In this paper, an experimental study is presented that intended to investigate (1) the anisotropy properties of hydraulic conductivity of Boom Clay, (2) the effect of heating-cooling cycle on the hydraulic conductivity and intrinsic permeability of Boom Clay, and (3) the effect of loading-unloading cycle on the hydraulic conductivity and intrinsic permeability of Boom Clay. Constant-head tests were carried out in a temperature-controlled triaxial cell. First, the anisotropic characteristic of hydraulic conductivity of Boom Clay with respect to its bedding was confirmed. The horizontal hydraulic conductivity (parallel to bedding) is larger than the vertical hydraulic conductivity (perpendicular to bedding).Second, there was a positive and reversible relationship between the hydraulic conductivity and temperature and a negative and irreversible relationship between the hydraulic conductivity and hydrostatic pressure.Specifically, for both horizontal and vertical hydraulic conductivity, the value at 80 °C is approximately 2.4 times larger than that at room temperature (23 °C). However, it appears that the hydraulic conductivity is not sensitive to heating rate. Data analysis reveals that under variable temperature conditions, the changes in viscosity and density of water with temperature are the main factors affecting the change in hydraulic conductivity of Boom Clay with temperature, although other factors may have an effect to some extent.3
Understanding the time-dependent behaviour of soft rock under high in situ stress is essential to the evaluation of the long-term stability of the deep-buried tunnels in expressways or coal mines. This paper presents an experimental and numerical study of the time-dependent behaviour of argillaceous red sandstone under high in situ stress. First, several triaxial creep tests for strongly and moderately weathered specimens under the confining pressure of 20-40 MPa were conducted, and the variation of time-dependent damage with time was obtained by investigating the evolution of volumetric strain during the creep process. The test results verify that creep damage has a similar effect on both axial strain and lateral strain of argillaceous red sandstone. Second, a creep damage model that is able to describe nonlinear variation in creep strain and volume expansion for sandstone under high in situ stress was established. Last, the parameters of the proposed model were determined by a back analysis method. The results of back analysis show that the model is able to describe the nonlinear variation in creep strain and volume expansion during the creep process very well.
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