Mechanical Properties, Creep Characteristics, and Cracking Behavior of Rock-Like Materials with Parallel Double Joints of Different Thicknesses and Spacing

The impact of different types of joints in the surrounding rock on the stability of deep tunnels under external forces was investigated. Based on the uniaxial compression test, uniaxial graded loading creep test and post-creep recompression test, the mechanical properties of the rock mass with parallel double joints were analyzed, and the fracture extension evolution characteristics and energy evolution laws were examined using the numerical simulation software PFC. The results indicate that the compressive strength of the specimen increases with the increase of joint spacing. As the joint thickness increases, the compressive strength of the specimen initially increases and then decreases, and the joint thickness of 1.0 mm is the inflection point of the law change. For specimens containing double primary joints, the crack initiation stress and growth stress decrease with increasing joint thickness. When the secondary joint thickness exceeds 1.0 mm in specimens with primary–secondary joints, a sharp decrease in crack initiation and growth stress is observed. Ultimately, tensile failure, accompanied by some shear failure, is the dominant failure mode in all specimen groups. This study can provide a reference for the safe construction and disaster prevention of underground rock projects.