A thesis submitted in partial fulfilment of the requirements for the degree of Master of Engineering

Thesis (M.Eng.) - Asian Institute of Technology, 1991

The soil failure patterns and corresponding soil reactions under the action of flat vertical tools operating at quasi-static conditions in dry compact sand were studied. The soil failure was found to be by progressive shear, starting horizontally from the tool tip up to a certain distance and then progressing upward towards horizontal soil surface. The shear angle was found to be 27° ± 2°, which was very close to the theoretical angle (s/4-Z/2 ) of 26.5°, for all the tools studied. With increase in tool depth, even at the same aspect ratio, the additional shearing within already failed zones of soil became more and more prominent. At depths of 5 and 7.5 cm, the failure patterns remained almost the same with a change in aspect ratio, whereas at higher depths of 10 and 12.5 cm the failure patterns were found to change with tool aspect ratio. An additional shearing within already failed zones was also progressive in nature starting from top of the tool at an angle of 40° to 50° which was less than the theoretical angle (90°-Z) of 53°. The vertical and horizontal soil reactions were cyclic in nature and were in phase for all the tools under study. Wavelength and amplitude of horizontal soil reaction was found to increase with tool aspect ratio and depth. The stabilized surcharge took a distinct shape. The front portion was very close to quarter of an ellipsoid and the rear portion to a triangular wedge. Based on this shape, a model was developed to predict the stabilized surcharge weight. Predicted values were very close to the observed data at lower tool depths. With an increase in tool aspect ratio and depth, the observed data were found to be lower than the predicted values possibly due to the reason that the surcharge was not fully stabilized for bigger tools. The observed data and predicted values followed the same trend.