The Appeared Rule of Mine Pressure Observation of Gob-side Entry Retaining in Thin Coal Seam
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In the process of gob-side entry retaining implementation,in order to observe the surrounding rock activity law of two crossheading of gob-side entry retaining in the working face and during the secondary mining influence period,observe the deformation of roadway surrounding rock of roadway and obturator etc,we set the corresponding station in the process of gob-side entry retaining to observe the surface displacement and deep displacement of surrounding rock,and the stress variation of surrounding rock etc,in order to verify the effect of the gob-side entry retaining.Cite
Gob-side entry retaining, also termed as non-pillar mining, plays an important role in saving coal resources, high production and efficiency, extending the service life of mine and improving the investment benefit. Herein, a gob-side entry retaining method involving the use of bag filling material for wall construction is proposed based on the thin seam mining characteristics. First, a gob-side entry retaining mechanical model is established, and the side support resistance of the 8101 working face is calculated. The mechanical properties of the bag material are investigated through experiments, and the construction technology of the gob-side entry retaining approach involving the use of bag filling material for wall construction is introduced. The deformation on the two sides, the roof and floor of the roadway, are simulated via numerical methods and monitored during field tests. The results show a small control range for the deformations and a good roadway retention effect, thereby proving the feasibility of the bag filling material for wall construction. This study provides a reference for the development of gob-side entry retaining mining for thin coal seams.
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To solve the control problem of the surrounding rock of gob-side entry retaining under typical roof conditions in deep mines, we conduct theoretical analysis, numerical simulation, and actual measurements. Starting from the plastic zone of the surrounding rock, the serious damage area, the degree and scope of damage, and the dynamic evolution process of the surrounding rock of the gob-side entry retaining are systematically analyzed under four typical roof conditions in deep mines; the expansion and evolution laws of the plastic zone of the surrounding rock are expounded; and a key control technology is proposed. The results indicate that (1) the plastic failure of surrounding rock was concentrated mainly on the coal side and on the floor, especially in the filling body. The plastic zone of the surrounding rock of the gob-side entry retaining with the thick immediate roof was widely distributed and deep, but the plastic failure of the filling body was not obvious. The plastic failure of the surrounding rock of the gob-side entry retaining with the compound roof was mainly concentrated on the roof, filling body, and floor of the filling area. (2) According to the typical roof conditions of the deep gob-side entry retaining, the order of the degree of damage to the surrounding rock was as follows: thick immediate roof, compound roof, thin immediate roof, and thick-hard roof. (3) A “multisupport structure” control system is proposed for the gob-side entry retaining in a deep mine, including measures for enhancing the bearing performance of the anchorage system, increasing the strength of the cataclastic coal-rock mass, enhancing the bearing capacity of the filling body, and increasing the bearing capacity on the tunnel side. The proposed technology was applied to the deep gob-side entry retaining project in the east area of Panyi Mine, and it effectively fulfilled the reuse requirements of gob-side entry retaining in deep mines.
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On the bases of theoretic analysis, numerical simulation, and project practice, stress distribution of surrounding rock and movement characteristics of roof strata in T-junction area of gob-side entry were analyzed. Besides, control technology in T-junction area was proposed after indicating deformation characteristics of different stages in gob-side entry. Results show that there is an inclined block in T-junction area after fracture of main roof and the period when the block is tending to stability is a critical stage of pressure appearance for gob-side entry. Further, three stress zones: in-situ stress zone, abutment pressure zone and low stress zone appear in both strike and dip of mining panel and enhanced support of gob-side entry before excavation should keep away from the abutment pressure zone, which also indicates that deep bolting support can exert the bearing capacity of deep rock mass. Additionally, the whole procedure of surrounding rock deformation can be divided into four stages and deformation in gob-side entry is larger than that of entry excavation, which means that efficient support design should be taken into account. Ultimately, district control technologies for surrounding rock of gob-side entry in back zone, filling zone, and front zone are proposed and it showed a good adaption in project practice of coalmine.
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The transportation roadway of a coalmine's 2408 work face in Hebei province, is selected as the engineering background. And the law of deformation and failure, in the case of gob side entry retaining without coal pillar, have been analyzed. The control mechanism of gob side entry retaining without coal pillar are as follows. The differences between the deformation law of the general conditions and that of strengthen supporting roadway wall are drew with combination of geological production conditions and the using of a numerical simulation software-FLAC3 D. The amount of rock deformation and the area of plastic zone can be greatly reduced by the high strength and preload anchor in roadway wall. The observations mine pressure indicates that, after the secondary effects of mining, the relative maximal roof-to-floor convergence is 471 mm, both sides relative maximal convergence is 315 mm.
