Analysis Of The Influence Of Deep Foundation Pit Excavation On Surrounding Buildings

With the rapid development of national economy and urban construction,the number and scale of deep foundation pit engineering in metro station are also increasing,and the environmental protection around the foundation pit is becoming more and more prominent.The research on the influence of deformation of surrounding buildings caused by deep foundation pit excavation is of great significance to continue to improve the design of retaining structure of deep foundation pit and reduce engineering accidents.Based on the deep foundation pit engineering of a metro in a city,this paper studies the influence of foundation pit excavation on the deformation of surrounding buildings(building location,foundation depth,foundation stiffness)and the influencing factors(stiffness,width,depth,reinforcement position)of foundation pit reinforcement.The main research work and achievements are as follows:(1)On the basis of the research on the interaction between deep foundation pit and surrounding buildings and the theory of building deformation caused by deep foundation pit excavation by scholars at home and abroad,the field measurement and statistical analysis of several deep foundation pit engineering cases in soft soil area are carried out,and the distribution law and influencing factors of settlement of deep foundation and shallow foundation buildings in soft soil area are obtained.The results show that: the average settlement of deep foundation buildings is0.6‰H,the average settlement of shallow foundation buildings is 1‰H,and the average settlement of shallow foundation buildings is 1.7 times of the average settlement of deep foundation buildings;the differential settlement mostly distributes between 0 and 5 millimeter,and the average lateral relative settlement is1.8 times of the average longitudinal relative settlement.(2)The numerical calculation model of interaction between deep foundation pit and surrounding buildings is established.The simulation results show that when the longitudinal walls of buildings and the long sides of foundation pits are parallel,when the longitudinal walls of buildings and the long sides of foundation pits are perpendicular,the excavation of subway foundation pits has less influence on the maximum settlement of the surface around the pits,and has greater influence on the maximum settlement of the foundation of buildings and on the differential settlement of surrounding buildings.Increasing the stiffness(or depth)of the building foundation can improve the uneven settlement of the building;increasing the depth of the building foundation has little significance in reducing the maximum settlement value of the building foundation.(3)The influence of the stiffness,width,depth and position of reinforcement body on the settlement of building foundation is studied.The results show that the reinforcement of pit bottom can effectively control the settlement of building and the ground settlement around the building;the full hall reinforcement can reduce the differential settlement of building foundation more effectively than the strip reinforcement;the width of strip reinforcement body exists between 0.5b and b(b is the width of foundation pit).The maximum settlement of building foundation decreases with the increase of the stiffness(or depth)of the reinforcement body,but when the stiffness(or depth)of the reinforcement body reaches a certain value,the effect of the increase of the stiffness(or depth)of the reinforcement body on reducing the variation of the maximum settlement of building foundation is not obvious.Fixed conditions,the best reinforcement effect is from the excavation face of the bottom of the pit.(4)It is proposed that the settlement control values of surrounding deep foundation buildings and shallow foundation buildings are 20 mm and 35 mm respectively for metro foundation pits excavated in soft soil areas with a depth of15~18m.