Support design of a foundation pit in Luohu District, Shenzhen Construction plans
Content introduction I. Engineering geological and hydrogeological conditions The proposed xx site is located in the north of xx Road, Luohu District, On the east side of xx Road, the original landform of the site is monadnock slope, which has not been leveled yet. The terrain is high in the north and low in the south. According to the drilling exposure, the rock and soil layers of the site are from top to bottom: fill layer, Quaternary alluvium and proluvium layer, Quaternary eluvium layer and Sinian bedrock. The burial distribution law and change characteristics from top to bottom are: 1. Miscellaneous fill, consisting of clay, concrete blocks, brick, granite, gravel The construction waste such as block stones is backfilled with a small amount of domestic waste in some places, which is loose and uncompacted, with a distribution thickness of 0.8~2.2m and an average thickness of 1.53m. 2. Silty clay, plastic to hard plastic, contains a lot of silt, and locally distributed with gravels and pebbles at the bottom, with a thickness of 1.5~2.2m and an average thickness of 1.73m. 3. Fine sand, saturated, moderately dense, containing more clay and 5~10% pebbles, distributed only in ZK7, with a thickness of 4.0m. 4. Residual cohesive soil layer, plastic hard, mainly composed of clay and quartz, is 12.1~31.9m thick, with an average thickness of 21.16m. The groundwater in the site includes Quaternary pore water and bedrock fissure water. The pore water is stored in the pores of the soil layer, with poor water quantity and poor permeability of the soil layer. 2、 Design description 1. The ± 0.000 absolute elevation of the project is temporarily 9.9 meters, and the relative elevation of the north side of the site is about 0.5~1.6 meters. It is leveled to -0.6 meters before formal construction. The relative ground elevation of the sidewalk on the west, east and south sides of Zhongxing Road is about -0.60m, the excavation elevation of foundation pit is temporarily -8.8m, and the support elevation is temporarily -9.4m (bottom of ground beam cushion). The safety level of foundation pit support is Level II. 2. According to the requirements of the construction party, the periphery of the foundation pit is excavated vertically. 3. According to the site stratum conditions, hydrogeological conditions, surrounding environmental conditions and engineering experience of adjacent projects, the foundation pit is proposed to adopt the composite soil nailing wall enclosure structure under the condition of root pile advance support. 4. The underground water in the site is poor, and the excavation scope is relatively impermeable except for the surface layer. Therefore, during the excavation of the foundation pit, it is not necessary to use a water stop curtain or a dewatering well to reduce the underground water level. The underground water is treated by open drainage. 5. The drainage ditch is built with lime sand bricks at a proper position on the top of the foundation pit to intercept the surface water. The slope top drainage ditch is connected with the municipal drainage system through the sedimentation tank; The drainage ditch is built with lime sand bricks along the slope toe line at the bottom of the foundation pit, and the collecting wells are set at the corners of the bottom of the foundation pit to drain the accumulated water in the foundation pit.
