Common problems and control measures in the constr

2022-08-09
  • Detail

Common problems and control measures in the construction of bored cast-in-place piles

through the construction of Bored Piles in the retaining structure of the foundation pit of the subway station, if the qualified number obtained is greater than the minimum qualified number r required in the table, the verification experiment is carried out. Through examples, the common problems, causes and control measures in the construction of bored cast-in-place piles are briefly introduced

1. Project overview

a station of Beijing subway is an underground double-layer three span Island Station. The main body of the station is constructed by open excavation. The foundation pit is 178.4m long, the standard section is 20.9m wide, and the end shaft is 26.6m wide. The standard section of foundation pit excavation depth is 17.05m, and the end shaft is 18.03m. The main body of the station adopts the bored cast-in-place pile and rotary jet grouting pile enclosure structure. The designed pile diameter of the bored cast-in-place pile is 800mm, which is arranged along the outer wall of the station structure, and the spacing between piles is 1200mm The middle of the foundation pit is 1 × 1 pile, with a total of 229 piles with a length of 21.05m; The East and West End wells are 2# piles, with a total of 125 piles, with a length of 22.03m. The cast-in-place bored pile is poured with C25 concrete; The main reinforcement of the reinforcement cage is 3028 (double-layer), the inner reinforcement is 20, and the outer spiral reinforcement is 12

2, engineering geology and hydrology

2.1 engineering geology according to the geological survey report, the formation of the station from top to bottom, let's approach this kind of material in turn:

(1) artificial accumulation layer: silty clay fill, miscellaneous fill, bottom elevation of 45.43~42.61m

(2) recent sedimentary layer: silt, silty clay, silty fine sand and round gravel with particle size of 10~20mm, d = 200mm, distributed between the elevation of 38.09~35.28m

(3) general Quaternary sedimentary layer: silt, silty clay, bottom elevation of 36.37~32.08m; Silty fine sand, bottom elevation 35.07~30.88m; Silty clay, clay layer, silty soil layer, fine and medium sand layer, and the bottom elevation is 24.69~20.88m; Pebble and silty fine sand, with bottom elevation of 22.09~10.52m; Silty clay, clay, silt, fine and medium sand, with bottom elevation of 10.79~7.63m; Silty fine sand and silty clay, with bottom elevation of 8.38~7.03m

2.2 hydrogeology

(1) phreatic water: the aquifer is mainly round gravel and silty fine sand, with good water permeability, and the water level elevation is 39.51~41.59m. Therefore, the water level should be professional in maintenance. The buried depth is 4.50~6.50m, which is located in the station hall layer of the station structure. This layer of groundwater is closely related to the surface water system. Due to the leakage of nearby ponds and lakes, this layer of groundwater is directly recharged by surface water

(2) the first layer of confined water. The aquifer is mainly silty soil and silty fine sand, with general water permeability. The water level elevation is 32.41~35.88m, and the buried depth of the water level is 10.10~13.50m. It is located at the upper part of the platform layer of the station structure, and the head height is 1~4m The first layer of confined water is closely related to surface water and phreatic water

(3) confined water in the second layer. The aquifer is mainly composed of pebble and silty fine sand layer with large permeability coefficient, which is a strong permeable layer. The water level elevation is 29.33~33.13m, and the buried depth of the water level is 13.00~16.40m. It is located at the lower part of the platform layer of the station structure. Do not use SW plug with other electrical machinery, and the head height is 7~9m

3. Construction arrangement

according to the requirements of the construction period, in order to speed up the progress of the project and improve work efficiency, combined with the site and geological and hydrological conditions, the construction method of rotary drilling rig construction and vertical tremie pouring concrete piles is adopted. In addition, an impact drill (only used as an auxiliary, when the rotary drilling rig is difficult to pass through the pebble and round gravel stratum, the impact drill can be used) is equipped to cooperate with the construction. In order to prevent the hole collapse caused by the distance between the two piles being too close or the time interval being too short during drilling, the construction sequence of skipping holes in batches shall be adopted for each interval of two holes

Copyright © 2011 JIN SHI