Classifications and characteristics of karst collapse columns in North China coalfields

On the basis of summarizing many water inrush cases of collapse columns in North China coalfields and investigations on over 40 mine areas,Xuhuai coalfield,four developing phases are divided according to the hydrologic and engineering geology characteristics in different developing phases.They are prophase,intensity phase,decline phase and death phase.By analyzing the different strata where collapse columns developed in North China coalfields,three types of strata are classified: the soluble rock group above Ordovician,Ordovician soluble rock group,Cambrian soluble rock group.Consequently,12 types of collapse columns are classified integratedly.And the geologic characteristics of each type of collapse column are analyzed and summarized.