Research On Numerical Simulation And Safety Monitoring Technology Of Deep Foundation Pit Engineering Under Complex Environmental Conditions

Based on the foundation pit excavation and support engineering of the research and development support base of China Academy of Aeronautics,this paper designs reasonable support schemes for different depth areas on the basis of analyzing the key and difficult points of deep foundation pit construction.At the same time,MIDAS /GTS finite element software is used to simulate the excavation process of the foundation pit.Based on the numerical simulation results,it provides guidance for the optimization of the support scheme and the formulation of the safety monitoring scheme of the foundation pit.Finally,through the safety monitoring of foundation pit construction,the safety of deep foundation pit excavation and support is evaluated.The main conclusions are as follows:(1)For the deep foundation pit engineering with large depth and span,rich groundwater conditions and complex surrounding environment,the method of "upper2.0m joint curtain pile + lower pile anchor" can be used for foundation pit support,and the method of "water stop curtain + relief well" can be used for groundwater treatment.According to the project of slope protection pile,soil wall protection between piles,curtain pile,anchor rod and decompression drainage well,the applicability of construction technology and technical requirements should be improved in combination with the engineering geological conditions.(2)Midas / GTS finite element software is used to simulate the excavation process of foundation pit,and the results of numerical analysis are explored in depth.The safety of the design scheme of foundation pit is analyzed from the perspectives of horizontaldisplacement of foundation pit soil,vertical settlement of surface,uplift of foundation pit bottom,etc.The influence scope of the horizontal displacement of the soil mass produced by the excavation of the foundation pit is the circular arc shape centered on the excavation area of the foundation pit.The maximum value of the horizontal displacement-16.16 mm occurs in the middle of the side wall of the foundation pit.During the design of the support scheme of the foundation pit,the support should be strengthened in this section,and the deformation of this position should be observed during the monitoring of the foundation pit.Due to the supporting effect of the foundation pit supporting structure,the vertical displacement of the ground along the side wall of the foundation pit is small on both sides and large in the middle,and the maximum vertical displacement of the ground is-29.58 mm at the mid span of the side wall of the foundation pit.The vertical displacement around the foundation pit increases first and then decreases,and reaches the maximum value at 10-20 m away from the foundation pit support pile.Due to the constraints of supporting structures such as supporting piles and anchor bolts around the foundation pit,the uplift value of soil at the bottom of the foundation pit gradually increases along the periphery to the center of the foundation pit in the shape of a ring,and the maximum uplift value of soil at the bottom of the pit is 33.12 mm in the center of the foundation pit.With the increase of the excavation depth,the restraint effect of the foundation pit supporting structure on the soil at the bottom of the foundation pit is gradually reduced.In the design of the foundation pit supporting scheme,the design of the lower supporting structure should be strengthened.(3)According to the design scheme of foundation pit and the results of numerical simulation analysis,a suitable safety monitoring scheme is proposed for the excavation and support engineering of foundation pit.Through the analysis of monitoring results of horizontal displacement,vertical displacement,deep horizontal displacement,internal force of pile body,anchor tension,settlement of surrounding buildings,settlement of surrounding road surface and settlement of surrounding land,the project risk can be found in time and emergency measures can be taken.At the same time,the finite element calculation results and safety monitoring results are compared and analyzed.The constitutive model and material parameters used in this paper can truly reflect theexcavation process of foundation pit,and provide reference for the scheme design and risk prediction of foundation pit excavation and support engineering.