## 4 Conclusions  
To deal with key site safety problems during the construction of tunnels in soft rock environments, such as lining damage caused by large-scale soft rock deformation, this study proposed a steel plate composite supporting structure based on the behavior of steel plate buckling. This structure was installed circumferentially, relying on steel frames to transform a rigid support structure into a yielding alternative capable of solving the problem of large-scale deformation. The feasibility of designing such a structure was established by researching model testing and experimental field construction; the following conclusions were drawn:  
1. For tunnels in the weak surrounding rock, it is often not possible to pass conventional or strengthening support structures via the available space at any one time, resulting in the need for multiple replacements and supporting works, which in turn presents a series of construction risks. To deal with the safety problems caused by the large-scale deformation of soft rock, it is necessary to optimize the supporting structure. According to the characteristic curve law of surrounding rock, under the condition of providing a degree of supporting resistance, the pressure of the surrounding rock gradually decreases with the deformation of the surrounding rock. Therefore, a deformable support design could be investigated to reduce the pressure of the surrounding rock and reduce its pressure, and finally, solve the problem of large-scale deformation of soft rock. 2. A steel plate composite structure was designed after studying the properties of Q235B steel. According to the statistical results, it can be seen that the compression of the steel plate type restrictor reaches more than 75%, which has a high compressibility. The design of the steel plate composite structure is adaptable and can be designed according to the specific requirements of the site for the initial peak and constant resistance values. Figure 19: Diagram of support stress: (**a**) concrete stress envelope diagram (unit: MPa); (**b**) stress envelope diagram of steel frame (unit: MPa). 3. According to the 3D laser scanning monitoring results, the top and bottom steel plates of the steel plate composite structure have a thickness of 1 cm, and the height of the vertical plate is 28 cm with a thickness of 8 mm. The ring structure was installed at the initial support arch waist position to form a pressure support. The on-site monitoring results showed that (a) there was no cracking of the support structure and no concrete block falling; (b) the maximum stress of the sprayed concrete was 21.01 MPa and the maximum stress of the steel frame was 209.48 MPa, which were less than the design strength, which indicated that the support structure had a high safety coefficient; and (c) there were no safety accidents, which demonstrated that, in ensuring the safety of the construction site, the problem of initial support failure of tunnels in soft and weak surrounding rocks. Conceptualization, W.W. and W.Q. ; methodology, W.Q. ; validation, W.W. and W.Q. resources, W.Q. ; data curation, W.W.; writing--original draft preparation, W.W.; writing--review and editing, W.W. and W.Q. ; visualization, W.W.; supervision, W.Q. ; project administration, W.Q. ; funding acquisition, W.Q. All authors have read and agreed to the published version of the manuscript. This research received no external funding. W.Q. ; data curation, W.W.; writing--original draft preparation, W.W.; writing--review and editing, W.W. and W.Q. ; visualization, W.W.; supervision, W.Q  
* _[PERSON] et al. (2021)_ [PERSON]; [PERSON]; [PERSON]; [PERSON] [PERSON] Resistance-Limiting and Energy-Dissipating Support for Deep Buried Old Loess Tunnel. _China Railway Sci._**2021**, _42_, 88-97. [CrossRef]
* _[PERSON] et al. (2005)_ [PERSON]; [PERSON]; [PERSON]; [PERSON] Research on large deformation and its mechanism of Muzhailing tunnel. _[PERSON]/[PERSON] Rock Mech. Eng._**2005**, _24_, 5521-5526. (In Chinese)
* _[PERSON] et al.