| | The level of surrounding rock | Main qualitative characteristics of surrounding rock or soil | Basic quality index of surrounding rock (BQ) or modified basic quality index of surrounding rock [BQ] |
| | I | Hard rock, rock integrity, giant monolithic or thick bedded structure | >550 |
| | II | Hard rock, rock integrity, massive or thick bedded structure | 550–451 | | More hard rock, complete rock mass, massive overall structure |
| | III | Hard rock, rock mass is broken, huge block (stone) broken (stone) mosaic structure, harder rock or more soft and hard rock, rock mass is more complete, massive or thick layer structure | 450–351 |
| | IV | Hard rock, fractured rock mass, cataclysmic structure | 350–251 | | More hard rock, rock mass more broken ∼ broken, mosaic fracture structure | | Soft rock or interbedded soft and hard rock, and mainly soft rock, the rock mass is more complete ∼ more broken, medium thin bedded structure | | Soil: ① compacted or diagenetic cohesive soil and sandy soil; ② loess (Q1, Q2); ③ general calcium, iron cemented gravel soil, pebble soil, large stone soil |
| | V | Soft rock, rock fragmentation; soft rock, rock mass is broken ∼ broken; extremely broken all kinds of rock mass. Broken, cracked, loose structure | ≤250 | | Generally, quaternary semidry clay to hard plastic clay and slightly wet to wet gravel soil, pebble soil, gravel, brecciated soil and loess (Q3, Q4). Noncohesive soil has loose structure, clay soil and loess have soft structure |
| | VI | Soft plastic clay and wet, saturated fine sand layer, soft soil, etc. | |
|
|
