Experimental Study on the Bearing Mechanisms of Rock-socketed Piles in Soft Rock Based on Micro X-ray CT Analysis

Abstract

Nondestructive imaging techniques enable the study of failure mechanisms within physical models for a wide range of geotechnical problems. This paper presented an innovative experiment that utilized micro X-ray computed tomography (CT) and an in-house experimental apparatus to study the bearing mechanisms of model piles embedded in synthetic soft sandstone rock with regular triangular asperities subjected to compressive loading. X-ray CT image analyses of the model pile-load tests revealed four stages of sliding and shearing between the rock asperities and piles and the interaction mechanisms in each stage were interpreted via schematic representations. Moreover, the compression zone distribution below the model pile tip was consistent with a spherical failure pattern, which is based on the spherical cavity expansion theory. Intuitively, this study supports the applicability of the spherical cavity expansion theory for calculating the end-bearing capacity of piles socketed in soft rock. Additionally, during sliding and initial local shearing, the deformation of the surrounding rock was dominated by the cylindrical cavity expansion, which generated radial cracks inside the rock. The cylindrical cavity expansion theory and Hoek–Brown failure criterion were used to discuss the stress paths of rock of the bore wall and crack formation in the surrounding rock. To date, the effects of these radial cracks on normal stiffness of the bore wall and the bearing behaviour of rock-socketed piles have received little attention. The qualitative analyses and discussion presented in this paper provide insights into the mechanisms governing pile–rock interfacial behaviour at larger scales.