Study Of Ultimate Bearing Capacity Calculation Using Meyerhof & Hanna Theory

It is often the case in Foundation Engineering that foundation subsoils are consisted of more than one layer. Up to now, Hansen's method and Meyerof's method for two-layer subsoils are the general two options for estimating the bearing capacity. But the methods can only treat some simple cases, which can not deal with muti-layer subsoils. Therefore the mechanism of failure and the methods of estimating the ultimate bearing capacity should be further studied for inhomogeneous medium. In this paper, in-site test, plastic FEM were performed to study the problem.The research stratagem and conclusions can be summarized as follow :Information concerning with the bearing capacity of footings on inhomogeneous medium was collected and evaluated. In general , the determination of the failure mechanism for the inhomogeneous subsoil plays an important role in predicting the ultimate bearing capacity.A finite element program is compiled to search for the failure mechanism of the inhomogeneous subsoil.For the bearing capacity of layered foundations calculated by Meyerhof and Hanna formula, its calculation procedure is refined; the common bearing capacity model is deduced. The bearing capacity of layered foundation calculated by Meyerhof and Hanna formula is validated by using the results of in-situ load experimentation so as to modify the formula. (1) The key step of the formula is to determine the failureplane limit depth, which significantly influenced the result. (2) By the large-scale stress plane in-situ examination, as the layers of soil exceed double, the ultimate bearing capacity of layered foundation calculated by Meyerhof and Hanna formula are compared well.(3)Based on plastic model,a finite element program PLAXIS is compiled to search for the failure mechanism of the inhomogeneous subsoil.Some in—situ loading tests are performed in Tianjin New Harbor area and the experimental data are compared with the computational results of the finite element methods.The reliability of the finite element program is verified by the comparison.By simulating the development of interior strain,deformation and the failure face of the inhomogeneous subsoil under outer load ,the failure-mechanism of the foundation of this kind is deduced.By virtue of numerical analyses,it has been found that under the ultimate load the inhomogeneous subsoil exhibits the characteristics of general shear failure or local shear failure.The plastic strains firstly appear on the edge of the footings.With increasing of the load,the plastic zone expands and joints together at last.The appea ring of the continuous plastic zone means that bearing capacity failure occurs in the subsoil,and the bearing capacity of the foundation has reached to its ultimate value.Some conclusions of the paper can be used in the revisal of the Code for the Foundation of Harbor Engineering (JTJ250)...