Numerical Simulation Study On Uplift Performance Of Digged Foundations In Unsaturated-saturated Soil

Due to economic,environmental protection and good uplift bearing capacity,the digged foundation is widely used in transmission lines,underground spaces and buildings and other projects.The rainfall infiltration caused soil to change from unsaturated state to saturated state,so that the soil matrix suction was reduced,which leaded to the decrease of soil shear strength,and ultimately the weakening of the bearing capacity of the foundation in the soil.Under the condition of rainfall infiltration,it is very important to study the uplift bearing capacity of the digged foundation in unsaturated –saturated soil.Under the natural conditions,the in-situ tests of the uplift bearing capacity of the digged foundations were carried out in the unsaturated silty clay field without non-rainfall,and the soil tests were carried out,which included density,water content,specific gravity,consolidation,direct shear tests,so that determined the soil parameters of the numerical simulation of the basic bearing capacity and provided the basis for validating the rationality of the model and parameters.Based on the uniformly effective stress equation and uniformly shear strength formula of unsaturated-saturated soil,the suction component was introduced.Based on the SWCC curve,in the condition of seepage,the VG-M permeability coefficient function was used to establish the numerical calculation model for studying the uplift bearing capacity of the digged foundation.Comparing the simulation results with the results of in situ tests,it was found that the two fitting degrees were high,which verified that the numerical calculation model and parameters were reasonable.The numerical simulations of the uplift bearing capacity of the digged foundation under different rainfall time conditions were carried out by using FISH language.The laws of the uplift bearing capacity of foundations,soil suction,saturation and development of plastic damage zone were analyzed.The concept of the reduction coefficient of the uplift ultimate bearing capacity was put forward,and under the geological condition of the research site,the formula of reduction coefficient was summarized,and the formula was used to predict the uplift ultimate bearing capacity of foundation,also the results were good,so it can provide the theoretical support for predicting the uplift bearing capacity of foundation,and methods for the study of foundation stability.