The major reason of the failure of jointed rock-mass is the formation of the plastic zone near the crack tip ofⅠ-Ⅱmixed crack which leads to the growth,propagation of the branched crack under load condition.In the paper,the failure judgment of mini-plastic zone's displacement is derived by the Mises yielding rule.The anchor cable is simulated by the different link elements and inflicting pre-strains according to the difference of mechanism of the consolidated segment and free segment.The stress and strain fields near crack tip of twain collinear cracks of different angles and consolidated conditions are simulated by iso-parametric element with eight nodes.The iso-parametric element with eight nodes is degenerated to singular element at crick tip to simulate crack.It is shown that the mini plastic zone's displacement near the crack tip begins to increase,then decreases with the increase of the angle of the crack.The better consolidated condition is,the smaller the angle of crack tip is when the mini plastic zone's displacement near the crack tip arrives at the biggest value.The mini plastic zone's displacement near the crack Tip 2 is bigger than that near the crack Tip 3.The crack is easier to failure with the increase of load.
