Effect of intermediate stress on permeability of sedimentary rock under true triaxial compression

Abstract

In this paper, we conducted lab-scale experiments on siliceous mudstone from Horonobe URL to study the effect of the stress state of rock mass during the excavation of underground openings on their mechanical and hydraulic properties. A true triaxial testing apparatus was used to simulate the changes in the stress field of sedimental rock mass around the opening. A hydraulic line was equipped in two principal directions allowed direct measurement of permeability anisotropy during the test. Two stress states, before and after excavation, were considered to simulate the stress field near the opening. Besides, two intermediate principal stresses were also considered so that rock failure occurred in the stress field corresponding to the top and sidewalls of the opening. The results of siliceous mudstones show that the permeability can be lower under residual stress after macrocrack failure than under intact initial stress. Studies on the effect of crack direction and stress field changes on permeability are limited, especially in sedimentary rocks, and therefore, the results of this study can contribute to the development of a coupled hydraulic-mechanical model with a proper constitutive model to evaluate the excavation damage zone.