Axisymmetric problems on capacity and passive earth pressures in soils with bilinear ground surface by the method of characteristics.

Abstract

Shallow footings are placed on different types of soil under different site conditions. A shallow footing placed in a depression with stratified soil is a good example of a practical problem. For a realistic analysis of the bearing capacity, these factors should be taken into account. After presenting the scope and nature of the work undertaken in Chapter 1, the available literature on the bearing capacity of footings and earth pressures on retaining walls is reviewed in Chapter 2. Using the method of characteristics, bearing capacity of circular footings and passive earth pressures on axisymmetric retaining structures are analysed in Chapters 3 through 6. In Chapter 3, the bearing capacity of a shallow circular footing placed adjacent to a slope having a positive gradient around the footing is studied. The soil is homogeneous and isotropic and has both cohesion and angle of internal friction. Numerical results are presented in the form of non dimensional bearing capacity factors NNN and N qN_{\gamma q}N q for various values of angle of internal friction, inclination of adjacent slope, wall friction, and depth of footing. Results show that the adjacent slope and the depth of footing have substantial influence on bearing capacity factors. The problems of passive earth pressures on cylindrical and truncated conical retaining structures in soils with bilinear free surfaces are analysed in Chapter 4. Numerical results are presented in the form of non dimensional passive earth pressure coefficients KKK and Kp.cyK_{p.cy}Kp.cy . Results show that passive earth pressure on axisymmetric retaining structures increases with increase in wall friction and inclination of the sides. The analysis of passive earth pressures on truncated conical retaining structures is extended for determining passive earth pressures on axisymmetric circular, elliptical, and parabolic curved retaining structures in Chapter 5. Results show that passive earth pressures on curved retaining structures increase with increase in curvature of the structure. In Chapter 6, the bearing capacity of a shallow circular footing placed at the interface of a two layered soil (top soil weaker than bottom soil) is analysed. The footing is placed adjacent to a slope having a positive gradient. Numerical results show that the bearing capacity of the footing depends on the strengths of the two soil layers, apart from the influences of footing depth and inclination of the slope. Finally, in Chapter 7, the usefulness of the results presented is discussed and important conclusions of the present investigations are summarised.