Abstract: This study aims to examine the mechanical responses and deformation damage mechanisms of deep jointed rock masses during transient unloading. We investigated the mechanical behavior and dynamic responses of these rock masses during transient unloading through theoretical analyses, laboratory experiments, numerical simulations, and other methods. Our research identifies several key factors influencing the dynamic response to transient unloading in jointed rock formations. We develop a numerical model that describes in-situ field conditions closely. Initial findings reveal that in the first stage of uniaxial transient unloading, the rock mass experiences no tensile stress. However, in the subsequent second stage, the reflection of tensile stress waves transforms all kinetic energy into elastic potential, creating tensile stresses within the rock mass. Additionally, the unloading process generates transreflectance at rock joints, leading to an inverse relationship between joint opening and stiffness in the presence of joints. In the second stage of uniaxial transient unloading, significant joint opening occurs, causing a sudden displacement in the rock mass as the reflected tensile stress wave reaches the joint. This research enhances our understanding of the mechanical behavior of rock masses under uniaxial transient unloading, providing valuable insights for addressing transient unloading challenges in deep rock mass excavations.

Key words: deep rock mass, jointed rock mass, transient unloading, damage mechanics, numerical analysis