Minor joints exist ubiquitously in deep-buried brittle rock masses subjected to high in-situ stress. These joints affect the strength and deformation properties and lead to the concentration and dissipation of stress wave propagation. Through modeling and verification, the rock mass model in the study with closable minor joints can perform the plasto-elastic behavior under static compression, and the increase of wave velocity with confining stress under dynamic load. The unloading response of tunnels is analyzed in two influencing factors: unloading rate and lateral stress coefficient. According to the results, the increase of unloading rate will intensify stress oscillation and increase additional dynamic stress disturbance of the joint rock mass near the tunnel boundary. As the vibration dissipates kinetic energy, the additional dynamic stress disturbance farther away from the tunnel boundary is decreased. Additionally, the minor joints can open or close in particular directions depending on the complex in-situ stress and the stress distribution of the surrounding rock mass. At the location along the direction of open joints and close to the stress release source, the joint rock mass may have a higher additional stress concentration than in the elastic model.
The scarcity of shallow mineral resources and construction space has substantially escalated the depth of tunnel excavation (Li et al., 2017; Xie et al., 2015). Deep rock mass subjected to gravitational and tectonic stress reserves enormous strain energy and exhibits evident fracture development. Deep tunnel excavation is typically a dynamic unloading process (Cai, 2008; Lu et al., 2012). In particular, the strain energy will be immediately released within several milliseconds and induce a pulse load when the tunnel is excavated utilizing drilling and blasting (Yang et al., 2013). This process may lead to various observed hazard phenomena, such as spalling (Jiang et al., 2013), rock burst (Ortlepp & Stacey, 1994), large deformation (He et al., 2005), and zonal disintegration (Jia & Zhu, 2015). Meanwhile, the intensity and frequency of disasters escalate as excavation depth increases, threatening construction and operation safety (Cai, 2016). Therefore, the mechanism of unloading failure of deep tunnels in rock mass has always attracted the attention of many researchers.
