| Water inrush from karst collapse columns is one of the main types of water disasters in North China's coalfield Water inrush has severe consequences.The different water filling properties of the collapse column directly affect the risk of water inrush on the working face during coal mining and the design of engineering prevention and control measures.Most of the karst collapse columns exposed in Huaibei coalfield are dry or weakly filled with water.However,large water inrush accidents have also occurred from collapse columns,causing huge property losses.The threat of water inrush from karst collapse columns increases with the coalfield entering deep exploration and mining.The structure and hydrogeological conditions of Huaibei coalfield are complicated,and the karst development law,exposure mode,distribution law,and water filling properties of the collapse column vary among different hydrogeological units.Therefore,systematically studying the development characteristics,development patterns,water filling properties,and control mechanism of karst collapse columns in Huaibei coalfield has high theoretical and application values.This study adopted the karst collapse columns in Huaibei coalfield as the research object.Various methods,such as field exploration,field test,laboratory test,and model prediction,were used for a comprehensive investigation of the exposure methods,development rules,and water filling characteristics of the karst collapse columns in Huaibei coalfield.The relationships between karst collapse columns and limestone strata combination,coalfield structural system,geological(hydrogeological)unit,ancient runoff field,current geothermal field,modern runoff field conditions,karst development,and structural evolution were analyzed.Formation models of karst collapse columns were established,the main factors that control the water filling property of karst collapse columns were revealed,and the karst collapse columns of typical formation modes in Huaibei coalfield were predicted.The main achievements are as follows:1)In accordance with the geological structure,the sedimentary characteristics of the bedrock surface and loose layer,and the hydrochemical characteristics of the aquifers,the geology(hydrogeology)unit of Huaibei coalfield was divided into two first-level hydrogeological units and five second-level hydrogeological subunits.Huaibei coalfield is significantly affected by the middle and southern sections of the Xu-Su arc structure,and it has the characteristics of north-south division and east-west segmentation.The Suixiao-Zhahe mining area and the Suxian mining area in the western outer margin or frontal zone of the nappe structure have a relatively large number of exposed karst collapse columns.2)A comprehensive study of the sedimentary combination type,lithological characteristics,limestone composition,and core logging values of the limestone strata in Huaibei coalfield was conducted.The Middle Ordovician limestone strata were determined to be the base strata developed by the karst collapse columns.Furthermore,the karst development characteristics were systematically studied,and the karst development laws of limestone aquifers were clarified.The Middle Ordovician limestone strata have experienced five karst periods,namely,sedimentary,weathering crust,buried,structural(semi-buried),and secondary burial karst periods.The semi-buried karst period is the main period of karst development and karst collapse column formation in Huaibei coalfield.3)The exposed data of the Huaibei coalfield karst collapse columns were systematically sorted and analyzed.A systematic classification of collapsed column characteristics was constructed from the aspects of geometric characteristics,spatial location and distribution law,filling characteristics,and water-filling characteristics combined with the results of geophysical exploration and water release tests.The karst collapse column exposure methods of Huaibei coalfield mainly included three types:direct exposure by mining,water inrush manifestation,and comprehensive judgment.Most of the karst collapse columns were elliptical in-plane and cone in cross-section,and the geometric characteristics were different.The top layer of the column developed from L2 limestone to the loose layer.According to the filling characteristics of the karst collapse column,it can be divided into compacted and uncompacted types.According to the water filling property,it can be divided into non-water,weakly water,and strongly water filling types.The four stages of karst collapse column development were determined.4)On the basis of the study of the structural system,sedimentary characteristics of limestone strata,karst development laws,modern runoff conditions,ancient runoff field recovery,ground temperature distribution laws,karst collapse column development characteristics,and water filling characteristics,six typical formation modes of karst collapse columns in Huaibei coalfield were established.The six types are karst contact zone,syncline structure control,fault structure control,internal circulation control,limestone formation semi-exposed external circulation control,and limestone formation hidden external circulation control types.5)On the basis of the relationship between karst collapse columns and structural characteristics,water abundance of limestone aquifers,hydraulic connection between aquifers,boundary fault properties,supplement and drainage conditions of the minefield,structural evolution of the mining area,water quality and water level abnormalities,and regularity of the ground temperature field,the main control factors for the water filling of three types of collapsed columns were demonstrated.The three types are non-water-filling,column margin weakly water filling,and strong water filling types.Non-water and weakly water filling types involve ancient karst collapse columns,which are the karst results of karstification in Indosinian-Early Yanshanian,Early Yanshanian,and Late Yanshanian.The strong water filling karst collapse columns include the external circulation-controlled development type and the internal circulation-controlled development type,which are the result of modern karstification.Strong water filling karst collapse columns are often exposed in locations with high karst development and strong water-rich aquifers.6)The development characteristics of the karst collapse columns for the inner circulation,outer circulation,and syncline structure control type development modes were quantitatively counted according to the results of the spatial location characteristics and water filling control factors of the karst collapse columns and based on GIS spatial data multi-source information composite technology.The task was aimed at wellfields with typical karst collapse column development patterns.The decision tree classification method and the multi-source information composite prediction method were used to predict the spatial location and water filling of the deep karst collapse column.The accuracy of the karst collapse column development model and the conclusion of the water-filling control mechanism were verified by comparing the prediction results with the actual situation of the exposed karst collapse column.This work expects to provide a spatial target for the prevention and control of deep karst collapse columns.Fig[121 Table[45]Reference[205]... |
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