Investigation on Uplift Capacity of Shallow Foundations on Cohesionless Soil

Abstract

Shallow foundations are commonly used in Sri Lanka for communication towers, power transmission towers and towers for wind turbines. The design of these foundations is based on several assumptions and therefore, a large factor of safety is imposed on estimated ultimate uplift capacity. In view of the above, the uplift capacity of shallow foundations on dry sand was determined in the present research by conducting laboratory model tests on circular and square foundation models. The results were compared with the uplift capacities obtained from analytical solutions for both circular and square flat foundations. Two foundation models (circular and square) at three different depths in dry sand were tested and the uplift force and upward displacement of each model were investigated. Uplift force versus upward displacement characteristics obtained from experimental analysis was compared with the uplift capacity obtained from analytical solutions. From both experimental and theoretical results, it can be concluded that the uplifting capacity of square foundation is higher than circular foundation at each depth. Also the uplifting capacity is increased with embedded depth of foundation for both types of foundations. Another important conclusion is that, the angle between the vertical plane and the failure plane is nearly half of the friction angle of the soil.