Approximate solution and numerical simulation for plastic zone of roadway surrounding rock under unequal compression in two directions

In order to obtain the solution of plastic zone in roadway surrounding rock under unequal compression in two directions,the stress of elastic zone beyond plastic zone in roadway surrounding rock is subjectively considered to be the formally same with that of elastic surrounding rock while stress constructing method is used,which is obviously un- reasonable. The accuracy of stress constructing method is relatively high in a neighborhood of the lateral pressure coef- ficient 1,while outside the neighborhood,only the plastic zone radius on horizontal (or vertical) axis can be ensured, radii on the rest locations are not accurate,or even wildly inaccurate. Meanwhile,based on the special lateral pressure coefficients 1,the radius of surrounding rock plastic zone obtained by approximate implicit method has a big error devi- ation contrasted with the corresponding analytical solution of the mature axisymmetric plane strain theory. In order to improve the shortcomings above,the surrounding rock plastic zone of non-uniform stress field on horizontal ( or vertical) axis is derived based on stress constructing method. Then the plastic zone shape is determined by approximate im- plicit method because the evolution law for general shape of circular roadway plastic zone can be well reflected by this method. Finally,the approximate radius of plastic zone in surrounding rock under unequal compression in two direc- tions is relatively accurately presented by using the similar principles. On the basis of the application of the above the- ory to the analysis of an engineering example and the numerical simulation results,the accuracy of each algorithm is compared and analyzed. The results show that the proposed method above not only eliminates the theoretical error of the approximate implicit method for the lateral pressure coefficient 1,but also overcomes the defect of that stress con- structing method can not reflect the evolution law for the general shape of circular roadway plastic zone. The solution is fairly close to the results calculated by the numerical simulation,which can be used for the approximation on the plas- tic zone in roadway surrounding rock under unequal compression in two directions instead of numerical simulation.