DETERMINATION OF Nϒ VALUES THROUGH MODEL TEST ON YAMUNA SAND AND BADARPUR SAND

Abstract

The most important geotechnical structures are the foundations, which transfer the load to the soil subgrade from the superstructures. The load carrying capacity of the soil per unit area is known as bearing capacity, based on which the foundation of structures is designed. There are mainly three factors on which present calculations of bearing capacity of a soil is based on. These are Nc, Nq and Nγ which depends on internal friction angle (φ) of soil. Various researchers reveal that the failure surface below footing for general shear failure is divided into rigid zone and shear zone. There are many conventional methods of study which reveal the predefined failure zone and failure slip surface for determination of failure load on the footing based on which the list of bearing capacity factors is given. The use of predefined failure zones and slip surfaces leads to conservative results for the determination of bearing capacity factors. To overcome this problem many researchers also tried iterative computational procedures based on limit equilibrium method, upper bound and lower bound method, method of characteristics incorporated with finite element methods. The analyses of bearing capacity factors based on these studies are convergent for the values of Nc and Nq, but in case of Nγ the results are divergent. None of this methods give exact solution for Nγ values. As a result, along with various methodologies Nγ values can be found with considerable differences whereas the values of Nc and Nq from different studies are very closely spaced. Table :1 shows the difference of Nγ values as per few well known equations.