Evaluation on strength and deformation behavior of red sandstone under simple and complex loading paths

Triaxial compression experiments were carried out for red sandstone to investigate its strength and deformation failure behavior under simple and complex loading paths. In this research, tested confining pressure is in the range from 5 to 35 MPa. Under simple loading path, the peak strength, residual strength and critical damage threshold of red sandstone all increase with the confining pressure, which are in good agreement with the linear Mohr-Coulomb criterion. To investigate the re-fractured mechanical behavior of pre-cracked red sandstone with different post-peak stress drops, two complex loading paths with only one specimen are put forward to obtain the strength and deformation parameters of red sandstone. The differences of strength and deformation parameters of red sandstone between simple and complex loading paths are evaluated detailed. The elastic moduli of red sandstone under simple and complex loading paths all increase nonlinearly with the confining pressure. It is suggested and recommended to predict the peak strength of rock under simple loading path by adopting complex loading path A (increasing gradually the confining pressure) not complex loading path B (reducing gradually the confining pressure). On the basis of the linear Mohr-Coulomb criterion, a kind of new method is put forward to revise the peak strength of red sandstone under complex loading path A, which is testified to be right and reasonable. The investigated conclusions are very significant for ensuring the stability and safety of deep underground rock engineering.