Approximate solution of plastic zone in deep soft roadway surrounding rock under unequal stress field in two directions considering rheology

The surrounding rock of deep soft rock roadway usually shows an obvious rheological property.In order to determine the elastoplastic interface of surrounding rock in deep soft roadway under unequal stress in two directions, the stable roadway surrounding rock is directly taken as the research object by skipping the complex rheologic deformation process of surrounding rock.Based on the fact that the peak stress of stable surrounding rock in deep-buried soft rock roadway is the long-term strength under a certain confining pressure, surrounding rock is divided into elastic zone, plastic softening zone and ruptured zone by considering post-peak strain-softening of rock mass.On the basis of the formulas of plastic zone under axisymmetric stress field and the constant assumption of total loads, the plastic zone analytical radius on horizontal (and vertical) axis of deep soft rock roadway surrounding rock under non-uniform stress field is derived.Then combining with the plastic zone shape determined by the method of the existing literature, the plastic zone of surrounding rock under unequal compression in two directions is relatively accurately determined.Finally, based on the application of above theory to the analysis of an engineering example, the differences between considering rock mass's rheology and without considering it are compared.The results show that plastic zone distributition is relatively reasonable if rock mass's rheology is in consideration, otherwise the plastic zone will distribute in a very small range of surrounding rock in a form of sliding wedge, which means surrounding rock almost only produces elastic deformation under this circumstance.It can be seen that rheology has great impact on the plastic zone of roadway surrounding rock, and the plastic zone is relatively small if the rheologic property of rock mass is not considered.It is better to take rock mass's rheology into account in theoretical research and engineering practice, so that the long-term stability and safety of roadway surrounding rock can be ensured.It is found that the result of the proposed algorithm in this paper is in perfect agreement with the corresponding analytical one presented in the existing literature if the post-peak strain-softening of rock mass is not considered, and is close to that of the finite element method.Therefore, the algorithm can be used as a relatively reasonable and accurate estimation method for quantifying the plastic zone of deep soft roadway surrounding rock under unequal stress in two directions.