Numerical Analysis On Ultimate Bearing Capacity Of Several Common Kinds Of Nonhomogeneous Foundations

Soft ground is widely distributed in our country,especially in the coastal area which is accounting for the proportion of gross domestic product(GDP)in China up to 60%.With the rapid development of national economy in our country in recent years,a large number of ultra-high,over-limit buildings and facilities such as high-speed railway are under rapid construction,and requirements on bearing capacity and deformation of these foundations is higher.While foundation treatment is needed in most of the situations,filled foundation and composite foundation are widely adopted for foundation treatments.Generally speaking,a deeper understanding of the ultimate bearing capacity and failure mechanism of these kinds of foundation is requiredThree-dimensional numerical analysis model is established by using the finite difference method to analyze the ultimate bearing capacity and failure mechanism of cohesive nonhomogeneous foundation under rectangular and circular footings.Analysis results show that with the increase of the uneven coefficient of the strength of cohesive soil,the ultimate bearing capacity increases.The roughness of base affects the bearing capacity coefficient.Shape factors of rectangular and circular footings decrease when increasing the uneven coefficient of the strength of cohesive soil.The numerical results for the rectangular footing when the footing’s length is 10 times as its width and those for strip footing are equal.A finite difference method was used here to analyze the influence parameters on the depth modification factor,and the results is compared with the value suggested by the code.The analysis results show that failure mechanisms have paramount influence on ultimate bearing capacity which increases with the width and depth of filling area,level of surcharge,and the internal friction angle of soil.Generally,the recommended value is conservative in most cases.The recommended value is likely to be unsafe when the strength of weak soillayers is weak while the filling depth is large.A finite difference method was used to analyze the influence parameters on the bearing capacity of cement mixing pile composite foundation.The analysis results show that the bearing capacity factor Nγ of single pile composite foundation increases with the increase of pile length and replacement ratio.The failure mode of composite foundation is general failure mode while pile length is short.And the failure mode of composite foundation is punching shear mode while pile length is long.With the pile length and the strength of reinforced area increasing and the replacement ratio decreasing the failure mode turns into local failure mode.As the integrity of reinforced area in multi-pile composite foundation is stronger,the transformation process is harder.