Application Of Lower-bound Method In Bearing Capacity Of Soils

The bearing capacity of soils has been a core and basic problem of soil mechanics.At the same time,it is also the problem that all engineering constructors have to face and solve.At present,there are three main methods to calculate the ultimate bearing capacity of soils: limit equilibrium method,slip line method and limit analysis method.The limit equilibrium method is the most widely used in soil mechanics,three superposition formula of Terzaghi which is based on the limit equilibrium theory is also widely used,but the Terzaghi formula has a lot of assumptions,the error of the solution obtained and the exact solution is large;the slip line theory deals with the bearing capacity problem difficultly which is of complex boundary conditions.The advantage of limit analysis method in solving bearing capacity of soils is that the limit analysis method does not involve constitutive relation which is most difficultly to be understand in engineering,at the same time,the bearing capacity of complex boundary conditions can be solved,and obtain a very strict theoretical result.In this paper,based on the lower bound of limit analysis method,combined with the finite element method and linear programming method,the limit analysis method is programmed and the following conclusions are obtained:(1)The coefficient N? of bearing capacity of homogeneous foundation is solved,compared with the existing results,the calculation results are reasonable,and The bearing capacity coefficient N? of Sokolovskii is larger;in addition,the number of grids,the internal friction angle of the foundation,and the linear approximation of the yield criterion will affect the result of the lower bound solution..The effect of the foundation bearing capacity of the limit analysis finite element method such as overloading and the center load tilt,the error is well.(2)The bearing capacity is decreasing with the increase of the foundation width when the thickness of the crust is constant,and it finally reaches a stable value,which is linear with the thickness of the crust.(3)For two-layer soils,if the crust thickness is relatively small,The part of the upper soil is destroyed,and the general-shear failure will happen in the lower layer;when the thickness is relatively large,the failure occurs only in the crust layer and itwill be the general shear failure.This method can provide information in the engineering of two-layer layer soils.