Hydromechanical behaviour of columnar jointed rock masses under true triaxial conditions: An experimental and theoretical investigation

Understanding the hydromechanical behaviour of columnar jointed rock masses (CJRMs) is crucial for reservoir evaluation in oil and gas engineering and dam foundation stability control in water conservancy projects. According to the natural structural characteristics of the CJRM, artificial samples with diverse dip angles (& beta; = 0 degrees -90 degrees) were poured through the self-designed mould, and several true triaxial seepage tests had been done. Based on the test results, the anisotropy of the permeability and the stress sensitivity of the CJRM at different loading stages were discussed, and a two-stage permeability model was established according to the change in volumetric strain. Under the true triaxial conditions, the seepage characteristics of the CJRM have strong stress sensitivity, showing obvious U-shaped seepage variation characteristics. The existence of the dip angle greatly affects the anisotropic seepage characteristics as well as the failure mode of the CJRM, when the dip angle is between 45 degrees and 75 degrees, the failure mode is mainly structural failure, and the volume expansion is the most intense. Finally, the two-stage permeability model that proposed in this study is fitted with three groups of different experimental data, and the fitting results show the model can effectively reflect the variation law of the permeability characteristics under full stress conditions, indicating that the volume strain as a characterization parameter for predicting the change in permeability characteristics has strong applicability. The research results can make a more effective understanding of the permeability variation characteristics of jointed rock masses.