Influence Of Dewatering Excavation Of Foundation Pit On Surrounding Environment Of Xuzhou Metro Line 1 Station And Its Control Method

In recent years,with the rapid development of economy and society,the construction of subway has become the top priority in the future development.As a thoroughfare and cultural city of five provinces,Xuzhou has also ushered in the upsurge of subway construction,which is of great significance to the economic and social development of Xuzhou.However,the subway construction inevitably needs to excavate the tunnel.Once the tunnel is excavated,the buildings and facilities around the tunnel will be damaged.Therefore,it is very important to pay attention to the stability of the foundation pit excavation.Based on the deep foundation pit engineering of Shizishan station in No.06 bid section of Xuzhou Metro Line 1,through the means of field investigation and data survey,the surface settlement mechanism caused by dewatering and excavation of station foundation pit in the study area is theoretically analyzed.Taking the seepage factor into account,the obtained data are analyzed and numerical simulation calculation is carried out with FLAC^3D,so as to analyze the stability of foundation pit.The distribution of pore water pressure,surface settlement,lateral deformation of retaining structure and axial force of internal support during foundation pit dewatering excavation are analyzed.By comparing with the actual detection situation,the above simulation results match with it,and the deformation of soil and retaining structure also meet the requirements.The numerical simulation results can accurately reflect the actual situation of the project.The main conclusions of this paper are as follows:（1）This paper summarizes the general situation of regional geological structure of Xuzhou Metro Line 1,analyzes the hydrogeological characteristics of Xuzhou Metro Line 1 and the calculation model of typical station foundation pit excavation precipitation.The engineering model analysis methods under different depth of water stop curtain,recharge well arrangement and different dewatering depth control methods are summarized.（2）Shizishan station has special hydrogeological conditions,the surrounding surface water and groundwater are widely distributed,and the groundwater supply is sufficient.This will cause a large amount of soil settlement,so it is necessary to take timely control measures to ensure the safety of construction and surrounding environment.（3）In the process of dewatering excavation of foundation pit,the pore water pressure changes most obviously near the center of foundation pit because of the groove distribution of pore water pressure,which tends to be stable with the passage of time.In the outside of the foundation pit,because of the existence of water stop curtain,the decrease of pore water pressure is not obvious.With the increase of the excavation depth,the surface settlement and its influence range gradually increase.The surface settlement presents a parabola distribution with the distance from the edge of the foundation pit,and the maximum surface settlement occurs at a little distance from the foundation pit.Dewatering and excavation affect the ground settlement together.Within a certain distance from the pit edge,the growth rate of settlement value gradually accelerates.When the distance exceeds a certain distance,the surface settlement begins to separate from the influence of foundation pit dewatering and excavation.The settlement decreases gradually with time,and the rate of reduction also decreases at the same time.Due to the instantaneous unloading caused by the excavation,the foundation pit heaves upward,and the most serious part of the bulge is on the central axis of the foundation pit.When the excavation depth of the foundation pit is deeper and deeper,the lateral deformation of the retaining structure of the foundation pit will increase first and then decrease.The internal supporting structure will produce more axial force at the location with larger deformation of the retaining structure.（4）The law of surface settlement under the measures of increasing the depth of water stop curtain,arranging recharge wells and increasing the depth of precipitation are obtained.With the increase of the depth of the waterproof curtain,the influence of the surface consolidation settlement is obviously reduced.In addition,increasing the depth of the waterproof curtain can effectively control the unloading uplift of the foundation pit bottom.However,the effect of water stop curtain beyond a certain depth on the surface settlement is no longer obvious.However,if the surface subsidence meets the control value,it should not be reinjected.Otherwise,the construction cost will be increased and the effect will be very small.The settlement of the ground surface is directly proportional to the dewatering depth of the foundation pit.The deeper the depth is,the greater the settlement is.Therefore,under the premise of ensuring safe construction in the actual precipitation process,the surface settlement value can be reduced by reducing the precipitation depth.