# Stress Analysis and Spalling Failure Simulation on Surrounding Rock of Deep Arch Tunnel
###### Abstract
They also noted that the degree of spalling failure was positively correlated with the initial boundary stress. For the true triaxial test, cubic red sandstone and granite specimens containing straight-walled arch holes were commonly used to simulate the spalling failure after stress adjustment following deep tunnel excavation [48]. [PERSON] et al. [49] used red sandstone specimens to simulate the spalling process and failure characteristics of \"D-shaped\" tunnel sidewalls. They found that tunnels in a \"D\" shape effectively reduced the failure severity of surrounding rock compared to circular tunnels. [PERSON] et al. [50] carried out a true triaxial test on cubic granite specimens with penetrating D-shaped tunnel and observed four stages of the spalling failure on tunnel sidewalls, i.e., the calm phase, the fine particle ejection phase, the crack generation and expansion phase, and the rock slab progressive flexural spalling phase. The spalling failure exhibited tensile characteristics. Under higher vertical stress and constant horizontal axial stress, increasing the lateral stress can reduce the severity of spalling failure and the depth of the V-shaped notch. In most underground hydraulic and hydroelectric projects, tunnels are lined with concrete to improve the self-supporting capacity of the surrounding rock, or modified materials are added to improve the strength of the backfill [51; 52]. Some scholars  
Figure 1: Rockburst disaster occurred after deep hard rock tunnel excavation [23]: (**a**) Strong rockburst in the entrance tunnel; (**b**) “7.14” rockburst in the water diversion tunnel. have combined the analytical solution of non-circular tunnels with numerical simulation software to construct a three-dimensional analysis model for analyzing the stability of the tunnel face of shallow-buried shield tunnels and deep-buried tunnel projects [53; 54; 55; 56; 57; 58]. Their research may provide relevant construction experience and suggestions for similar projects. The above investigations have greatly enriched the understanding of the stress evolution mechanism and spalling failure of surrounding rock for deeply buried hard rock straight-walled arch tunnels, and are of great guidance in revealing the formation mechanism of tunnel failure or rock instability. However, the existing research mainly focused on the stress analysis of the surrounding rock of a single hole or on indoor simulation experiments of straight-walled arch hole specimens with a single rise-span ratio \(f/B\) (the ratio of arch height to the hole width). There are few studies on the stress analysis of the surrounding rock of hole walls considering the structural parameters of the arch structure or section shape, further revealing the spalling failure. Therefore, this paper first analyses the stresses of surrounding rock of holes with arch heights of 25 mm, \(f/B=1/2\), 16.7 mm, \(f/B=1/3\), 12.5 mm, \(f/B=1/4\), straight wall heights of 25 mm and widths of 50 mm). Then, the stress analysis results were validated in combination with indoor true-triaxial compression tests. The results help further deepen the understanding of spalling failure in deep hard rock tunnels with different arch heights.