Field Industrial Test Research Articles

Impact of hydraulic fracturing and borehole spacing on gas drainage along a coal seam

Hydraulic fracturing is a technology employed to improve coal seam permeability and gas drainage. This study uses theoretical analysis and field testing to examine the mechanisms of hydraulic fracturing of a coal seam, including the initiation conditions of boreholes and cracks, main crack forms, and expansion and extension processes. RFPA2D-flow software was used to develop a numerical simulation of double-hole hydraulic fracturing, from crack initiation to expansion and extension in the coal body. The numerical simulation revealed characteristics and evolution of the stresses, water pressure and acoustic emission around the boreholes and estimated the permeability improvement range of fracturing holes under conditions of different hole spacing. Results of a field industrial test showed that the daily gas drainage pure flows increased by 5.8-17.6 times, the average gas drainage velocity reached 3.76 m3/min (maximum 10 m3/min), the gas drainage rate of the working face reached 57.32%, and the influence radius of single-hole hydraulic fracturing is approximately 5 m. This study demonstrates that hydraulic fracturing and permeability improvement technology can greatly improve the gas drainage rate of boreholes in a coal seam.

Safety Mining Technology of Coal Seams in Weathered Zone Based on Ground J-Type Pregrouting Reinforcement

A thin basement coal seam mining model under different overlying strata conditions was developed using the discrete element software UDEC. This approach is used to discuss the safety mining of the thin basement coal seams. Fracture development in overlying and rock strata movement law in the stope was discussed. The relationship between support and surrounding rocks under different overlying strata conditions was analyzed. Lastly, a field industrial test was conducted based on the research results. A few major conclusions could be drawn. Under load transmission in loose water-bearing strata, causing a large-scaled rock strata movement to advance into the working face is easy when only one bearing stratum exists in the overlying strata. Meanwhile, the support bears strong loads, which can easily be collapsed. When two bearing strata exist in the overlying one, the upper bearing stratum can form a voussoir beam structure. Loads on the support decreased substantially compared with those under single bearing stratum, whilst the probability of pressing frame was reduced accordingly. A weathered zone above the stope was reinforced by ground J-type drilling pregrouting, thereby improving the physical and mechanical properties and increasing the bearing capacity of the rock strata in the grouting range and safety mining of the working face in the lower coal seams. Research results provide important references for the safety mining of thin basement coal seams under similar conditions.

Combined Supporting Technology with Bolt-Grouting and Floor Pressure-Relief for Deep Chamber: An Underground Coal Mine Case Study

Based on the engineering geological conditions of the Number 2 chamber in the slope at Xinzhuang coal mine, which is located in the eastern part of Yongcheng City, Henan Province, China, the authors conducted a systematic research on the anchoring-grouting and the floor pressure-relief supporting technology by using theoretical analysis, numerical calculation and field industrial test. Results showed that: (1) the lithology of the surrounding rock was poor, and the stress and effective loading coefficient on the chamber surrounding rock were high due to the abutment pressure that was induced by the shaft protective pillar. Both of them resulted in the floor heave and the surrounding rock deformation damage of the chamber; (2) The numerical calculation showed that, after the floor pressure-relief slot was excavated in the head chamber, the vertical stress of the floor surrounding rock of chamber and the horizontal stress of the side surrounding rock were significantly reduced when compared with the stress before the pressure-relief, and the floor vertical displacement basically remained unchanged. So the floor pressure-relief slot could effectively control the chamber floor heave and was helpful for the long-term stability of the chamber. After the severe deformation chamber was renovated by using a combined support with bolt-mesh-shotcreting and anchor cables, several other techniques were also applied to ensure the stability of the chamber. The floor pressure-relief slot was excavated, both the roof and the sides surrounding rock of chamber were grouted with grouting bolt, and both sides and the floor (including pressure-relief slot) of the chamber were grouted with anchor cable bundles. After implementation of above systematic techniques, the surrounding rock of chamber is in a stable state, which demonstrated that the field test is successful. The combined supporting technology with the anchoring-grouting and the floor pressure-relief has an important practical significance for the long-term stability of the chamber to ensure the safe and efficient production of the mine.

