DEA models with Russell measures

In real applications, data envelopment analysis (DEA) models with Russell measures are widely used although their theoretical studies are scattered over the literature. They often have seemingly similar structures but play very different roles in performance evaluation. In this work, we systematically examine some of the models from the viewpoint of preferences used in their Production Possibility Sets (PPS). We identify their key differences through the convexity and free-disposability of their PPS. We believe that this study will provide guidelines for the correct use of these models. Two empirical cases are used to compare their differences

Paleocollapse structure as a passageway for groundwater flow and contaminant transport

Paleocollapse structure is a rock collapse, resulting from the failure in the geological history of the bedrock overlying karstified limestone. Depending on the present hydrogeological conditions within the area of paleocollapse and the internal properties of these structures, they can provide a means to facilitate groundwater flow and contaminant transport. Inactive paleocollapse structures can be reactivated by human activities such as dam construction, mining underground minerals, pumping groundwater, and development of landfills. They can also be reactivated by natural events such as earthquakes and neotectonic movements. In the mines of northern China, sudden inflow of karst water from Ordovician limestone into drifts and mining stopes through paleocollapse structures has caused significant economic loss. Water pumping tests and accompanied dye traces are effective approaches of locating water-conducting paleocollapse structures. Grouting is probably the best means of preventing them from becoming geohazards

The formation of sinkholes in karst mining areas in China and some methods of prevention

Mining of coal, lead and zinc, gold, and iron ore deposits in karst areas has been closely associated with sinkholes in China. Surface collapse causes an increase in mine water drainage and the possibility of major water inflow from karst aquifers, which threatens the environment in mining areas and endangers mine safety. The origin of such sinkholes is analyzed quantitatively in this paper and a combination of factors including soil weight, buoyancy, suffosion process and vacuum suction can contribute to surface subsidence. The key measures to prevent sinkholes in mining areas are to control the amount of mine drainage, reduce water-level fluctuation, seal off karst conduits and subsurface cavities in the overlying soil, prevent water inflow, and to increase gas pressure in the karst conduits

Karst Paleo-Collapses and Their Impacts on Mining and the Environment in Northern China

Karst paleo-collapses are unique collapse structures widely found in the coal measures of northern China. Their geometric dimensions and internal properties indicate that a compound dissolution of carbonate and gypsum rocks may contribute to their formation. When these collapses are permeable to groundwater flow, they hydraulically connect the coal seams and the karst aquifers, which is a pre-requisite for water inrushes during coal mining. Over the last 40 years, water inrushes through these collapses have caused fatalities, economic losses, and degradation in the environment in northern China. Determination of locations and hydrogeological characteristics of the karst paleo-collapses are essential in preventing water inrush incidents through them. Advanced geophysical prospecting, aquifer testing and accompanied dye tracing are effective approaches to investigating these structures

Karst Paleo-Collapses and Their Impacts on Mining and the Environment in Northern China

Karst paleo-collapses are unique collapse structures widely found in the coal measures of northern China. Their geometric dimensions and internal properties indicate that a compound dissolution of carbonate and gypsum rocks may contribute to their formation. When these collapses are permeable to groundwater flow, they hydraulically connect the coal seams and the karst aquifers, which is a pre-requisite for water inrushes during coal mining. Over the last 40 years, water inrushes through these collapses have caused fatalities, economic losses, and degradation in the environment in northern China. Determination of locations and hydrogeological characteristics of the karst paleo-collapses are essential in preventing water inrush incidents through them. Advanced geophysical prospecting, aquifer testing and accompanied dye tracing are effective approaches to investigating these structures

Engineering Issues on Karst

The design and construction of engineering structures in karst regions must deal with such challenges as difficulty in excavating and grading the ground over pinnacled rockheads, instability of ground surface, and unpredictable groundwater flow conditions. Detailed subsurface investigation using boring exploration, geophysical techniques, tracer testing, and groundwater monitoring helps optimize foundation designs and minimize uncertainties inherent in their construction. Based on the maturity of karst landscapes, depth and dimension of karst features, and vulnerability of groundwater contamination, methods that have been established to control surface water and groundwater and minimize sinkhole development include relocating structures to a safer site, filling voids/fractures with concrete, soil reinforcement, constructing deep foundations, and remediating sinkholes

