Estimation of pile bearing capacity in cohesionless soils using the simple pile load test technique

Abstract

Although numerous methods have been proposed to estimate pile bearing capacity, it is evident that pile load tests provide the most reliable prediction. However, pile load tests are not usually performed due to the time and money consuming process. To overcome such practical problems, the Simple Pile Load Test (SPLT) was developed. In spite of its simplicity in performing the test, the new technique has some shortcomings to be clarified for practical use. Two major concerns in this research are effects of load direction on shaft resistance and effects of pile tip size on end bearing capacity. In order to examine these points, both the field and the laboratory test were carried out. As a result, the new technique tends to underestimate the shaft resistance, but provides somewhat larger values of end bearing capacity. Many important factors have been disregarded in commonly available methods of pile bearing capacity prediction. Among the factors, actual soil condition near failure should not be neglected. It has been recognized that the angle of shearing resistance decreases as the applied stress increases, i.e., the failure envelope is not straight but curved. Considering high stress levels beneath the pile tip, the reduction in angle of shearing resistance may be substantial. Furthermore, most of the static formulae provide the bearing capacity factors that are very sensitive to the angle of shearing resistance. An example of consideration of stress levels is introduced. It was shown that the prediction based on the curved failure envelope is much closer to the measured capacity than the prediction which utilizes the initial angle of shearing resistance.