## 4 Stress Distribution Characteristics of Roadway Surrounding Rock
### Influence of Aspect Ratios on Stress Distribution for Surrounding Rock in Rectangular Roadways
Influence of Side-Pressure Coefficient on Stress Distribution for Surrounding Rock in Rectangular Roadways  
In order to study the laws on the influence of different side-pressure coefficients on the stress distribution in the surrounding rock of rectangular roadways, tangential stresses upon the roadway in those nine models were calculated when the vertical force was \(P_{0}\) and the acting points \(b/h\) were from 1 to 9. In Figure 7, tangential stress distribution curves are given of roadway surrounding rock under different side-pressure coefficients. Here, the curves of the stress distribution in the surrounding rock of rectangular roadways are displayed under five conditions, where the side-pressure coefficients \(\lambda\) were 0, 0.5, 1, 1.5 and 2, respectively. As shown in Figure 7, depicting the tangential stress distribution curves of roadway surrounding rock under different side-pressure coefficients, the stress on surrounding rock on the boundary varied relatively flatly along the two side walls and on the roof and the base plate, and the stress changed abruptly when it reached the roadway corner. When \(\lambda\) was equal to 0, the tensile stress in the roof center and the base plate center of the roadway changed mildly from 0.81 to 1.06 \(P_{0}\) with the aspect ratio; when \(\lambda\) was larger than 0.5 but smaller than 1, tensile stress appeared in the roof center of rectangular roadways. The \(\lambda\) value corresponding to tensile stress in the roof varied depending upon the roadway's aspect ratio; when \(\lambda\) was smaller than 0.5, tensile stresses appeared in the roofs of rectangular roadways with different aspect ratios. From the perspective of roadway safety, a reinforced roof anchoring is necessary in this case so as to prevent the roof's pulling failure and further bed separation breaking. When \(\lambda\) was equal to 1, the tangential stress on both side walls of the roadway increased by 6.3 times from 0.67 \(P_{0}\) to 4.23 \(P_{0}\) with the increase in the roadway's aspect ratio from 1 to 9; tangential stresses on both the roof and base plate of the roadway decreased by 0.2 times from 0.67 \(P_{0}\) to 0.14 \(P_{0}\); when \(\lambda\) was equal to 1.5, compressive stress was present around the rectangular roadways; in this case, the surrounding rock's modification and reinforcement can be achieved by grouting support, and we sprayed concrete on the two side walls so as to avoid the adduction of the two side walls due to shear failure from surrounding rock stress, and thus to safeguard the normal operation of the roadway [42]. When \(\lambda\) was equal to 2 and \(b/h\) was equal to 1, the two side walls were damaged by tensile stress; when \(b/h\) was larger than 1, compressive stress was present around the rectangular roadways; when \(\lambda\) was larger than 2, the tension damage could be resolved by increasing the aspect ratio of the roadway [32]. When the side-pressure coefficient \(\lambda\) was constant, the stresses upon both side walls increased with the increase in the aspect ratio, while the stresses upon the roof and base plate decreased with the increase in the aspect ratio; however, such changes in stress were mild. In theory, the stress at the angular point should be infinite, while, in practice, circular arc transition must be adopted for the angular point; otherwise, a computation result will be impossible. According to the stress distribution at the corner, there is no obvious regular correlation between the maximum stress and aspect ratios. When an arbitrary value was assigned to the side-pressure coefficient \(\lambda\), compressive stress concentration took place at all of the roadway corners. Therefore, corner support still deserves due attention.