Experimental Study on Deformation Characteristics of Insitu Soft Crushed Rock Mass under Lateral Constraints

Understanding the deformation characteristics of soft and fractured rock masses is crucial for the rational design and safe construction of underground engineering projects. Based on the diversion tunnel project of the Guzhen Hydropower Station, where undisturbed rock samples were collected to conduct passive triaxial compression tests. Deformation curves of the soft fractured rock mass in the tunnel site area under graded loading were obtained. The study analyzed the time-dependent deformation characteristics using both empirical rheological models and the viscoelastic rheological model proposed by Sun Guangzhong. The results indicate that: (1) Under passive triaxial compression, the soft fractured rock mass exhibits three-stage deformation characteristics, including initial significant compaction deformation during the loading stage, relatively elastic deformation in the middle stage, and significant plastic deformation after yielding. The stable pressure stage shows accelerated deformation under relatively small axial stresses. (2) Both rheological models can effectively describe the stable pressure deformation process of the soft fractured rock samples. The parameters of the viscoelastic rheological model vary with axial loading pressure, revealing differences in time-dependent deformation characteristics during the closure-compaction stages of internal fissures within the sample.