Table 1: Evaluation factors and grading standard.

FactorsStability grade
Stability
(I)
Relative stability
(II)
General stability
(III)
Instability
(IV)
Very instability
(V)

(1) Rock quality designation (RQD)/%>9075–9050–7525–50<25
(2) Rock uniaxial compressive strength/MPa>12060–12030–6015–30<15
(3) Rock mass integrity coefficient>0.750.45–0.750.3–0.450.2-0.3<0.2
(4) Strength coefficient of structural face>0.80.6–0.80.4–0.60.2–0.4<0.2
(5) Groundwater seepage (L/min·10 m)<55–1010–2525–125>125