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Gob-side entry retaining (GER) is a hot issue with regard to saving resources and reducing the drivage ratio in longwall mining. This paper investigates an innovative approach of roof presplitting for gob-side entry retaining (RPGER). RPGER uses the directional cumulative blasting to split the roof in advance. The rock roof within the presplitting range caves in gob after mining. The caved gangue can become the natural rib of the gob-side entry and expands to be the natural supporting body for resisting the upper roof movement. A numerical model of RPGER was established by the discrete element method (DEM), which showed that the supporting effect by the expanded gangue was well functioning. The gob-side entry was in pressure-relief surroundings and featured in the lesser deformation. The roof presplitting design method was presented and validated with a field test. The test illustrated that RPGER reduced the mining pressure on the retained entry side. The expanded gangue on the entry side was gradually compacted. It is the compaction process that played the role of reliving mining pressure, and the compacted gangue became the effective rib of the gob-side entry. The retained entry in the pressure-relief surroundings would stabilize a lagging distance behind the working face. The gob-side entry after stabilization met the entry retaining and the safety production requirements. This work illustrates the mechanism of RPGER and validates its feasibility and efficiency.
Gangue
Crusher
Longwall mining
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Gob‐side entry retaining is an environmentally friendly nonpillar mining technology with high efficiency and safety. With the continuous exploration of the gob‐side entry retained by filling (GERF) with roadside supports, the GERF has enabled nonpillar mining. However, dense roadside supports or filled artificial pillars become subject to the pressure of roof pressure instead of coal pillars, which causes problems. Recently, an original innovative gob‐side entry retaining technology by roof cutting and pressure relief (RCPR) was developed and extensively implemented in China’s coal production. The gob‐side entry formed by different retaining methods has exhibited some differences in the strata behaviors and the results of retained roadways. Via industrial case and numerical simulation, this study explored the influence of entry retaining methods on the results of the entry retained. The results indicate that the total deformation of the surrounding rock of the GERF is larger and more severe; the convergence between the roof and floor and the entry sides displacement is 885 mm and 216 mm, respectively; the hydraulic support pressure near the retained entry is larger; and the peak value is 38.7 MPa. The deformation of the surrounding rock by RCPR is relatively small; the convergence between the roof and the floor and the entry sides displacement is 351 mm and 166 mm, respectively; the hydraulic support pressure near the retained entry is weakened to a certain extent; the peak value is 32.2 MPa; and the peak pressure is reduced by 16.8% compared with the GERF. A numerical simulation analysis reveals the following findings: RCPR changes the surrounding rock structure of a gob‐side entry, optimizes the surrounding rock stress environment, and belongs to active pressure‐relief entry retaining; the GERF does not adjust the surrounding rock structure of a gob‐side entry and belongs to passive pressure‐resistance entry retaining; and the surrounding rock of a gob‐side entry is significantly affected by pressure. These two methods of gob‐side entry retaining have different effects on the surrounding rock of the entry retained. This study can contribute to an exploration of the strata behaviors and the results of a retained roadway by the GERF or RCPR method.
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Aimed at an effective support of the gateway roof and control of the surrounding rock,this paper,based on the control mechanism of the gob-side entry retaining wall rock,introduces the application of the filling process and system designed for gob-side entry retaining with fly ash-high water filling materials and field test of roadside packing in gob-side entry retaining in the third working face in Xin'an coal mine,located in Shuangyashan. The results show that gob-side entry retaining is accompanied by an increase in roadway roof and floor due to the increasing distance of mining face; the filling bodies,capable of positive roof contact and an effective prevention of the deformation of the main roof,tend to be stronger due to increasing time; and filling strips of the better compactness are capable of preventing the harmful gas from escaping. The study serves as reference for the mine gob-side entry retaining in the mines of the similar conditions.
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Taking working face gob-side entry retaining as an example,analyzed the roadway superficial displacement in the front and the rear of the woking face,discussed the supporting body′s load bearing and distortion rule after gob-side entry retaining,studied the rockbolt load in the drift.The result indicates that the roof,two sides of drift and supporting body are stable before gob-side entry retaining and during the period of mining.This conclusion has the guide sense to promoting the technology of gob-side entry retaining.
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