## 5 Conclusions  
In view of the surrounding rock deformation and failure problems, such as spray layer cracking, sheet slope buckling, and steel arch buckling, in a deep buried high stress and small-clearance tunnel in southwest China, the asymmetric failure characteristics of the surrounding rock are clarified through failure investigation, geological analysis, and surrounding rock pressure monitoring. The evolution characteristics of the surrounding rock pressure of different tunnels are analyzed, and combined with geology, excavation and surrounding rock pressure, the asymmetric failure mechanism of the surrounding rock during the excavation of deep buried small-clearance tunnel is revealed. The following four conclusions are presented:  
(1) A monitoring method for the surrounding rock pressure in a deep buried small-clearance tunnel is proposed. A group of single-row pressure sensors is arranged in the advance tunnel to determine the mileage of the monitoring section. When the two left and right lines are followed up by the backward tunnels, the second group and the third group of pressure sensors are installed in turn at the monitoring section. Considering the stress of the deep valley, the excavation effect, and the adverse structural influence of the rock mass, the surrounding rock pressure monitoring method with eight sensors in each monitoring section and local dense arrangement is determined.  
(2) In the process of excavation of the deep buried small-clearance tunnel, the surrounding rock failure is asymmetrical, which shows that the surrounding rock pressure of the tunnel is more serious on the valley side than the mountain side. In the backward tunnel, the damage degree of the left line is the least, followed by the right line. In the advance tunnel, the parallel pilot tunnel pressure is the most serious, especially in the sections after the excavation of the left and right lines.  
(3) The surrounding rock pressure in the excavation process of the deep-buried small-clearance tunnel can be divided into five periods. The spatial evolution trend of the surrounding rock pressure on the monitoring section is that the growth rate in the arch is greater than that in the side wall, and the growth rate in the valley is greater than that in the mountain side. The pressure distribution characteristics of the surrounding rock are asymmetrical.  
(4) High ground stress is the main cause of failure of the surrounding rock during excavation of the deep buried small-clearance tunnel. Under the influence of the deep valley stress, the stress concentration of the surrounding rock on the valley side is greater than that on the mountain side. In the follow-up process of the backward tunnel, tangential stress concentration occurs on the valley side of the advance tunnel under the influence of the deep valley stress and excavation disturbance. Since the energy and stress around the surrounding rock are fully released and transferred under the excavation of the first tunnel, the backward tunnel is relatively stable.  
Conceptualization, Q.S. and G.-L.F.; funding acquisition, G.-L.F.; validation, W.N.; investigation, W.Z. and W.N.; resources, G.-L.F.; data curation, W.Z.; visualization, X.W. and J.C.; writing--original draft, W.Z.; writing--review and editing, Q.S., G.-L.F., and W.N. All authors have read and agreed to the published version of the manuscript.  
The research was funded by the National Natural Science Foundation of China (No. 42177168) and the Hubei Natural Science Foundation (No. 2024 AFA068).  
Not applicable.  
Data Availability Statement: The raw data supporting the conclusions of this article will be made available by the authors on request.  
The authors declare no conflicts of interest.