Laboratory Experiment of Soil Vertical Displacement Measurement Near an Axially Loaded Pile

Abstract

The paper presents the results of static pile load test in laboratory conditions with additional measurement of vertical displacement of soil surrounding the shallow embedded pile. The main purpose of research to determine the pattern of soil displacement due to axial load of the pile. Although, the dimensions of pile are strongly differing from field pile used in practice, there are some phenomena which are similar to natural conditions. Tests were performed on a small precast concrete pile which was 7 cm in diameter and 25 cm long embedded in cohesionless soil. The measurements of the study were: applied load, resistance under the toe of the pile, settlement of the pile and vertical displacement of chosen points in the soil near to the toe of the pile. Performed test indicated that in small load the displacement in soil increase due to increasing load, but when the load was approaching the value of ultimate load, displacement stopped and at the limit load the direction of displacement vector changed to upward. The shape of the shear failure mechanism took the form of a logarithmic spiral which was widely described in literature. In this study an attempt at mathematical description has been made. In the proposed approach it was assumed that the displacement of the pile influenced the change of the sphere volume under the pile base which affects the displacement of the selected points of the soil. The research allowed to determine the size of ground space which was affected by the studied pile. The other studies indicate that the failure mechanism in deep piles and poorly compacted soils is caused by punching shear failure when only soil displacement down occurs, but in very compacted sands the mechanism of failure would be similar to obtained in laboratory test.