Analysis On Deformation Behavior Of The Subway Foundation Pit In Cobble Stratum In Chengdu Area

In recent years,with the construction of a large number of subway,subway foundation pit construction projects continue to emerge,but due to the special nature of subway foundation pit engineering,its deformation has a strict requirement.In the soft soil area,the research on the deformation of the foundation pit is rich,but for the foundation pit in cobble stratum in Chengdu area,the research on the deformation of the foundation pit is too less to know its deformation law.In this paper,based on the foundation pit engineering of Chengdu subway station,this paper makes a deep research on the deformation law of excavation construction process by means of the combination of field pit site monitoring and three-dimensional numerical simulation.The following work is carried out specifically:(1)The field monitoring data of the foundation pit are analyzed and summarized,and the deformation law of the retaining structure and the characteristics of the earth's settlement behind the wall are obtained briefly.(2)MIDAS-GTS finite element software is used to simulate the process of foundation pit of the subway station,the deformation of the retaining structure,the settlement of the pit and the deformation of the bottom of the pit are analyzed.The size and distribution of the back earth pressure in the envelope are studied.(3)The factors influencing the deformation of the foundation pit are analyzed and discussed.On this basis,the calculation method of the settlement of the soil is put forward according to the principle of the soil loss theory.Through the work above,this paper draws the following conclusions:(1)The maximum horizontal displacement of the retaining structure is 10mm(0.6 ‰H),and it appears near the middle of the foundation pit enclosure structure(0.48?0.54H);the influence of the settlement of the soil outside the pit is about 1.5H,and the main influence area is 0?0.7H;the maximum earth's settlement behind the wall is 0.67‰H,and the maximum settlement appears near 0.25H.(2)When the excavation is completed,the soil pressure acting on the supporting piles over the excavation face is 0.5?0.7 times of the Rankine's earth pressure.(3)The deformation of the pile body to the soil parameter sensitivity degree from large to small order is:internal friction angle,Poisson ratio,soil modulus and cohesion.(4)In the design of Chengdu subway pit,it is suggested that the stratigraphic parameters of Chengdu will be taken as follows:the cohesive force of the small pebbles and the dense pebbles should be taken from 0 to 5kPa and the cohesive force of the pebble is 5 to 10kPa.And the retaining structure pile diameter is about 1.2m;support arrangement using under the secret form.(5)The insertion ratio of the pile is proportional to the influence of the settlement of the soil outside the pit.The maximum sedimentation value of the soil is 1.1 times the maximum displacement value of the pile.