Large Mining Height Research Articles

Stability Analysis and Fracture Patterns of Hard Main Roof in Longwall Top Coal Caving with Large Mining Height

In order to study the fracture patterns of hard main roof in longwall top coal caving (LTCC) with large mining height, a two-dimensional physical similarity model was created to simulate the mining process of No. 8100 large mining height face in Tongxin coal mine, China. The results show that there are three positions of broken line in hard main roof presented with the advance of longwall face, and the underground pressure induced by hard main roof fracturing presents the effect of superposition of large and small periods. It is found that there are two fracture patterns of main roof during the mining process: composite structure of lower cantilever beam and upper voussoir beam with hard main roof and composite structure instability of lower and upper voussoir beam with hard main roof. The underground pressure induced by these two fracture patterns is also analyzed by building mechanical models. In the end, the hydraulic fracture technique is introduced to presplit the main roof and weaken the effect of dynamic loads induced by composite structures instability.

Study on spray dust removal law for cleaner production at fully mechanized mining face with large mining height

Aiming at the problem that it is difficult to control high dust hazard in fully mechanized mining face with large mining height, an airflow-droplet coupled model was established based on the Euler-Lagrange method. Through a custom-developed nozzles atomization experimental system, main parameters were measured, and the built-in butterfly division core nozzle with an aperture of 1.6 mm was selected. The simulation results showed that the range of 1# ~ 3# hydraulic supports on the leeward side of the coal cutter was the best area to prevent dust from spreading to the sidewalk. The spray scheme of four groups of hydraulic supports was used, and each group had six nozzles. The vertical-horizontal combined dispersion scheme and 30° spray scheme were adopted. Besides, the distribution law of average size and concentration of droplets was revealed. After field application, the dust-reduction efficiency of the optimal scheme was 38.3% higher than that of the original scheme.

Study on Dynamic Evolution of Roof Crack and Support Timing of Secondary Tunneling for Large Section Open-Off Cut in Deep Mines

The stability of large section open-off cut in deep mines (LODM) is the key factor affecting the normal equipment installation and safe mining in fully mechanized top-coal caving face. The mechanical model shows that the deflection of the roof of the LODM is proportional to the cubic of span. In this paper, UDEC Trigon model is established, and the parameters of different coal measures strata are modified in detail. The evolution law, failure mode, and damage degree of roof cracks in secondary tunneling are studied, and the roof support effect is analyzed. The numerical simulation results show that the process of roof crack evolution after the primary excavation section and the second excavation section can be divided into three stages according to microseismic activities, and the reasonable supporting time can control the propagation of roof microcracks and reduce the development height of macrocracks. The rock bridge existing in the roof rock stratum after the combined support of long and short anchor cables can effectively limit the formation of macrocracks and their interaction; especially the key support in the interface area can reduce the development height of roof cracks in secondary tunneling and weaken the damage degree of roof rock stratum in the LODM. The field test shows that the moved volume of rib-to-rib and roof-to-floor of the LODM is stable at about 350 mm and 550 mm, respectively. The numerical simulation in this paper is helpful to understand the failure mode of roof in LODM with large mining height and provides a method for the design of its control technologies.

A Mechanical Analysis of Support Instability Risk along the Strike of Coalface in Thick Coal Seam with Large Dip Angle: A Case Study

To ensure safe and high-efficiency mining in the coalface with large dip angle (LDA) and large mining height (LMH), it is important to study the support stability of the coalface under the corresponding conditions. This study is based on the #3up509 coalface of the Gaozhuang Coal Mine (GCM) affiliated with the Zaozhuang Mining Area (ZMA), for which the mechanical characteristics of support in the coalface with LDA and LMH are analyzed. On this basis, the mechanical models for support tilting and sliding in the coalface are developed. Then support stability along the strike of the coalface during the normal mining period (NMP) and special mining period (SMP) is analyzed. The results show that the critical support tilting resistance during the NMP is 52.2 kN, and the critical support sliding resistance is 183.75 kN, and for the SMP, the values are 2679 kN and 4425 kN, respectively. The use of a two-leg shield support, known as ZY6600-25.5/55 (its rated working resistance is 6600 kN), is investigated, which is proved reasonable for the coalface. The influencing factors of support stability along the strike include technical parameters of the support, mining geological conditions of the coalface and specific conditions during mining. Technical measures, such as installing interlock set to fasten support and adjustable lifting jack, increasing the setting load of the support, and optimizing the support displacement method, are taken to increase the overall support stability in the coalface. The initial aim for a safe and high-efficiency mining at the #3up509 coalface has been achieved through the aforementioned measures.

