Study On Groundwater Extraction In Open-cut Foundation Pit In Sandy Pebble Soil Strata And Control Of Ground Subsidence

As the city develops,the ground buildings become more and more dense,and construction sites in cities are increasingly restricted by space.In order to reduce the impact of construction on surrounding buildings,a series of measures are taken during construction.During the construction of deep foundation pits of subway stations,the groundwater level in the foundation pit is generally reduced by the outer tube wells of the foundation pits.However,due to the dense construction facilities in the city and the influence of groundwater extraction on the surrounding buildings,the method of groundwater extraction in the foundation pit can be used to achieve the purpose of foundation pit dewatering construction.At present,the calculation of dewatering design is based on the design of the outside foundation pit.Therefore,this paper studies the design method of groundwater extraction in the foundation pit,and theoretically calculates the influence of dewatering on the ground subsidence around the foundation pit,and uses the finite difference numerical simulation to carry out foundation pit groundwater extraction and excavating process,and the subsidence curve of the ground surface outside the foundation pit is obtained.The specific research content is as follows:(1)Based on the existing calculations,a design method for groundwater extraction in foundation pit is proposed and applied in the open excavation of the subway station of Chengdu Metro Line 6 to guide the layout of the project;(2)The calculation method of the surrounding ground subsidence respectively applies the methods of norm and considering the effect of seepage force,And the calculated ground subsidence values are compared with the on-site monitoring values.The results show that the algorithm of the effect of seepage force is more accurate.(3)The finite difference method is used to simulate the foundation pit dewatering process.The surrounding ground subsidence caused by groundwater extraction in the foundation pit under single well and group wells layout is studied.The effect of group wells of the ground subsidence around the foundation pit caused by groundwater extraction in the foundation pit was discussed.(4)The finite difference method is used to simulate the whole process of groundwater extraction and excavation in the foundation pit.The variation trend of groundwater level around the foundation pit under different dewatering depths is studied,and compares with the theoretically dewatering funnel curve.At the same time,under different excavation depths and dewatering depths,the subsidence values of the ground around the foundation pit are compared and analysed with on-site monitoring and theoretical calculations.After the excavation of the foundation pit is completed,the ground subsidence range around the foundation pit is discussed,and the subsidence ratio caused by groundwater extraction in the maximum ground subsidence value is proposed.