Experimental study on permeability evolution during deformation and failure of shaft lining concrete

This paper presents an experimental study on shaft lining concrete specimens under different confining and pore pressure difference. The initial permeability, peak strength, relationship between the axial strain, volumetric strain and permeability; and the failure morphologies of the shaft lining concrete were investigated. The experimental results indicate that, for a constant confining pressure, the shaft lining concrete initial permeability increased and the peak intensity decreased with increasing pore pressure difference. This phenomenon is mainly related to the initiation and propagation mechanism of micro-fissures in the concrete. The entire process of specimen deformation is divided into four stages: nonlinear compaction, linear elastic, elastic-plastic and peak strengthening, and strain softening. Permeability-axial strain and stress-axial strain curves generally showed three trends. During the strain softening stage, the permeability curve showed increasing, flat and decreasing trends with changes in the confining pressures. The flat permeability is a new phenomenon in triaxial experimental research. Volumetric strain exerted a certain influence on permeability in that permeability decreased with increasing volumetric strain during the brittle-ductile transition stage. The failure modes of the specimens were mainly oblique shear failures. With increasing pore pressure difference, surface cracks in the specimens increased and more serious failures were encountered. (C) 2018 Elsevier Ltd. All rights reserved.