Numerical Analysis And Deformation Prediction Of Deep Foundation Pit Based On Modified Moorcoulomb Model

In order to deeply study the deformation characteristics of deep foundation pit support,based on the deep foundation pit project of "Tianren mansion" in Zhangjiakou,Hebei Province,triaxial shear test,unloading reloading test and consolidation test of soil samples from different geological layers of deep foundation pit under different range of confining pressure were carried out,and modified Mohr Coulomb modulus such as secant modulus and unloading elastic modulus were obtained from the curve of stress-strain relationship By introducing the finite element parameters into MIDAS GTS/NX,the finite element analysis method is used to analyze the different characteristics of Mohr Coulomb model and modified Mohr Coulomb model in the simulation of deep foundation pit row pile support deformation and surface settlement.Through the comparison with the actual monitoring data,the applicability of modified Mohr Coulomb model in the simulation of deep foundation pit row pile support deformation is obtained..In order to further explore the influence of parameters of modified Mohr-Coulomb model on the sensitivity of simulated deep foundation pit deformation,these parameters were increased or decreased in proportion,and the sensitivity of each parameter to foundation pit deformation was studied.Finally,neural network was used to connect the parameters with foundation pit deformation,and the following conclusions were obtained:(1)In the process of experimental study,it is found that the silt in the test sample is softening failure under different confining pressures.Under the larger confining pressure,the effective deviatoric stress-strain curve of fine sand has no peak point,showing hardening failure.(2)Before the failure of the soil,the unloading and reloading have little effect on the stress-strain curve of the soil,and the unloading and reloading modulus before and after the peak point of deviatoric stress is almost the same.The tangent modulus,secant modulus and compression modulus of the tested silt are approximately equal.With the increase of the reference stress,the ratio of unloading modulus to compression modulus increases in quadratic function.The accuracy of the parameters is verified by numerical simulation,so the experimental research is an important way of parameter accuracy.(3)In the prediction of surface settlement and horizontal displacement of pile row,the settlement value predicted by the Mohr Coulomb model differs greatly from the measured value.The predicted values of modified Mohr Coulomb model under different reference stresses are in good agreement with the measured displacement curves.Therefore,it is of more reference value to use the modified Molcoulon constitutive model under different reference stresses to predict the deformation of foundation pit excavation.(4)Among the five parameters,the internal friction Angle has a great influence on the deformation of foundation pit,with the highest sensitivity,the lowest sensitivity of tangent modulus,and the moderate and similar sensitivity of cohesive force,secant modulus and unloading elastic modulus.(5)By establishing the neural network relationship between soil parameter values and foundation pit deformation values,an algorithm that can predict foundation pit deformation for similar foundation pit projects is obtained,which has a good effect on promoting foundation pit deformation prediction.