Study on Energy Release of Surrounding Rock under the Multiple Unloading Disturbance during Tunnel Excavation

Table 2

Hoek–Brown mechanical parameters and in situ stress field.

Compressive strength	Elasticity modulus	GSI		mb
140 MPa	45 GPa	70	9	3.0827
		Strength of extension	Poisson ratio	Bulk modulus
0.0357	0.5	1.6 MPa	0.24	28.8 GPa
Shear elasticity	The horizontal direction: σxx	The axial direction: σyy	The vertical direction: σzz
18.1 GPa	39.7 MPa	34.9 MPa	58.3 MPa