In load-structure model for tunnel design

the rock mass resistant coefficient (k) is an important parameter which affects the behavior of the tunnel structure prominently. The anisotropy of k appears due to the presence of joints. However

no adequate efforts have been made to research the anisotropic distribution of k in jointed rock masses. Ten influencing factors including the elastic modulus of rock

Poisson’s ratio

and the properties of two sets of joints were analyzed for evaluating the anisotropic distribution of k

by using orthogonal array testing strategy (OATS) and distinct element method (DEM)

with Xinggongjie Station Tunnel Project on No. 2 Line of Dalian Metro as an example. The results show that the distribution curves of k were oval-shaped. The maximum value was along the direction of the two joints angle bisector. Using the variance analysis of OATS

the significant influencing factors at the level of five percent were the elastic modulus of the rock

the normal stiffness of the joints

the spacing of the joints

and the intersection angle of two sets of joints. With the increase of the ratio of tunnel diameter to joint spacing

the anisotropy coefficient of k increased first and then started to drop

which converged to one when the ratio was equal to zero or infinite. Based on the above analysis results

the elliptic function of k was derived and was verified. The engineering example shows that the resistant coefficient of jointed rock mass is obviously anisotropic

which has little influence on the axial force of lining and remarkable influence on bending moment.