Improved Protodyakonov’s Method of the Tunnel Surrounding Rock Pressure under the Seepage Condition of Weak Interlayer

Table 1

Physical parameters of surrounding rock and weak interlayer.

Type	Surrounding rock	Weak interlayer
Bulk density gamma (KN/m^3)	24.9	22
Elastic modulus (MPa)	9300	2000
Poisson’s ratio of mu	0.23	0.31
Cohesion (KPa)	2160	120
Internal friction angle (°)	36.5	26
Unconfined compressive strength RC (MPa)	32.3	5
Permeability coefficient (cm/s)	5.10e-06	4.05e-08