Parameters Research Of Column In Subway Station Excavated By Semi Top-Down Method With Soft Soil Area

In recent years, with the rapid development of urban infrastructure, urban rail transit construction is booming. So more and more excavation projects which is becoming larger and deeper emerge. Various construction engineering methods are gradually rising and mature. The complexity of environment and the difficulty of construction conditions also cause many new problems. The thesis, taking the deep pit of Guangji Road subway station in Suzhou as the background and using theoretical calculations and finite element simulation method, studies the uplift deformation of column in the semi-cover excavation pit. The main content is as follows:(1) The verifying method of the structural design of latticed column in the semi-cover excavation with the use of the vertical bracing system is summarized. As to the differential settlement caused by the column uplift when the foundation ditch is excavated, the inversion formula on the allowed value in vertical settlement can be deduced through the calculation of the concrete support’s ultimate bending moment.(2) With regard to the problem of the foundation ditch with variable width, the mechanism of the uplift caused by the excavation is firstly analyzed. And then the computing model is established using the finite element software. And the software MIDAS/GTS can help to deal with the change rule among the ditch’s width, the value of uplift at the bottom and the width of the temporary pavement plate. And these conclusions can be drew as fellows:the formation of the uplift is variable when the ratio of the width to depth varies:when the deformation at the bottom is plastic and the bilateral "double peak" is3or4meter away from the continuous concrete wall, the effect of excavation on columns can be well simulated by the software.(3) A three-dimensional finite element model is established, based on the realistic engineering project of the foundation. According to the numerical simulation results. the deformation law of the temporary pavement slab under different conditions is analyzed. Through the comparison of the measured and calculated values. the rationality and applicability of the paper is verified. On this basis. the effect of the length, diameter and spacing of piles on the temporary pavement slab is analyzed by changing the pile parameters, thus drawing a conclusion that pile length and pile spacing have greater effect on the uplift of the column pile.(4) At last, taking deep pit of Guangji Road subway station in Suzhou as the background, this thesis analyses the deformation of semi top-down method, such as the deformation of the continuous concrete wall, the uplift and subsidence of the temporary pavement slab, the surface subsidence etc.