Equivalent section supporting theory and its applications

The self-bearing capacity of surrounding rocks plays a significant role in roadway support. In this study,the Equivalent Section Theory (EST) has been proposed based on the reinforced arch theory and axial variation during the self-organization equilibrium process of surrounding rocks. It is considered from EST that the artificial supports help to form an elliptical-shaped self-bearing structure which takes up the majority of the true load around the roadway in the surrounding rocks and the cross-section of this structure is defined as the equivalent section. The mechanical model of roadway has been established to study the load response of the equivalent section and the relationship between the ratio of main stress to vertical stress (λ) and the axial ratio of the equivalent section ( k). It is found that the equivalent section has the smallest stress when k approaches λ,the stress demonstrates a general even distribution and the sur- rounding rocks of the roadway is in a low stress environment under this condition. The EST has been applied to exam- ine the validity of the support system of a roadway in a coal mine in Shanxi,which shows a comparable result. The the- ory can effectively examine and analyze the supporting method and provide a semi-quantitative theoretical basis for pa- rameter selection. ① The axial ratio of the roadway should be set to the optimized ratio (i. e. k = λ) where applicable; ② Pre-stressing of the bolts and cables should be carefully evaluated and additional bolts can be installed at the cor- ners to connect the stress dispersion scopes between the roof and side walls to form a complete stress ellipse;③ The first support should be timely installed when drilling in roadways with broken surrounding rocks,followed by grouting and additional pre-stressing;④ When the ground stress is large and the geological conditions are complex,a closed complete support can help form the elliptical-shaped self-bearing structure (i. e. equivalent section).