through the header pipe and discharged as shown in fig. The well-points are usually installed with 0.75m – 3m spacing.
- 5. Setup and Procedure of working: In gravels spacing required may be too close and impracticable. In clays it is also not used because it is too slow. In silts and silt – clay mixtures the use of well points are aided by upper (0.60m – 0.90m long) compacted clay seals and sand-filtered boreholes (20cm – 60cm diameter). Upper clay seals help to maintain higher suction (vacuum) pressures and sand filters increase the amount of discharge.
- 6. Single stage well point system
- 8. Multi stage well point system
- 10. ADVANTAGE DISADVANTAGE OF WELL SYSTEM Groundwater lowering method Advantages disadvantages Well systems 1. Effective in sandy soils 2. Provide drawdown up to 5-6 meters in sand and 4 meters in silty soil. 3. Relatively cheap and flexible 4. Installation is very rapid. 5. Water is filtered and carries little or no soil particles. 6. There is less danger of subsidence of the surrounding ground than with open-sump pumping 1. Not effective beyond 4-6 meters of drawdown 2. Might require stages of well installation.