Research on Deformation Mechanism of Retracement Channel during Fully Mechanized Caving Mining in Superhigh Seam

The multichannel retracement in the auxiliary laneway has become one of the key technologies in the high‐yield and high‐efficiency production of large and extra‐large coal mines in western China. For the successful application of this technology, the control of retracement channel deformation is decisive. This paper takes the support of the retracement channel in full‐mechanized caving working surface of Mentai Buliangou Coal Mine as the engineering background. In view of the occurrence characteristics of thin bedrock, thick unconsolidated layer and superhigh seam, theoretical analysis, numerical calculation, and field industrial test are adopted. The deformation rules and stress distribution characteristics of the surrounding rock as well as the changes of the support structure in the retracement channel during the end mining on the full‐mechanized caving working surface are systematically studied, and the deformation and failure mechanism of the surrounding rock is revealed. The field measurement shows that the adoption of optimal design scheme can effectively control the deformation of the surrounding rock in the retracement channel during the end mining period and consequently address the problem of rapid moving of the working surface, which is significant for engineering practices.

Cable-truss supporting system for gob-side entry driving in deep mine and its application

In order to solve the large deformation controlling problem for surrounding rock of gob-side entry driving under common cable anchor support in deep mine, site survey, physical modeling experiment, numerical simulation and field measurement were synthetically used to analyze the deformation and failure characteristics of surrounding rock. Besides, applicability analysis, prestress field distribution characteristics of surrounding rock and the control effect on large deformation of surrounding rock were also further studied for the gob-side entry driving in deep mine using the cable-truss supporting system. The results show that, first, compared with no support and traditional bolt anchor support, roof cable-truss system can effectively restrain the initiation and propagation of tensile cracks in the roof surrounding rock and arc shear cracks in the two sides, moreover, the broken development of surrounding rock, roof separation and extrusion deformation between the two sides of the roadway are all controlled; second, a prestressed belt of trapezoidal shape is generated in the surrounding rock by the cable-truss supporting system, and the prestress field range is wide. Especially, the prestress concentration belt in the shallow surrounding rock can greatly improve the anchoring strength and deformation resisting capability of the rock stratum; third, an optimized support system of “roof and side anchor net beam, roof cable-truss supporting system and anchor cable of the narrow coal pillar” was put forward, and the support optimization design and field industrial test were conducted for the gob-side entry driving of the working face 5302 in Tangkou Mine, from which a good supporting effect was obtained.

厚煤层综放开采沿空留巷技术研究

为提高厚煤层开采煤炭资源回收率，减少巷道掘进量，本文以晋煤集团某矿4311综放工作面为工程背景，通过充填体支护阻力计算得出合理充填体宽度为2 m，据此确定了充填材料的最佳水灰比，并提出了巷旁充填施工工艺。现场工业性试验表明，该技术条件下的沿空留巷巷道维护效果良好，能较好地满足煤矿安全生产要求。 In order to improve the recovery rate of coal resource in thick coal seam mining and reduce the amount of roadway driving, in this paper, under the engineering background of the 4311 fully mechanized coal mining group of a mine, Shanxi Coal Group, through the calculation of the filling body, the reasonable filling width was 2 m, the optimal water cement ratio of the filling material was determined, and then the construction technology of the filling of roadside packing was put forward. Field industrial test shows, under the condition of the technology, that the maintenance effect of the roadway of gob side entry retaining is good. Therefore, it can achieve the coal mine safety production requirements better.

Parameter Design and Application of Hydraulic Support with Hanging Chain and Splicing Beam in Shallow Seams

In view of actual situation of serious resources waste and less than 30% of face recovery ratio to shallow seams with existing features of harder roof at the process of room and pillar mining in northern Shaanxi province in China, reasonable support strength has been studied in both cases of normal mining and force caving for improved longwall mechanized mining face, and obtained reasonable working support resistance at the condition of force caving which was better than normal mining. Based on this condition, Shandong Xin Mei machinery Co, Ltd. has developed hydraulic support with hanging chain and splicing beam which was suitable to existing features of shallow seams. The support had advantages with flexible connection between supports to ensure that all pillars reached rated setting load, sub-size top beam to resolve "protection" and "cutting" dilemma for the roof, adjusting and locking support, etc. The company also has given concrete support parameters. By the field industrial test verification, the developed new support fully adapted strata behavior at the process of force caving with existing features of shallow depth and harder roof. The research has provided a useful reference for other coal mines with similar geological features.