Research On The Monitor And Numerical Simulation Of Deformation For Deep Foundation Pit In A Harbin Subway Station

The urban rail transit facilities represented by subway can fundamentally solve the problem of urban traffic congestion and promote regional economic development.Therefore,the subway in every city is flourishing,and it is developing in the direction of "greater" and "deeper".However,land subsidence,foundation pit instability and building tilt,which are caused by the deformation of deep foundation pit in subway station have been the key issues in the subway construction.It is of great value and significance to study the deformation rules of deep foundation pit of subway station.Based on the deep foundation pit of the Xiangjiang Road Station of the II phase of Harbin Metro Line 3,the paper applies the in-situ monitoring and numerical simulation to study the rules of the ground settlement,the horizontal displacement of the pile,the supporting axis force and the horizontal displacement at the top of the pile.According to the characteristics of the deformation,the deformation mechanism is analyzed,and the deformation control measures for deep foundation pit at Xiangjiang Road Station are put forward.The main conclusions are listed:(1)After the completion of foundation pit excavation,the soil deformation around the foundation pit is generally groove-shaped.The cumulative maximum value of the ground settlement is not at the edge of the foundation pit,but is 5 meters away from the edge of the foundation pit.The maximum value is 19.46 mm.(2)The excavation depth of the foundation pit is relatively shallow in the early stage,and the deformation shape of the retaining pile is a forward-inclined type in the foundation pit.The excavation depth of the foundation pit increases,so that the deformation pattern of the forward dip changes into the bow shape.The maximum value of the horizontal displacement of the pile gradually moves downward from the top of the retaining pile.(3)There is a close relationship between the change of the supporting axial force and the horizontal displacement of the pile.When piles in cantilever state,the axial force of the first steel supporting shaft increases significantly.When the deformation of the retaining pile is changed from cantilever to parabolic shape,the axial force of the second steel supporting shaft located in the middle of the pit is obviously greater than other steel supports.(4)In the course of construction,the retaining piles gradually incline into the foundation pit as the excavation depth of the foundation pit increases,and the horizontal displacement at the top of the pile also increases.After the foundation pit excavation is completed,the force of the retaining pile is balanced,and the rate of change of the horizontal displacement at the top of pile decreases.At this time,the maximum horizontal displacement of the ZDS-2 monitoring point is 2.67 mm.(5)By comparing the simulated data with the measured data,it is found that the deformation data of the envelope structure and soil obtained by using the finite element method to simulate the excavation of the foundation pit are close to the in-situ monitoring data,and the deformation rules are basically identical.It shows that using this finite element model can better predict the deformation during the construction of deep foundation pits.(6)The deformation rules of deep foundation pit of Xiangjiang Road Station from the level of deformation mechanism can be summarized as the horizontal displacement of the retaining structure,plastic uplifts and the surface subsidence that occurred as a block performance,shrinkage performance,the soil arch effect.