Research On Appraisal Of The Safety Criteria And Calculation Of The Ultimate Bearing Capacity Of Foundation

In recent years,with the rapid development of Chinese infrastructure,such as roads railways airports ports and docks, the research on the ultimate bearing capacity of foundation is increasing. The existing methods for calculating the Ultimate bearing capacity of foundation are mainly semi-empirical formulas which are only available for Homogeneous soil foundation. In fact, studies on the calculation of the ultimate bearing capacity of layered foundation which is a common kind of ground soil in constructions are not matuare and perfect, have not yet formed a complete theoretical system.In order to solve the problem that there is no an accurate method for the calculation of the ultimate bearing capacity of layered foundation, main work and study of this article are as follow:(1) A numerical simulation method to the calculation of the ultimale bearing capacity of layered foundation is proposed based, on Upper-bound Approach.(2 )This paper introduces the simplex method and integrates the random search method to find the critical sliding surface, obtain the minimum loading factor and calculate the ultimate bearing capacity.(3) The calculation program, by VBA language embedded in EXCEL, for ultimate bearing capacity of foundation is worked out, is worked out to find the Solution of complex frunction and realize in calculating those complicated computations automatically.(4)It is proved that the method and program are accurate by comparing with the field test,The comparison between the calculated results and the experimental ones shows that: for the homogeneous soil, the error between Vesic method and this method is the smallest, the error is less than 1%, and the error between Meyerhof and upper bound solution is larger than 20%.For the layered soil, the upper bound solution is close to the experimental results. Compared with the upper bound solution, the results of Hansen’s method are quite different.Using risk analysis of engineering structure and reliability design method, this paper investigates choosing Value Standards of the safety factor for stability analysis of foundation based on Strength safety factor method. The results show that the allowable safety factor of foundation (1.35) is slightly larger than corresponding values of Slope and other similar buildings. The author applied the theory of reliability analysis on a target example andobtained the calibrated partial factors, being close to the overseas specifications. The calibrated partial factors are further validated by the ’Ratio of safety margin’ theory proposed by the authors’research team.