Experimental methods and creep testing study of undisturbed cataclastic weak rock under lateral confinement

Cataclastic weak rock masses, commonly found in tunnel and slope engineering projects in Southwest China’s mountainous regions, are formed in tectonically active zones and exhibit significant structural disturbance. This disturbance greatly impacts their mechanical behavior in engineering contexts. However, obtaining undisturbed samples for laboratory testing is challenging, and research on their mechanical properties is limited. For cataclastic weak rock masses, some major engineering projects primarily rely on in-situ testing to obtain their mechanical properties. However, such field tests are costly, time-consuming, environmentally constrained, and offer limited controllability. This study proposes a specialized sampling and testing method for cataclastic weak rock masses. The method systematically describes the sampling procedure and testing principles. Considering the interaction between the sample, sampling cylinder, and force-transmitting plate, a mechanical model for the “sample–sampling cylinder–force-transmitting plate” system is developed. The results show that the double series method, combining the Fourier and Fourier-Bessel series, effectively solves the spatial axisymmetric mechanical problem of the model. The axial pressure, confining pressure, and lateral shear stress on the specimen exhibit symmetric exponential distributions. Creep parameters under lateral confinement were identified through displacement back-analysis in FLAC3D using a pattern search algorithm. The testing method proposed in this study enables the investigation of deformation characteristics of cataclastic weak rock masses while preserving their original structure, providing a novel approach for obtaining mechanical parameters of rock masses in related engineering projects.