Control mechanism and technique of floor heave with reinforcing solid coal side and floor corner in gob-side coal entry retaining
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Floor heave is the most common convergence in gob-side entry retaining.The paper analyzes the form,process and characteristics of gob-side entry retaining with the comprehensive methods of theoretical analysis,numerical simulation and the field trial.Research results present that bending and folding floor heave is the main factor in the stage of the first panel mining;squeezing and fluidity floor heave plays a great role in the stable stage of gob-side entry retaining;the combination of the former two factors affects mainly the stage of the second mining ahead;abutment pressure is a fundamental contribution to the serious floor heave of gob-side entry retaining,and sides corners of solid coal body are key part in the case of floor heave controlling of gob-side entry retaining.Floor heave of gob-side entry retaining can be significantly controlled by reinforcing sides and corners of solid coal body,and influence rules on the floor heave of gob side entry retaining of sides supporting strength and the bottom bolt orientation in solid coal side are obtained.Research results have been successfully applied in gob-side entry retaining of G20-F23070 face haulage roadway in #2 coal mine of Pingmei Group,and the field observation shows that the proposed technique is an effective way in controlling the floor heave of gob-side entry retaining.Keywords:
Haulage
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According to the situation of gob-side entry retaining with the large and uneven deformation and poor support effects,took gob-side entry retaining in Qinxin colliery as engineering background,dealt with the numerical simulation analysis the relationship between support inside roadway,surrounding rock deformation and stress distribution,and the obtained support mechanism inside roadway of gob-side entry retaining are as follows:with the application of support with high resistance and yielding,increasing carrying capacity and deformation resistance of surrounding rock in roadway,adapting to large deformation and stress adjustment.The developed support technologies inside roadway of in gob-side entry retaining are:① basic support:using high-strength bolt and anchor support owning high pre-stress force,increasing carrying capacity of surrounding rock and adapting to large deformation;② reinforced support:within a certain range behind working face,in gob-side entry retaining,the hydraulic support with high resistance and yielding is used to strengthen roof and floor support,which means that in the intense stage of roof breakage and stress adjustment of surrounding rock of gob-side entry retaining,the hydraulic support can be used to support the roof and floor effectively and reduce the rotating,sinking of roof and floor heave,maintaining the stability of surrounding rock in gob-side entry retaining;③ after the surrounding rock deformation stability in gob-side entry retaining,the hydraulic support used as reinforced support can be removed.
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Formwork
Abutment
Gangue
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To study the mechanism and control technology of fully mechanized caving gob-side entry driving under the dynamic pressure,S1202 working face of Yuwu Coal Company is taken as objection,a formula for the depth of plastic zone of the roadway floor strata is drawn by analysis the bottom plate force; then the paper analyzes the deformation and failure characteristics of roadway floor under the dynamic pressure.The studies showed that the roadway floor strata were asymmetric deformation,which put forward a reasonable floor heave control technology.
Dynamic pressure
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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.
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Toe
Lateral movement
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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.
Pillar
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Gangue
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Serious floor heave in gob-side entry retaining (GER) with fully-mechanized gangue backfilling mining affects the transportation and ventilation safety of the mine. A theoretical mechanical model for the floor of gob-backfilled GER was established. The effects of the mechanical properties of floor strata, the granular compaction of backfilling area (BFA), the vertical support of roadside support body (RSB), and the stress concentration of the solid coal on the floor heave of the gob-backfilled GER were studied. The results show that the floor heave increases with the increase of the coal seam buried depth, and decreases with the increase of the floor rock elastic modulus. The development depth of the plastic zone decreases with the increase of the c and φ value of the floor rock, and increases with the increase of the stress concentration factor of the solid coal. The development depth of the plastic zone in the test mine reached 2.68 m. The field test and monitoring results indicate that the comprehensive control scheme of adjusting backfilling pressure, deep grouting reinforcement, shallow opening stress relief slots, and surface pouring can effectively control the floor heave. The roof-floor displacement is reduced by 73.8% compared to that with the original support scheme. The roadway section meets the design and application requirements when the deformation stabilizes, demonstrating the rationality of the mechanical model. The research results overcome the technical bottleneck of floor heave control of fully-mechanized backfilling GER, providing a reliable basis for the design of a floor heave control scheme.
Gangue
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