Measurement of stresses and strains around a pushed-in model pile or cone penetrometer

Abstract

This paper describes the methods and outcomes of tests designed to simulate the penetration of a pushed-in model pile, or a field testing penetration element. The penetration element was a 25 mm dia. cylinder with a conical tip. The element was advanced into a sand profile subjected to vertical pressure under at-rest conditions. The unique aspect of the testing was the inclusion of in-soil measurement tools. Null soil pressure gauges were used to monitor radial pressures and in-soil linear strain devices were used to monitor radial strain at points within a measurement horizon as the penetration element was advanced into the profile. Testing revealed that radial pressures return to their ambient pre-penetration magnitudes once the element passes below a sensing horizon. In-soil radial strain measurements illustrated that the rapid drop in radial soil pressure coincides with a small, but consistent reversal in the increment of radial strain. As distance from the axis of penetration decreases this reversal is more significant. These observations have importance in considering the development of frictional resistance and axial capacity of pushed-in piles and at the same time have relevance to the analysis of cone penetration testing in the determination of rational material properties.