## 6 Discussion and Conclusions
### Conclusions  
This paper provides a theoretical basis for the excavation of a super-large cross-section roadway in the integration of 'excavation-filling-retention' for interface coal pillars. Based on the theory of the complex variable function, the stress distribution law of surrounding rock during the excavation of super-large cross-section roadway was analyzed, and numerical simulation software was used for a supplementary analysis and verification. The maximum range of the plastic zone and the deformation and failure characteristics of surrounding rock during the excavation of a super-large cross-section roadway were obtained, which is of great significance to the implementation of surrounding rock control for a super-large cross-section roadway. According to the above analysis, the following main conclusions can be drawn:  
1. When the side-pressure coefficient remains unchanged, with an increase in aspect ratio, there is greater stress upon the two side walls of the roadway, and less stress upon the roadway roof; moreover, with that increase in aspect ratio, the numerical transition in roadway stress upon the side walls flattens, while the such transition in its roof becomes more intense; when the roadway aspect ratio is larger than 4, more than 70% of the roof area will be subject to a weaker stress. 2. When the roadway aspect ratio remains unchanged, there are two side-pressure coefficient threshold values \(\lambda_{\rm up}\) and \(\lambda_{\rm down}\) between which all stresses upon the surrounding rock of the roadway are compressive stresses. As the aspect ratio of the roadway increased from 1 to 9, its \(\lambda_{\rm up}\) increased from 1.823 to 5.865 and its \(\lambda_{\rm down}\) increased from 0.549 to 0.888. When those side-pressure coefficients in the environment where the roadway is located exceed their critical values, tensile stress will take place on the roadway boundary and result in tensile failure, thus leading to instability in the roadway super-large sections. 3. By means of numerical simulation, the elastic solution law in theoretical calculation was verified by the Mohr-Coulomb constitutive method. Accordingly, with the increase in the aspect ratio of the roadway, these compressive stresses upon both sides of the roadway increase, and so do these tensile stresses upon both the roof and baseplate of the roadway; with the increase in the side-pressure coefficient of the roadway, these stresses upon both sides of the roadway decrease, and these compressive stresses upon both the roof and base plate increase, while the tensile stresses upon both the roof and base plate decrease; the roadway is more vulnerable to failure accordingly. It can thus be seen that laws drawn from elastic solutions apply to the elastic-plastic model as well, and therefore can create a theoretical basis for surrounding rock control in coal mining engineering and lay a theoretical foundation for the excavation of roadways with super-large sections. * The impact of the side-pressure coefficient upon the plastic zone range of roadway surrounding rock is greater than the impact of the roadway width. In order to ensure stability in the surrounding rock of a roadway with super-large sections during its excavation process, the side-pressure coefficient should remain around 1; in this situation, the plastic zone covers the smallest range and takes an approximate \"elliptical\" shape, and the relevant support work is the easiest. When the roadway width exceeds 25 m, the plastic zone on the roadway roof will see malignant expansion, and difficulty in support will increase intensely, rendering all effective support impossible; when the roadway width is less than 25 m, the roof can be controlled by a lengthened anchor cable and highly extended anchor bolt. This article is presented by the seven authors mentioned, each of whom were responsible for various aspects of the work. Conceptualization, B.Z. and H.C.; methodology, B.Z. and H.C.; software, H.C., J.W. ([PERSON]) and Y.T. ; validation, H.C., R.W. and Z.Y.