Discussion on construction of special parts in concrete construction（1）
1 Foundation pit dewatering
1.1 Tube well layout
Foundation pit side: pipe well foundation pit side layout, spacing 15m, about 5m away from the pit.
Inside the foundation pit: about 5m away from the edge of the pit, the tube Wells are arranged in the shape of plum blossom, with an interval of 15m.
Length of tube well: combined with the depth and width of foundation pit, the length of tube well is about 25m.
According to the characteristics of the bottom layer of the project, the dewatering well construction should be carried out before the earthwork excavation. According to the conventional experience, 510 well pipe dewatering is proposed to be adopted, and the dewatering area of each well is 350 square meters.
1.2 tube well construction
Water well construction should pay attention to the following requirements:
Hole making: the mud retaining wall of bit 770 is adopted to make holes with positive circulation, the hole diameter shall be no less than 800mm, the hole forming deviation shall be less than 1/500, the depth shall be at least 1m more than the hole depth to facilitate sediment, and the mud specific gravity shall be controlled under 1.15m.
Slurry change: the mud in the hole should be diluted before filling in the filter material. The mud density should be less than 1.15, the sand content should be less than 5%, and the viscosity should be less than 28S.
Down the well pipe: when down the well pipe, it is required to check whether the filter mesh is complete and whether the winding wire is broken.The bottom of the first well pipe shall be sealed with steel plate. The welding of the well pipe shall be required and welded with 10cm long steel bar to prevent the fracture of the well pipe.Each seam is welded with 5 pieces, and a centralizer is set every 4m.The well pipe is 30cm above ground. It is strictly forbidden to force the well pipe into the well.
Gravel filling: when filling, the wellhead should be sealed with gunny-bag and other materials. Mung bean sand should be poured evenly around the wellwall. The amount of gravel should be 0.95 times larger than the calculated amount.
Well washing: well washing is an important process of well drilling. After the completion of filling, it is advisable to timely use the bucket combined with the piston to wash the well and repeatedly wash the well until the clean water comes out. The well washing time shall be no less than 4 hours.After the completion of well washing, the water pump should be lowered in time to draw water, determine the water amount of a single well, and the sediment in the well should not exceed 1.0m.
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