Bao-yu Li

Bio: Bao-yu Li is an academic researcher from China University of Mining and Technology. The author has contributed to research in topics: Cantilever & Port (circuit theory). The author has an hindex of 2, co-authored 3 publications receiving 50 citations.

Pressure relief and structure stability mechanism of hard roof for gob-side entry retaining

Abstract: In order to explore the pressure relief and structure stability mechanism of lateral cantilever structure in the stope under the direct coverage of thick hard roof and its impact on the gob-side entry retaining, a lateral cantilever fractured structural mechanical model was established on the basis of clarification for the stress environment of gob-side entry retaining, and the equation of roof given deformation and the balance judgment for fracture block were obtained. The optimal cantilever length was proposed based on the comparison of roof structural characteristics and the stress, deformation law of surrounding rocks under six different cantilever lengths by numerical simulation method. Double stress peaks exist on the sides of gob-side entry retaining and the entry located in the low stress area. The pressure of gob-side entry retaining can be relieved by reducing the cantilever length. However, due to the impact of arch structure of rock beam, unduly short cantilever would result in insufficient pressure relief and unduly long cantilever would bring larger roof stress which results in intense deformation. Therefore, there is optimal cantilever length, which was 7-8 m in this project that enables to achieve the minimum deformation and the most stabilized rock structure of entry retaining. An engineering case of gob-side entry retaining with the direct coverage of 10 m thick hard limestone roof was put forward, and the measured data verified the reasonability of conclusion.

External port free type convergence instrument and measurement method thereof

Abstract: The invention discloses an external port free type convergence instrument and a measurement method thereof. The external port free type convergence instrument mainly comprises a deep anchoring base rod, multiple sections middle connection rods and an external port free rod, wherein the deep anchoring base rod is in threaded connection with the middle connection rods; the multiple sections of middle connection rods are connected with one another end to end; the number of middle connection rods is determined by the depth of a hole; and the external port free rod is connected to the last middle connection rod at the aperture of the hole. The rod bodies are anchored into a drilled hole after being sequentially connected and fastened; the aperture is wedged by a wedged guide indication disk, and the external port free rod is exposed at a certain length; the reading of a scale on the surface of the external port free rod, which is pointed by the outer edge of the wedged guide indication disk, is read as an initial value and then regularly read; and at the end of observation, the surface convergence amount of an alley during observation is obtained by subtracting the initial reading from the last reading of the scale on the surface of the external free rod. The external port free type convergence instrument has the advantages that structure is simple, use is convenient, accuracy is high, measurement is continuous and can be repeated, the influence on production is little, and the like.

External port free type convergence instrument

Abstract: The utility model relates to an external port free type convergence instrument. The external port free type convergence instrument mainly comprises a deep anchoring base rod, multi-section middle connection rods and an external port free rod, wherein the deep anchoring base rod is in threaded connection with the multi-section middle connection rods, the multi-section middle connection rods are connected with one another end-to-end, the number of the multi-section middle connection rods is determined by depth of a hole, and the external port free rod is connected with the last section of the middle connection rods at a hole port. The rod bodies are anchored into a drilled hole after being sequentially connected and fastened; the hole port is wedged by a wedged guide indication disk, and a certain length of the external port free rod is ensured to be exposed outside; a scale on a surface of the external port free rod which is pointed by an outer edge of the wedged guide indication disk is read as an initial value and then regularly read; and at the end of observation, the surface convergence amount of an alley during observation is obtained by subtracting the initial value from the last value of the scale on the surface of the external free rod. The external port free type convergence instrument has advantages of simple structure, operational convenience, high accuracy, continuous and repeatable measurement, small influence on production, and the like.

Roof Deformation Characteristics and Preventive Techniques Using a Novel Non-Pillar Mining Method of Gob-Side Entry Retaining by Roof Cutting

Abstract: A new non-pillar mining technology, gob-side entry retaining by roof cutting (GERRC), different from the conventional gob-side entry retaining formed by a roadside filling support, is introduced in this study. In the new technology, roof cutting is conducted so that the roof plate forms a short cantilever beam structure within a certain range above the retained entry, thus changing the stress boundary condition of the roof structure. To explore the deformation characteristics of the roof under this special condition, a short cantilever beam mechanical model was established and solved using energy theory and displacement variational methods. Meanwhile, a theoretical and analytical control solution for roof deformation was obtained and verified via field-measured results. Based on the aforementioned calculation, the relationship between the roof deformation and main influence parameters was explored. It was concluded that the rotation of the upper main roof and width of the retained entry had the most significant impacts on roof deformation. Bolt and cable support and temporary support in the entry had a non-obvious influence on the roof deformation and could not prevent the given deformation that was caused by the rotation of the upper main roof. Based on comprehensive theoretical analysis and calculation results, ideas and countermeasures to control short cantilever roof deformation—that is, designing a reasonable height of roof cutting and a controlled width of retaining entry—were proposed and tested. Field monitoring shows that the entry control effects were satisfactory.

Directional hydraulic fracturing to control hard-roof rockburst in coal mines

Abstract: Abstract Hard roof is the main factor that induces rock-burst. In view of the present obvious weakness of control measures for hard roof rockburst in domestic collieries, the mechanism and field application of directional hydraulic fracturing technology for rock-burst prevention have been investigated in this paper using theoretical analysis and numerical simulation. The results show that the weighting span of the main roof and the released kinetic energy as well as the total elastic energy decreased greatly after the directional fracturing of hard roof with the mining progression, thereby reducing the rockburst hazard degree to coal body. The directional hydraulic fracturing technology was carried out in 6305 working face of Jisan Coal Mine to prevent rockburst. Field practices have proved that this technology is much simpler and safer to operate with better prevention effect compared with blasting. By optimizing the operation procedures and developing a new technology of automated high-pressure delivery pipe, the maximum fracturing radius now reaches more than 9 m and the borehole depth exceeds 20 m. Additionally, drilling cutting method was applied to monitor the stress of the coal mass before and after the fracturing, and the drill cuttings dropped significantly which indicates that the burst prevention effect of directional hydraulic fracturing technology is very remarkable. The research results of this paper have laid a theoretical and practical foundation for the widespread application of the directional hydraulic fracturing technology in China.

Floor Heave Mechanism of Gob-Side Entry Retaining with Fully-Mechanized Backfilling Mining

Abstract: 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.