Study on the Application of the Kent Index Method on the Risk Assessment of Disastrous Accidents in Subway Engineering

Table 6

Risk occurrence mode of face instability and the related indexes.

Occurrence mode	Comprehensive mode
Related indexes
Basic indexes (no.)	Affects the limit support stress ratio (B1); Change of strata (B2); Overbreak of the affected strata (B3)
Design indexes (no.)	Shield-excavating equipment design (D1); Shield-pushing equipment design (D2); Strata adaptability of the shield (D3)
Construction indexes (no.)	Level of the construction technology (C1); Construction period (C2); Construction environment (C3); Control measures (C4)

The limit support stress ratio is the ratio of the value of limit support stress to original lateral geostress, where the limit support stress refers to the minimum stress that can support face stability.