Experimental study on mechanical properties of deep sandstone and its constitutive model

In order to investigate into the negative impact of the deterioration characteristics of rock strength on the sta- bility of deep mining engineering structure, the triaxial compression tests on the sandstone samples collected from Hongqingliang Deep Shaft Project are performed under different confining pressures. With reference to Mohr-Coulomb strength theory,the stress-strain,strength,and deformation characteristics of the sandstone are analyzed. The damage and softening constitutive model of the sandstone is deduced,given that the damage variables are subject to Weibull distribution. The functional relationships between the model parameters ( F0 and m) and the confining pressure are discussed. Based on the influence of model parameters on the constitutive model and the changing characteristics of the stress-strain curve,the nonlinear fitting method is employed to modify the model,hence the modified damage and sof- tening constitutive model is obtained. The modified constitutive model is numerically solved by FLAC3D ,and the theo- retical computation results are compared and verified against the complete stress-strain curve of the sandstone. The modified constitutive model is applied in engineering projects through the construction of the numerical model for sur- rounding rocks of the in-gate cavern,and the rationality of the numerical computation results is analyzed. The results show that:① the deformation parameters have low sensitivity to confining pressure,while the strength parameters are significantly affected by confining pressure. Under different confining pressures,when the stress is at its peak,the sand- stone displays obvious strain softening characteristics. ② Based on the numerical verification results of the FLAC3D ,the stress-strain curve obtained from theoretical computation using the damage and softening constitutive model is highly consistent with the experimental curve,indicating that the model is highly reliable and can reflect the complete damage process of the sandstone under complex stress conditions. ③ When numerical simulation approach is employed to ana- lyze the failure law of surrounding rocks and supporting structures of the deep in-gate cavern,a plastic shear strain fail- ure is more likely to occur on the vault and the spandrel,which are essentially the same as the failure position and range of supporting structures in real engineering projects.