Analysis Of The Impact Of Deep Foundation Pit Excavation On Adjacent Existing Stations

With the development of the city,the large-scale construction of the subway has led to the rise of buildings along the subway.The impact of the construction of the foundation pit adjacent to the subway station on the station cannot be ignored,especially for the already operating subway.The difference of the internal and external earth pressure generated during the excavation and re-building process of the foundation pit may easily lead to uneven deformation of the structures of the adjacent subway stations in the vertical and horizontal directions,thereby adversely affecting the structure of the subway station.On the other hand,the excavation of the foundation pit changed the balance of the original soil stress field.As the depth of excavation increases,the basal soil after the unloading occurs bulging rebound,and the lateral force and deformation of the foundation pit supporting structure increase.Even the safety of the subway station structure is endangered.For this reason,this paper takes a foundation pit project in Kunming as the background.Both the north and south sides of the project are the A pit and the B pit,and there are tunnels and stations running through the pits.According to the engineering survey,a single foundation pit excavation model and a group pit excavation model were established by comprehensively using field surveys,engineering analogy analysis,numerical simulation and monitoring and comparative analysis.Scheme 1: Set up a single foundation pit excavation model,excavate A and B foundation pits respectively to the bottom of the pit,analyze the effect of single foundation pit excavation on the deformation of the station and the foundation pit itself;Scheme 2: According to the actual project,establish A,B.The overall model of the pit,tunnel and station will analyze the three excavation sequences of the foundation pit in the case of group pits((1)A and B excavation at the same time to the bottom of the pit;(2)Excavation of the A pit to the pit bottom,and then open Excavate B foundation pit;(3)excavate B foundation pit to pit bottom,excavate A foundation pit again)Impact on subway station and pit itself,at the same time,preliminary superposition effect of deformation of subway station caused by excavation ofadjacent pits Discuss and analyze.The main results and conclusions are as follows:(1)Comparing the calculated values and measured values of the maximum vertical displacement of the subway station during the excavation of the foundation pit,the results confirm the feasibility and correctness of the numerical simulation scheme.Both sides of the pit itself as a whole safety and stability factor,the maximum displacement deformation,the amount of surface settlement to meet the specification requirements.Therefore,the comprehensive judgment of the pit excavation support form and parameter selection is safe and reasonable,and it can meet the engineering requirements;(2)When excavating a single foundation pit,the impact on the station is small.As the excavation depth of the foundation pit increases,the impact on the station is greater,and the displacement changes at the entrance and exit of the station is the greatest.The impact of the excavation of the foundation pit B on the station is more significant than that of the A foundation pit.At the same time,the excavation of the foundation pit will cause some disturbance to the stratum.When the stratum depth is3 times the excavation depth of the foundation pit,the stratum will be settled.When the stratum depth is 4 times the excavation depth of the foundation pit,the excavation of the foundation pit is almost the same as that of the strata.No effect.The value of ground settlement near the midpoint of the long side of the foundation pit is larger,the value of ground settlement near the midpoint of the short side of the foundation pit is smaller,and the value of ground settlement near the corner of the foundation pit is the smallest;(3)For the protection of the station structure,the three excavation conditions have little effect on the horizontal displacement of the station when the group of pits are excavated,and the vertical deformation is the main influence on the station.The change in vertical displacement of the station at the middle of the working condition is the minimum so the condition is the optimal excavation plan.On the other hand,the group pit excavation has a greater impact on the deformation of the foundation pit,and the larger the area of the foundation pit,the greater the impact.The three vertical displacements of the B foundation pit are greater than that of the A foundation pit,and the foundation pit level The impact of displacement is minimal,but the horizontal displacement of the foundation pit is greater than the horizontal displacement of asingle foundation pit due to the group pit effect;(4)The superposition of ground settlement caused by excavation of adjacent foundation pits,the ground subsidence when the two foundation pits are excavated simultaneously is greater than the ground subsidence during excavation of a single foundation pit,and there is a certain nonlinear superposition effect on the ground displacement.However,the difference in ground settlement at the bottom of the foundation pit under different conditions is not significant.