Local dynamic balance theory and technology of flow field in multilayer gob area

Flow field in multilayer gob area, which formed in small hiden-depth, multi-coal layer groups, close distance, hard coal layer, and hard roof, possesses characteristics such as complex, changeable and unstable. Dynamic balance theory of local flow field in multilayer gob area was built based on the realistic requirement that the serious threat on current mining coal layer by large-scale spontaneous combustion fire on close spontaneous combustion coal layer group of Datong Coal mining area at the ＇di-hard＇ conditions was caused by small coal pit mining. The kernel was in dynamic balance between flow field pressures of working face and local flow field in multilayer gob area was kept by transformation. Corresponding technology and set of devices were developed.

Flow characteristics of three-phase foam in mine gob and its application

To study the flow characteristics of three-phase foam in gob area,different perfusion experiments in coal mine gob were designed and put forward in the paper.Through the observation of flow range,flow characteristics of three phase foam were analyzed with different flow rates.And,unsteady seepage process of three-phase foam was simulated with CFD software.Base on experiment and numerical simulation results,flow characteristics of three-phase foam and its major influence factors are discussed,and the optimal arrangement distribution of mine fire control drills is also determined.Research results show that the flow range and stacking height of three-phase foam in gob are significantly influenced by gravity.The vertical stacking height and horizontal diffusion distance of three-phase foam are also directly related to the flow volume of foam perfusion,the larger flow single hole perfusion volume,the higher stacking height and the longer diffusion distance could be obtained.

Technology of fiber-optic temperature sensing and its application in ＆ temperature measuring of gob area

Based on advantages of technology of distributive fiber-optic temperature sensing and specific to its applications in monitoring mine conflagration, the corresponding Processes such as connection arrangement, signal transmission and monitoring were illustrated. As applied in Sitai Coal Mine of Datong Coal Mine Group Co., this method is effective and accurate and could provide reliable gist for monitoring spontaneous combustion in gob area of mines.

Application of crosswell seismic technique in detecting the gob area of coal mines

To date, significant exploitations of the coal mines have left a considerable number of undetermined empty spaces, also known as the gob areas, behind. The existence of these areas could make the overlaying terrane lose the gravity support. The inhomogeneous sinkage of the overlaying terrane could destroy the buildings constructed on it dramatically, which has currently been a classical geological disaster. In the current study, the crosswell seismic mechanism was addressed and applied to detect the gob area distribution and, espcially, to measure the compaction extent of the gob areas. The results clearly show that the crosswell seismic technique is a very powerful method to discover the distribution and compation degree of the gob areas. More importantly, the current findings provided a novel way for evaluating the compaction extent of the gob areas.

Evaluation of coal pillar loads during longwall extraction using the numerical method and its application

It is very difficult to reasonably evaluate the loads acting on coal pillars in longwall panels during the planning of a new pillar system. The application of empirical equations is a common practice in calculating coal pillar loads while designing a new pillar. This paper proposes numerical models for evaluating coal pillar loads. The key of building a successful numerical model for calculating coal pillar loads lies in the fact that the model should represent the redistribution of stress all over the longwall panels and the surrounding areas, and it is especially important to include the characteristics of the stress rebuilding process in the gob areas, which are crucial for the building process of coal pillar loads. Based on the geo-mechanical background of the Baoshan Coal Mine, this paper details the procedures of applying numerical models to the evaluation of coal pillar loads and their local practices. The study results show it is feasible and reasonable to use numerical models to evaluate coal pillar loads.

Analysis of floor failure depth by using electric profiling method in longwall gangue backfill mining

In underground mining, floor failure depth accompanying mining phases usually results from changes in the advance abutment pressure in the coal mass, and changes in stress redistribution in the areas that have already been mined. Although a variety of techniques have been applied to determine the failure depth, and a number of studies have provided the evidence for the decreasing of failure depth under backfilling, these methods and interactions have not been unequivocally identified. Based on the premise of one possible relation between the failure depth and filling body, which is that the filling materials （gangue） in the gob area can not only restrain the movement of the overlying strata effectively, but also can help to decrease failure depth of the floor in the coal mine. The failure depth in a specific longwall gangue backfilling mine was measured using the mine electricity profiling method. These electrode cables are arranged in a crossheading order to measure the depth and position of the destroyed floor using the DC method. After this, several different methods were used to interpret the recorded data from the field study for gaining failure depth, and the results were compared to the theoretical calculation values. And finally, the authors analyzed the reasons for failure depth form values recorded not indicating a large decrease trend when compared to the theoretical calculation. In this area, it is found that： ① The results using the mine electricity profiling method turns out to be robust and can be used in predicting floor failure depth, and the horizontal position of the maximum destroyed in working face of longwall backfilling. The maximum destroyed position and failure space of the floor can be identified by using this method. ②There is a time-delay processing between the advance of the working face and the failure of floor strata in the mining processing. ③Additionally, based on the data collected from field measurements, which includes three different test electrode spacing approaches （single, double and triple electrode spacing）, and the theoretical value from theoretical calculations. The premise mentioned above cannot be supported during the specific field test, and the role of the filling body in the mined area cannot decrease the floor failure depth effectively in comparison to the theory predictions. Basically, the failure depths in the two different methods have similar results and it is possible that there will not be a direct correlation between the filling body and failure depth. ④Although the failure depth cannot decrease effectiveness when using gangue backfilling in the field testing, due to gob gangue, filling materials being able to deliver the abutment pressure from the overburden in most cases, once they were compacted and rammed by the overburden pressure, it still can make the fracture of the gob area clog and be further consolidated. In this way, it is assumed that water-bursting accidents can be prevented effectively under backfill mining. For this reason, gangue backfilling may make a significant contribution to safety mining.