Study On Deformation Characteristics Of Adjacent Super Deep Foundation Pit Excavation

With the development and utilization of underground space,more and more super deep foundation pit group projects appear in urban construction.Due to the mutual influence of excavation and construction of foundation pits,the deformation of retaining structure and its impact on the surrounding environment of adjacent foundation pits are more complex than that of single foundation pit.Therefore,it is of great significance to study the deformation characteristics of adjacent ultra deep foundation pit excavation for the scientific design and safe construction of foundation pit engineering.Based on the actual project of Hangzhou east station super deep foundation pit of Hangzhou metro line 6,through the model test and numerical simulation,this paper studies the deformation of retaining structure and surface settlement law of adjacent foundation pit excavation,and analyzes the relevant influencing factors.The main research contents and conclusions are as follows:(1)The indoor scale similar model tests of adjacent foundation pits under different excavation sequence and spacing were carried out to reveal the horizontal deformation and surface settlement of diaphragm wall.The test results show that:with the increase of the advanced excavation depth of the first excavation foundation pit,the deformation of the first excavation foundation pit far away from the side diaphragm wall and the next excavation foundation pit near the side diaphragm wall decreases,and the deformation of the first excavation foundation pit near the side diaphragm wall and the next excavation foundation pit far away from the side diaphragm wall increases;Due to the superposition effect,the ground settlement around the foundation pit is greater under the synchronous excavation;With the increase of foundation pit spacing,the horizontal deformation of diaphragm wall far away from the adjacent foundation pit decreases,while the horizontal deformation of diaphragm wall near the adjacent side increases.(2)The accuracy of the constitutive model and the rationality of the numerical model are verified by the monitoring data.The deformation of retaining structure and ground settlement in the process of foundation pit excavation are studied,and the influence of different excavation sequence and spacing on adjacent foundation pit excavation deformation is further analyzed.The numerical simulation results show that MMC model can better reflect the actual engineering deformation than MC model;The overall deformation of diaphragm wall near two adjacent foundation pits is obviously different,and the surface settlement between pits is smaller than that outside pits;With the increase of the advanced excavation depth of the first excavation foundation pit,the deformation of the diaphragm wall near the first excavation foundation pit increases,and then the diaphragm wall near the second excavation foundation pit gradually moves to the first excavation foundation pit;When the advanced excavation depth is greater than 0.62 H_e(H_e is the excavation depth of foundation pit),the maximum deformation of diaphragm wall is basically unchanged;The influence range of adjacent foundation pit excavation is about 2.5 H_e.The influence of excavation sequence on the deformation of adjacent diaphragm wall is consistent under different spacing,and the deformation of adjacent diaphragm wall increases with the increase of spacing;With the increase of spacing,the surface settlement of soil between pits first increases and then decreases,and the maximum settlement value is at 1.5 H_e spacing.(3)Taking the horizontal deformation and surface settlement of diaphragm wall as evaluation indexes,the orthogonal experiment was carried out by numerical simulation to study the influence of foundation pit spacing,diaphragm wall stiffness,insertion ratio,advanced excavation depth,reinforcement depth of passive zone and reinforcement thickness of soft soil between pits on the horizontal deformation and surface settlement of diaphragm wall.The results show that the reinforcement depth of passive zone,the distance between foundation pits and the insertion ratio of diaphragm wall have great influence on the design.