Change in the permeability of clastic rock during multi-loading triaxial compressive creep tests

Abstract

Permeability is a crucial factor for seepage analysis of porous clastic material. This research presents the change in permeability of clastic rock during multi-loading triaxial compressive creep tests. Clastic rock was cored from a critical fault zone of a hydropower station in southwestern China. Based on the physical properties and mineralogical characterisation of the rock material, a series of hydro-mechanical coupling creep tests was designed with three different confining pressures to correlate permeability and material deformation during triaxial compressive creep and reveal the effect of confining pressure on the permeability of the clastic rock. Scanning electron microscopy (SEM) was applied to identify the pore and crack features of the rock material after creep failure and consequently explain the differences in permeability at different confining pressures. The results show that the initial permeability decreased with an increase in confining pressure. During the creep tests, the permeability rapidly decreased during the initial creep and continuously decreased as material deformation increased. Near the accelerating creep, clastic rock permeability began to increase in the low confining pressure creep test but tended to stabilise in the high confining pressure creep test. This finding agrees well with the SEM results of the void features, that is, more connected pores in the sample failed under low confining pressure than under high confining pressure.