Instability Process of Crack Propagation and Tunnel Failure Affected by Cross-Sectional Geometry of an Underground Tunnel

Table 1

The principle of determining physical model parameters.

Category of parameter	Physical parameters	Similarity ratio equations	Remarks
Geometric parameters	Height, H		It is determined by using the geometric parameters of the field tunnel and the physical model, KH = KR = 1/15
	Span/radius, R
	Density, ρ
Gravity parameter	Gravitational acceleration,		For the same gravitational field,
Intensity parameter	Tensile strength, Rt
	Compressive strength, Rc
	Cohesion, C
	Internal friction angle, φ
Deformation parameters	Poisson’s ratio, μ
	Elasticity modulus, E