Overburden Failure Research Articles

In situ investigations into mining-induced overburden failures in close multiple-seam longwall mining: A case study

Preventing water seepage and inrush into mines where close multiple-seam longwall mining is practiced is a challenging issue in the coal-rich Ordos region, China. To better protect surface (or ground) water and safely extract coal from seams beneath an aquifer, it is necessary to determine the height of the mining-induced fractured zone in the overburden strata. In situ investigations were carried out in panels 20107 (seam No. 2-2upper) and 20307 (seam No. 2-2middle) in the Gaojialiang colliery, Shendong Coalfield, China. Longwall mining-induced strata movement and overburden failure were monitored in boreholes using digital panoramic imaging and a deep hole multi-position extensometer. Our results indicate that after mining of the 20107 working face, the overburden of the failure zone can be divided into seven rock groups. The first group lies above the immediate roof (12.9 m above the top of the coal seam), and falls into the gob after the mining. The strata of the second group to the fifth group form the fractured zone (12.9-102.04 m above the coal seam) and the continuous deformation zone extends from the fifth group to the ground surface. After mining Panel 20307, a gap forms between the fifth rock group and the continuous deformation zone, widening rapidly. Then, the lower portion of the continuous deformation zone cracks and collapses into the fractured zone, extending the height of the failure zone to 87.1 m. Based on field data, a statistical formula for predicting the maximum height of overburden failure induced by close multiple seam mining is presented.

Visual Exploration of the Spatiotemporal Evolution Law of Overburden Failure and Mining-Induced Fractures: A Case Study of the Wangjialing Coal Mine in China

The borehole television approach is an effective way of detecting mining-induced fractures in overburden strata as it can visualize fractures to facilitate a quantitative analysis of size, quantity, length, and other features. In this article, the borehole television approach is applied on panel 20105 of the Wangjialing Coal Mine in China to investigate the overburden movement and spatiotemporal evolution law of mining-induced fractures from the coal seam to ground surface. The results revealed that the overburden strata experienced the phases of roof caving, generation of fracture, bed separation, dislocations, fracture propagation, surface subsidence, and closing of fractures. The process can be divided into the initiation stage, the active stage, and the degradation stage along the mining direction. For exploited working faces, the caved zone height is 2.9–4.11 times the mining height, and the height of the fractured zone is 19.35–22.19 times the mining height. The height range of the three parts in the fractured zone is 24–26, 40–45, and 30–35 m. Significant fractures were observed in the bending zone. Step subsidence and cracks, which indicate severe damages, were observed on the ground surface above the goaf.

Environmental implications of mitigating overburden failure and subsidences using paste-like backfill mining: a case study

This paper presents an investigation on the effectiveness of mitigating overburden failure and subsidences using a paste-like backfill method for coal mining. The Taiping Coal mine is the first Chinese coal mine which has adopted a paste-like backfill mining method to mitigate overburden failure and minimise subsidences. Overburden failure induced by longwall caving and backfill mining has been comparatively studied by in situ measurements, an empirical formula, a scale model and numerical simulations for a case study in the Taiping Coal mine. The results show that the heights of the caving and water flow fracture zones, and the range and value of the subsidences due to backfill mining are quite smaller than those resultant of longwall caving mining. The mining operations in the Taiping Coal mine have proven the reliability of this backfill mining method to mitigate overburden failure and subsidences so as to prevent coalmines from water and sand inrushes and protect farm land and surface buildings.

Study on the Monitoring Method of Overburden Failure of Shallow Wongawilli Mining Working Face

Through the practice and improvement of Wongawilli Mining method in Shendong Mining Area, it created Shendong Characteristic short wall mechanize room mining method. Due to the shallow coal seam, the fracture zones throughout the bedrock directly after the mining, therefore the bending sinking belt didn’t exist; the conventional "three zones" theory couldn’t explain the overburden rock deformation damage rule of this situation perfectly. In order to monitor the damage of overburden strata, based on the analysis of coal pillars stability in Wongawilli working face, the paper puts forward 3D monitoring methods of overburden strata damage as follows: underground borehole stress monitoring, roof separated strata and layer's internal monitoring, surface subsidence monitoring. The set of monitoring method can monitor the instability of coal pillars, roof caving, production of separated strata in the roof, overburden rock damage and subsidence, the study is of reference and significance.

