The Reliability Analysis Of Strip Footing On The Unsaturated Soil

To study the stability of foundation in unsaturated soil, random variables method and random field method is used for reliability analysis and sensitivity analysis of the strip foundation. The main research contents are as follows:Random variable method.put the unsaturated soil mechanics parameters (cohesion c, internal friction Angle φ) and the hydraulic parameters (fitting parameters a, n, and the saturated moisture content θs and the residual moisture content θr) as random variables, respectively, using the theoretical formula method and numerical simulation method to calculate the ultimate bearing capacity of strip foundation in unsaturated soil, on this basis of foundation bearing capacity limit state for reliability calculation and sensitivity analysis of parameters.The results showed that:The descending order to the sensitivity of reliability index β is φ、c、a、n、θs and θr during their six basic random variables. Besides, the effects of θs and θr on reliability index β almost can be ignored.The reliability index β increase with the increase of c、φ、 a and θr, and decrease with the increase of n and θs. When considering the rainfall infiltration in unsaturated soil, the reliability index β of the strip foundation increase with the increase of the safety factor Fs, initial suction yφ0 and allow the settlemen Sa, but decrease with the increase of rainfall intensity.Random field method:in order to consider the spatial variation of parameters of soils is in vestigated, sensitivity analysis on the basis of the random variable method, depending on the unsaturated soil mechanics parameters (cohesion c, internal friction Angle φ) for the random field, the Karhunen-Loeve series expansion method is used for discrete random field,the work mainly concentrated on discrete method of random field and it’s discretization error and basic variable’s effects on average ultimate bearing capacity. The results showed that: truncation terms decrease with the increase of horizontal correlation distance and decrease with the increase of vertical correlation distance when the horizontal correlation distance is same.To truncation terms, vertical correlation distance is more sensitive than horizontal correlation distance. The average of ultimate bearing capacity increases with the increase of initial suction. And a large initial suction corresponds to a relatively small variation coefficient of ultimate bearing capacity.In short, this paper provides reference for numerical simulation of the ultimate bearing capacity and reliability analysis of foundation.