# Analysis of Collapse Mechanism and Treatment Evaluation of a Deeply Buried Hard Rock Tunnel
## 1 Introduction  
Geological disasters such as collapses, water inrush, and landslides are thorny problems in engineering construction [1; 2; 3]. The process of tunnel construction, due to the complex geological environment along the line and the geological uncertainty in front of the face, is often faced with engineering disasters such as collapses, water inrush, and large deformations, which seriously affect the safety of workers and the tunnel construction. Therefore, it is necessary to provide valuable engineering experience of tunnel collapse accidents based on the mechanism and treatment evaluation of incidents of tunnel collapse in specific environments. At present, scholars at home and abroad have done a lot of research on tunnel collapse and made significant breakthroughs. Based on data drawn from a large number of tunnel collapse cases, [PERSON] et al. [4] proposed four different collapse failure mechanisms, namely, blasting induction, groundwater action, geological environment, and the excavation method. [PERSON] et al. [5; 6; 7] analyzed the collapse mechanism of deep and shallow buried tunnels from different perspectives, such as the correlation flow law and failure criterion. According to the centrifuge test and discrete element method carried out by [PERSON] et al. [8], [PERSON] et al. [9], [PERSON] et al. [10] and [PERSON] et al. [11], the mechanism of shallow tunnel collapse disasters has beenthoroughly studied through theoretical analysis. [PERSON] et al. [12] studied the mechanism of tunnel collapse based on model tests and the influence of the arch effect and water inrush on a lining structure using numerical simulation methods. [PERSON] et al. [13] analyzed the collapse mechanism of a karst tunnel and calculated the safe thickness of the rock column, which is close to the numerical analysis results. Based on the Hoek Brown criterion, [PERSON] and [PERSON] et al. [14; 15] proposed a comprehensive analytical solution for the tunnel collapse mechanism considering an arbitrary excavation profile; a case study was selected to reveal the progressive failure evolution law of tunnel collapse using the proposed solution and other numerical methods. [PERSON] and [PERSON] [16] have studied the failure mechanism of the working face of in layered soil due to local collapse through numerical simulations. Based on a statistical analysis of a large number of tunnel collapse cases, [PERSON] et al. [17] proposed that tunnel depth, groundwater, surrounding rock level, and construction measures were the main factors affecting tunnel collapse; the influence of rainfall conditions on tunnel collapse was also studied through model tests, which indicated that groundwater has a significant impact on tunnel collapse. According to [PERSON] et al. [18], the main factors in a tunnel collapse are groundwater infiltration and the construction method, and four quick remedial measures of backfilling, reinforcement, grouting and drainage have been put forward. [PERSON] et al. [19] discussed the influence of the interface, hydrogeology and advanced geological prediction on the collapse of the tunnel and established a tunnel information monitoring management system. According to the causes of tunnel collapse, the combined treatment measures of pipe shed and grouting reinforcement, grouting and lining reinforcement, etc. were put forward [20; 21; 22; 23]. [PERSON] et al. [24; 25] and [PERSON] [26] evaluated and analyzed the treatment effect of tunnel collapse section by combined numerical simulation with on-site monitoring. Close range photography and remote sensing technology provide the possibility of structural surface measurement in tunnel monitoring [27; 28; 29; 30]. [PERSON] et al. [31] analyzed the factors influencing collapse and the instability mode of surrounding rock for tunnels crossing the fault zone with water rich soft rock and proposed joint treatment measures for inside and outside the tunnel. [PERSON] et al.