Stability Analysis Of Double-row Pile Supporting Structure For Deep Foundation Pit In Soft Soil With High Water Level

The double-row pile retaining structure has the advantages of good overall stability,large lateral stiffness and low cost.It has been widely used in deep foundation pit engineering.However,it has poor guiding effect on the supporting mechanism and safety and stability of deep foundation pit in different engineering practice.Based on a deep foundation pit project of a pumping station in Wuhan,combined with field monitoring and three-dimensional finite element numerical simulation,the stability of double-row piles supporting structure of deep foundation pit is comprehensively analyzed,and a series of valuable results are obtained.The main research contents are as follows:(1)The stress mechanism and deformation of double-row piles in deep foundation pit engineering are studied.The whole construction process is monitored and the data are investigated in practice.The causes and status quo of the accidents such as cracks,piping and collapse are analyzed by combining various displacement curves.The special geological conditions of the deep foundation pit subjected to soft soil interlayer,the unrestricted construction design process and the strength drop are obtained.The influence of external conditions such as rain piping will bring about different changes that endanger its stability.(2)Using MIDAS GTS NX three-dimensional finite element analysis software,the stress numerical simulation of double-row piles and the coupling numerical simulation model of dewatering stress and seepage of equivalent diaphragm wall foundation pit are done respectively,and the curves of deep horizontal displacement,surface settlement,crown-beam vertical displacement and seepage pore pressure of double-row piles supporting structure under different simulated conditions under different construction conditions are drawn.The deformation difference of row piles is summarized and analyzed.It is concluded that the strain curves of measured and simulated values are roughly consistent,but there are some gaps in some parts,which verifies the rationality of numerical simulation.(3)Sensitivity analysis is made on the factors affecting the stability of double-row piles in deep foundation pit,and three main factors are determined as cohesion,internal friction angle and elastic modulus of double-row piles.MIDAS finite element software is used to model and simulate the variation of parameters at(±)8%,(±)15%,(±)30%.Taking the maximum lateral horizontal displacement as the evaluation index,the average sensitivity coefficients of uncertain factors are calculated.The elastic modulus of double-row piles is the most sensitive factor,followed by cohesion,and finally the internal friction angle.