# Analysis and Application of Lining Resistance to Water Pressure in Tunnel through Karst Cave
## 6 Conclusions  
In this paper, on the basis of the Xin Yuanliang Mountain Tunnel Project, the hydraulic pressure resistance and damage process of composite structures in tunnels with karst area were analyzed using RFPA software to reveal the disaster-causing mechanism under high water pressure. The construction plan of the parallel heading expansion of the Xin Yuanliang Mountain tunnel was discussed and verified by field testing. The main research conclusions obtained were as follows:  
(1) The rupture characteristics of grouted stone around the tunnel induced by tunnel expansion construction were explored from the perspectives of mechanics and acoustic emission. The results showed that the cracks were mainly caused by tensile-shear damage, and the whole damage process could be divided into three stages: the growth phase, stabilization phase, and violent damage phase.  
(2) By comparing the field monitoring data with the model calculation results in the paper, it was found that the earth pressure obtained from the model calculation was similar to the actual monitoring results, with an average error of about 0.01 MPa; the water pressure was smaller than the actual results by about 0.03 MPa, due to the idealization of the model grouting parameters. Overall, the model has good reliability and can be used to guide the practical engineering applications.  
(3) The New Yuanliang Mountain Tunnel was constructed through a high-pressure water-rich cave, which has a large volume, large water volume, and high water pressure, with a maximum water pressure of 3.0 MPa in the rainy season. According to the numerical model, the project finally adopted a 5 m grouting range and temporary secondary lining of the core section of the cavity. The monitoring results showed that the water pressure behind the lining was only 0.04 MPa at this time, ensuring the safety of the construction through the cavern.  
(4) To address the problem of the high risk of expansion construction in the karst cave section of the new Yuanliang Mountain Tunnel, an improved construction technique of expansion of reserved core soil based on the CRD method was proposed. This method supports the lining structure of the existing parallel heading with a temporary steel frame, which makes full use of the support capacity of the existing parallel heading lining. After the deformation of the ring initial support steel frame is stabilized, and the existing lining and internal temporary steel frame are removed, the displacement of the surrounding rock can be reduced by about 50%, ensuring the safety of the tunnel expansion.  
Conceptualization, J.L.; methodology, M.H.; writing--review and editing, J.L. and Y.S.; funding acquisition, M.H.; formal analysis, Z.Y. and Z.Z. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Natural Science Foundation of China, grant number 51878037.  
Not applicable.  
The authors would like to thank [PERSON] and [PERSON] for their help at the construction site. The authors would like to thank the anonymous reviewers, the academic editor, and the assistant editor for their valuable comments that helped improve the paper's quality.  
The authors declare no conflict of interest.