Based on basic theory of unloading rock mass mechanics

a simulation method of unloading which the change intervals of plastic volumetric strain increment are corresponding to mechanical parameters of rock masses in different unloading zones is put forward by using three-dimensional finite difference software. Changes of the maximum volumetric strain increment and damage area of surrounding rock at different lateral pressure coefficients combination conditions are simulated. The results of numerical simulation show that

the external surface of area of plastic volumetric strain increment near the hole wall is approximately like an vertical oval at lower lateral pressure coefficient. With the lateral pressure coefficient increasing

the external surface of area of plastic volumetric strain increment becomes more rounded

and finally to a horizontal oval. The greater the lateral pressure coefficient

the unloading effect of surrounding rock is more significant and plastic volumetric strain increment of surrounding rock near the hole wall is greater

so the damage area of surrounding rock is correspondingly greater. The results provide foundation for the stability analysis of deep tunnel and supporting design of the cracked surrounding rock.