The method of well-point dewatering and the equipment for well-point dewatering: Well-point dewatering is a method to artificially lower the groundwater level, hence it's also called the well-point dewatering method. Before excavation of the foundation pit, a certain number of filter pipes (wells) are buried around the foundation pit. Water is pumped out using pumping equipment to keep the soil being excavated in a dry state. It is generally used in construction situations where the groundwater level is relatively high. This is an important technical measure in earthwork, foundation, and subgrade engineering. It can drain water from the foundation soil, promote soil consolidation, increase the strength of the foundation, reduce lateral displacement and settlement of the soil slope, stabilize the slope, eliminate sand flow, reduce the heave of the base soil, and ensure that the foundation and subgrade construction below the natural groundwater level is not affected by groundwater. It provides a relatively dry construction condition, reduces earthwork volume, shortens the construction period, improves engineering quality, and ensures construction safety.
The well-point equipment mainly includes well-point pipes (with filter pipes at the bottom), collection main pipes, and pumping equipment, etc. The well-point pipe uses seamless steel pipes with a diameter of Φ60×5 and a length of 6.0m. At the bottom of the pipe, there is a 2.0m filter pipe. The filter pipe adopts a steel pipe with the same diameter as the well-point pipe. Between the well-point pipe and the filter pipe, there is a steel pipe coupling. A pressure-resistant rubber hose is used to connect with the collection main pipe. Holes in a plum blossom pattern are drilled on the filter pipe, with a diameter of 5mm and a distance of 15mm. The outside is wrapped with five layers of nylon mesh (100 mesh) and two layers of steel wire mesh, and 20# galvanized iron wire is wound around the outside with a spacing of 10mm.
The collection main pipe is made of seamless steel pipe with an inner diameter of 100-127mm. Each section is 4 meters long, connected by rubber sleeves, and tightened with steel hoops to prevent water leakage. Short connectors for connecting the well-point pipes are installed on the main pipe, spaced 0.8-1.2 meters apart. Each set of pumping equipment has one vacuum pump, one centrifugal pump, and one water-air separator. Each set of well-point dewatering equipment is equipped with 70 well-point dewatering pipes.
Well-point dewatering is divided into light well points, jet well points, large-diameter well points, electric seepage well points, and horizontal well points. Installation and removal of well pipes are calculated based on depth differences, with roots as units, and usage is calculated by sets and days.
(1) Composition of a set of well points:
- Light well point: 50 roots per set;
- Jet well point: 30 roots per set;
- Large-diameter well point: 45 roots per set;
- Electric seepage well point anode: 10 roots per set.
(2) The well-point spacing should be determined according to geological conditions and construction dewatering requirements, as per the construction organization design. If not specified in the construction organization design, the spacing can be determined as follows: light well-point pipe spacing of 0.8m, jet well-point pipe spacing of 2-3m.
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