## 6 Conclusions  
This paper revealed stress field distribution and deformation law in a large deformation tunnel of soft rock. Theoretical analysis, numerical simulation and field monitoring were employed to investigate the surrounding rock stress and displacement state, evaluate the plastic zone radius, optimize the initial support and propose a reasonable reserved deformation. The following conclusions are drawn:  
1. The bolt length can be determined by the radius of the plastic zone. During the construction of a small section tunnel, bolts need to be lengthened several times to form long bolts, and long boreholes are easy to collapse, which is very disadvantageous to the construction period. Short bolts (4.5 m) are used to fix the steel arch on the surrounding rock horizontally and increasing the number of bolts effectively controls the occurrence of large deformation in soft rock mass.
2. The short bench method can effectively control the deformation of surrounding rock and the plastic zone. In order to reserve enough working intervals on the bench in actual construction, the optimal bench length is about 1.5-2 D of the tunnel.
3. With the reinforcement of tunnel support and the advance of supporting construction time, the peripheral displacement and radius of plastic zone of tunnel decrease, so the support stiffness and supporting time can be optimized. On the premise of making as much use of the bearing capacity of the rock mass as possible, the second lining should be constructed early. The displacement can be effectively controlled by constructing the second lining in time at the position about 2 D from the tunnel face.
4. The reasonable reserved deformation should be considered in the excavation of a soft rock tunnel to avoid secondary expanding excavation. The reserved deformation in different parts and different sections of the tunnel may be different and it is necessary to make the pertinent adjustments. Through numerical simulation and field monitoring, the reserved deformation was  
Figure 11: (**a**) Typical cross-section 1 of middle part of tunnel; (**b**) Typical cross-section 2 of middle part of tunnel.  
Figure 12: (**a**) Typical cross-section 1 of terminal part of tunnel; (**b**) Typical cross-section 2 of terminal part of tunnel.  
finally determined to be 10-35 cm. In addition, in consideration of the measurement uncertainties, a Bayesian approach can be applied to predict deformations to adjust the value [48].
* The construction, monitoring and measurement of tunnel in soft rock must be strengthened. By collecting rock mass deformation information, the stability state of the rock-supporting system, the rationality of supporting structure parameters and construction methods can be determined. Based on the feedback information, the size of the reserved deformation, support design and operation time can then be optimized, respectively.  
[PERSON] analyzed the calculation results and wrote the article; [PERSON] carried out the numerical simulation; [PERSON] processed the data; [PERSON] provided the construction site information; and [PERSON] offered useful suggestions for the preparation and writing of the paper.  
The study was supported by the National Natural Science Foundation of China (NSFC) under Grant No. 51508037.  
We also highly appreciate the contribution of data collection from Datang Sichuan Power Generation Co., Ltd. Finally, the authors would like to thank reviewers for useful comments and editors for improving the manuscript.  
The authors declare no conflict of interest.