Approximate solution on plastic zone of roadway surrounding rock under unequal compression in two directions by considering rheology

Based on the plane strain problem of roadway surrounding rock under unequal crustal stresses in two direc- tions,the effect of surrounding rock rheology on its plastic zone is studied. The deep-buried roadway sur-rounding rock usually has the characteristics of continuous deformation due to the development of rheology,and the peak stress after stabilization is the long-term strength under a certain confining pressure. Based on this,taken the surrounding rock from the bottom station roadway of the ventilation shaft at -950 m level in Hengyuan Coal Mine in Northern Anhui, China,the peak compressive strength,long-term strength and residual strength of roadway rock are measured by triaxial compression and creep tests. Considering the rock post-peak brittle softening,the roadway surrounding rock may be di- vided into elastic zone and plastic zone. On the base of the formulas of plastic zone under axisymmetric stress field in the existing literatures and the constant assumption of the total loads,the plastic zone analytical radius on horizontal (and vertical) axis of roadway surrounding rock under non-uniform stress field is derived. Then combining with the plastic zone shape determined by the method from the existing literatures,the plastic zone of surrounding rock under unequal compression in two directions is relatively accurately determined. The study shows that the result of the pro- posed algorithm is in perfect agreement with the corresponding analytical one presented in the existing literatures if the post-peak brittle softening of rock mass is not considered. The plastic zone analytical radius of circular roadway sur- rounding rock under axisymmetric stress field is a special case of the proposed algorithm for the lateral pressure coeffi- cient 1. Finally,together with the experiment data and compared the differences of considering the rock rheology to without it,the results show that the broken rock zone by considering the rock rheology is basically consistent with the engineering practice,which is the long-term strength under a certain confining pressure takes as the peak stress of sur- rounding rock. Otherwise,there will be only elastic deformation in surrounding rock,which is much different from the actural situation. It can be seen that the rock rheology has great impact on plastic zone of roadway surrounding rock. Therefore,ignoring the influence of surrounding rock rheology is actually overrating the feature of surrounding rock in theoretical research and engineering practice,which is not good for the long-term stability and safety evaluation of roadway surrounding rock.