Comprehensive Investigation and Remediation of Concealed Karst Collapse Columns in Renlou Coal Mine, China

Coal mining in China has exposed numerous karst collapse columns of tens of meters in diameter and hundreds of meters in height. Hydraulically conductive collapses have functioned as groundwater pathways between the underground workings and the aquifers, resulting in water inrushes during coal mining. Over the last 40 years, water inrushes through these collapses have caused fatalities, economic losses, and degradation in the environment. Two such collapse features were unexpectedly encountered during operations in Renlou Coal Mine of China. The first encounter caused flooding of the entire mine. Although no serious damages occurred at the second encounter, because of timely and effective grouting measures, the production rate was reduced. Proactive detection of any concealed karst collapses and determination of their hydrogeological characteristics were essential components of a comprehensive investigation program in preventing water inrush incidents and ensuring normal coal production in the mine. The investigation program included surface and underground geophysical surveys with five geophysical techniques and directional drilling of three exploratory boreholes at completion depths ranging from 902 to 986 m. A new collapse feature was identified through systematic analysis of the data collected in the investigation program. Although the bottom of the collapse feature has not been determined, its total height is more than 135 m. The roof was at approximately 785 m depth, and there was an open void 1.5 - 2 m high at the top. Geotechnical properties, results from packer testing and tracer testing, monitoring of potentiometric pressures, and geochemical fingerprinting suggested that this collapse column was hydraulically conductive and still actively developing. Water in the confined thin-bedded limestone and Ordovician limestone aquifer that either overlies or underlie coal seams could flow into the mining areas if this feature were not identified in advance but encountered during mining. A grouting program was designed and implemented to construct a water plug in the collapse that effectively cut off the hydraulic connections from the aquifers to underground workings. Successful construction of the water plug in the collapse was confirmed by water intake tests in the grouting holes, water flow measurements in the mining area, and groundwater level monitoring in the aquifer

Comprehensive Investigation and Remediation of Concealed Karst Collapse Columns in Renlou Coal Mine, China

Coal mining in China has exposed numerous karst collapse columns of tens of meters in diameter and hundreds of meters in height. Hydraulically conductive collapses have functioned as groundwater pathways between the underground workings and the aquifers, resulting in water inrushes during coal mining. Over the last 40 years, water inrushes through these collapses have caused fatalities, economic losses, and degradation in the environment. Two such collapse features were unexpectedly encountered during operations in Renlou Coal Mine of China. The first encounter caused flooding of the entire mine. Although no serious damages occurred at the second encounter, because of timely and effective grouting measures, the production rate was reduced. Proactive detection of any concealed karst collapses and determination of their hydrogeological characteristics were essential components of a comprehensive investigation program in preventing water inrush incidents and ensuring normal coal production in the mine. The investigation program included surface and underground geophysical surveys with five geophysical techniques and directional drilling of three exploratory boreholes at completion depths ranging from 902 to 986 m. A new collapse feature was identified through systematic analysis of the data collected in the investigation program. Although the bottom of the collapse feature has not been determined, its total height is more than 135 m. The roof was at approximately 785 m depth, and there was an open void 1.5 - 2 m high at the top. Geotechnical properties, results from packer testing and tracer testing, monitoring of potentiometric pressures, and geochemical fingerprinting suggested that this collapse column was hydraulically conductive and still actively developing. Water in the confined thin-bedded limestone and Ordovician limestone aquifer that either overlies or underlie coal seams could flow into the mining areas if this feature were not identified in advance but encountered during mining. A grouting program was designed and implemented to construct a water plug in the collapse that effectively cut off the hydraulic connections from the aquifers to underground workings. Successful construction of the water plug in the collapse was confirmed by water intake tests in the grouting holes, water flow measurements in the mining area, and groundwater level monitoring in the aquifer