Table 1.

Degradation classification of karst tiankengs.

Item	Light degradation	Moderate degradation	Severe degradation	Heavy degradation
Depth-width rate	(0.45, 1]	(0.35, 0.45]	(0.1, 0.35]	(0, 0.1]
Damage degree of wall area	0–20%	21–50%	51–80%	> 81%
Quantity of rocky slope	< 1	1–2	3	> 4 (Circularity distribution)
Trapping	Good trapping	General trapping	Slightly poor trapping	Poor trapping
Pattern of pithead	Approximately ellipse	Irregular ellipse	Irregular polygon	Approximately large doline