Integrated Simulation Test for Distortion and Failure of the Top Rock by Seismic Wave CT and Resistivity Method in Mining Workface Model

The height of “two belts” for overburden distortion and failure in mining workface is very important to coal mine safety production. The height results can be gained through mine geophysical method. The geological model of 32 coal seam in 33 mining field of one mine in Huaibei is selected in the article. The model system of coal mining is formed through the technique of the indoor similar simulation, and the union test system of the bore-laneway resistivity method and seismic wave CT method is found. Through simulating mining process of workface, the distribution of the resistivity and wave velocity in the top rock of detecting field is tested and analyzed. The understanding of development regularity for the distortion and failure of top rock during mining of coal seam is obtained, and it can provide correct guidance parameters for practical production in mine. The results of integrated simulation show that the bore-laneway detecting system can give clear resistivity reaction of distortion and failure, and the seismic wave CT method can provide complete velocity distribution of rock development. The integrated system has high resolution for distortion of the top rock, and can give correct height of “two belts”. The simulating achievement is coincided with the practical detection in mine, and it is helpful to renewal and develops the theory and practice of testing technique of overburden failure in mine.

Aquifer protection during longwall mining of shallow coal seams: A case study in the Shendong Coalfield of China

Large-scale underground mining of shallow coal seams can have significant impacts on ground surface and potentially leads to incidental damage to the overlying aquifer with subsequent environmental hazards. In order to deal with the apparent conflict between water protection and high production in underground mining, an aquifer protection mining technique was trialed in panel #51201 in the Shangwan colliery, the Shendong Coalfield, China. Overburden failure, water level of the unconsolidated aquifer, surface cracks, and ground subsidence were monitored in a series of boreholes using borescope, and also by observations in a nearby water well and by surface surveys. Monitoring results indicate that the aquifer protection mining technique can be successfully applied by modifying a few mining parameters such as mining height or advance rate under some suitable geological conditions. The critical zone in the stratigraphy appears to be the weathered bedrock located immediately below the aquifer. The weathered bedrock will remain impermeable after mining as long as its thickness is greater than the mining height. The development of the mining-induced overburden failure is affected by the key strata but ultimately controlled by the soft aquiclude such as the weathered zone. It was observed respectively that the height of the caved zone was observed to be 5 to 6 times the mining height, whilst the height of the fractured zone is about 10 to 11 times the mining height.

Model test of the overburden deformation and failure law in close distance multi-seam mining

Based on characteristic of the associated mining of multi-coal seam and the engineering geological characteristics of overburden, the mining impact pattern of multiseam mining and the dynamic fracture mechanism of overburden were characterized by applying the engineering geological mechanical model test. The related strata movement parameters and influence area of multi-seam mining were obtained. the strike boundary angle is 61°, the full extraction coefficient is 0.93, the greatest subsidence angle is 81°, the horizontal movement factor is 0.38, the deviation of inflection point /mining deep is 0.11. The development height of caving zone and water flowing fractured zone of multi-seam mining were calculated, is 32 m and 81.5 m separatly. The assess of influence degree of coal layer safety mining is that, there exists the possibility of water and sand inflow when mining, some messures for mine water prevention and control should be used, and the mining thickness should be local strictly limit.

Experimental Research on Resistivity Response Characteristics to Overburden Deformation and Failure

AbstractThe survey of the overburden deformation and failure caused by underground mining may provide reliable guidance for mining design and safe production. This paper deals with the similarity conditions and the practicability of model experiment, makes the dynamic survey of the electric field characteristics changes of overburden at different mining stages, makes inversion with the experiment data and uncovers the response characteristics of resistivity changes with overburden deformation and failure. The experiment results indicate that the overburden deformation and failure cause the electric characteristics changes of rock strata, the response characteristics of resistivity changes vary with the failure degrees in different failure zones, and they are corresponding.