Experimental and analytical investigations on skin friction and end bearing resistance of single pile

Abstract

ABSTRACT

In this thesis work, an analytical method is established to separate skin frictional resistance and end bearing components for a given load on a pile. The method is based on static load-settlement data and direct shear test data. Three numbers of model piles of diameter 50 mm, 75 mm and 100 mm, each of length 1000 mm, are used for laboratory model tests. Each pile is cast in a hole made in a clay soil layer. This is done to get rough surface of the piles. A wooden box is used to prepare model ground in the laboratory. The box is 915 mm x 915 mm in cross section and 1676 mm in height. A reaction frame (consisting of box section, C-channel and rod) is made to apply load to the test pile using a hydraulic jack. A load cell arrangement with display monitor is made to measure the pile end resistance directly when a static load is applied on a model pile. To get pile end force, two springs (one with low stiffness and the other with relatively high stiffness) are used in the tests. The spring is placed just below the pile and rested on top of the load cell. Also tests are performed without spring beneath the pile bottom in which case the pile rested on sand. Pile end bearing and settlement are recorded when spring is used and these end bearing and settlement are used as reference to separate end bearing and skin frictional resistance when spring is not used. The proposed analytical method is based on the mobilized friction angle. For any given displacement the mobilized friction angle is obtained from a polynomial equation fitted to the τ/σ vs ε curve as obtained in a direct shear test. The results of analytical method are compared with those obtained from model tests. The end bearing for 50 mm, 75 mm and 100 mm diameter piles obtained in model are found to be respectively 34%, 42% and 28% higher than the end bearing obtained by the analytical method. However, the skin resistance from analytical method for 50 mm, 75 mm and 100 mm diameter piles are found to be respectively 29%, 33% and 28% larger than the model test values.