# Inversion and Analysis of the Initial Ground Stress Field of the Deep-Buried Tunnel Area
## 4 Conclusions and Discussions  
Combined with the results of hydraulic fracturing and the numerical simulation, the initial ground stress field in the tunnel area is in inversion according to the principle of multiple linear regression analysis with three coefficient estimation methods. The accuracy and rationality of the regression results are verified by comparing and analyzing with the measured data. The distribution law of ground stress and the change characteristics of lateral pressure coefficient at different buried depths and tunnel axis are obtained. The main conclusions with discussions are drawn as follows:  
1. Through the comparison and selection of three coefficient estimation methods for regression equation, to ensure the minimum mean square error and consider the multicollinearity among variables, the significance test result of the regression equation obtained by the Lasso regression method is the best, which shows a good application effect in the inversion of the initial ground stress field. In addition, with more verification of on-site monitoring results, the predictive feasibility of regression analysis can be more assured.
2. The lateral pressure coefficient along the tunnel line decreases gradually with the tunnel depth increasing. While the buried depth of the tunnel increases by 300 m, the lateral pressure coefficients of horizontal large and small principal stresses decrease by 0.1-0.3. The overall lateral pressure coefficient is in the range of 1.0-2.0, showing a relatively significant horizontal tectonism.
3. At the area near the fault, the horizontal tectonic stress is slightly released, resulting in the ratio of horizontal principal stress to vertical principal stress gradually increasing with the increase of tunnel depth. This trend is different from the analysis results of lateral pressure coefficient law beyond the fault, indicating that the influence of fault fracture zone on ground stress has gradually become one of the more dominant factors. Therefore, the lateral pressure coefficient in the super deep area needs to be determined by an on-site test. The structure of the rock massif, the position of the layer surfaces, the direction of the natural movements, the width of the fragmentation zone, etc., also have a great influence on regional in-situ stress, and the discussion and analysis of these aspects are of great research significance.  
Conceptualization, Z.T. and J.Z.; methodology, Z.T., J.Z. and R.Y.; software, X.W. and J.G.; validation, X.W., J.G. and R.Y.; formal analysis, R.Y. and J.G.; investigation, R.Y.; data curation, J.G. and R.Y.; writing--original draft preparation, R.Y.; writing--review and editing, R.Y. and J.G.; visualization, X.W. and J.G.; supervision, Z.T. and X.W.; project administration, Z.T. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
The participant's personal identification information used in the study did not include personal information. Ethical review and approval were not required for the study.  
Data sharing is not applicable.  
The authors declare no conflict of interest.