Research on the Influence of the Key Stratum Position on the Support Working Resistance during Large Mining Height Top-Coal Caving Mining

In recent years, in order to increase the coal recovery rate, the large mining height fully mechanized top-coal caving mining has been widely used because it has the advantages of both fully mechanized mining method and large mining height mining method. When this mining technology is used to exploit thick coal seam under upper goaf, the movement characteristics of the overlying strata and the bearing structure formed by the broken rock are complicated, which results in the abnormal pressure during mining, such as severe coal slabs and hydraulic supports being crushed. The key to solve these problems is to study the movement law and the structural evolution characteristics of the overlying strata during large mining height fully mechanized top-coal caving mining, and the movement characteristics of the overlying strata are all determined by the layer-position of the key stratum. UDEC models with different layer-position of the key stratum are established to investigate the influence of the key stratum position on the support working resistance during large mining height top-coal caving mining. Through comprehensive research, the source of support resistance comes from under different geological conditions was analyzed, and the formula for estimating the maximum support working resistance was deduced. In addition, in order to release the severe pressure during large mining height fully mechanized top-coal caving mining, it is recommended to use hydraulic fracturing method to weaken the key stratum in situ.

Analysis of the Protection Performance of Face Guard for Large Mining Height Hydraulic Support

With the increase of mining height, the problem of coal wall spalling in the working face gradually worsens. Hydraulic support and its face guard structure are the key pieces of equipment to restrain the coal wall spalling. However, at present, the hydraulic jack is mostly considered as rigid in the analysis of protection mechanism. This simplification cannot effectively reflect the true bearing state of the face guard. In order to improve the accuracy of analysis, this study considers the face guard jack as a flexible spring and establishes a rigid-flexible coupling analysis model of the face guard mechanism. First, based upon the multibody dynamics software ADAMS®, the multibody numerical model of the face guard of the hydraulic support was established. The influence of the two kinds of structures on the coal wall disturbance was analyzed and compared. Then, the rigid model was meshed. The hydraulic jacks were equivalent to the spring system, and the rigid-flexible coupling model was established. Based upon the application load on different positions of the rigid-flexible model, the load-bearing characteristics and hinge point force transfer characteristics of the two face guards were analyzed. The results show that the support efficiency of the integral type was higher than that of the split type. In the vertical support attitude, the dynamic disturbance of the coal wall, produced by the two kinds of face guards, was small. The four-bar linkage effectively improved the ultimate bearing capacity of the integral face guard. The results provide theoretical support for the design and optimization of the face guard.

Control of Gob-Side Roadway with Large Mining Height in Inclined Thick Coal Seam: A Case Study

The gob-side roadway of 130205, a large-mining-height working face in the Yangchangwan coal mine, was investigated in terms of the mine pressure law and support technology for large mining heights and narrow coal pillars for mining roadways. The research included field investigations, theoretical analysis, numerical simulation, field tests, and other methods. This paper analyzes the form of movement for overlying rock structure in a gob-side entry with a large mining height and summarizes the stress state and deformation failure characteristics of the surrounding rock. The failure mechanism of the surrounding rock of the gob-side roadway and controllable engineering factors causing deformation were analyzed. FLAC3D numerical simulation software was used to explore the influence law of coal pillar width, working face mining height, and mining intensity on the stability of the surrounding rock of the gob-side roadway. Ensuring the integrity of the coal pillar, improving the coordination of the system, and using asymmetric support structures as the core support concept are proposed. A reasonably designed support scheme for the gob-side roadway of the working face for 130205 was conducted, and a desirable engineering effect was obtained through field practice verification.

Analysis of Fracture Mechanics Theory of the First Fracture Mechanism of Main Roof and Support Resistance with Large Mining Height in a Shallow Coal Seam

Because the first-weighting of a main roof with a large mining height has obvious sudden characteristics and is more severe, which causes large-scale support crushing and has a great impact on the ecological environment of the mining area, it is necessary to conduct an in-depth analysis. This paper studies the mechanical mechanism and asymmetric fracture conditions of a main roof with a large mining height, with the first-weighting occurring in a shallow coal seam. In combination with an asymmetric three-hinged arch structural model, the main roof was regarded as a finite plate model with a crack, and a fracture-mechanics model was established. The conditions and main controlling factors of main roof fracture asymmetry were analyzed, and the determination methods of the first-weighting interval and support resistance were further analyzed. The results show that the stress concentration and the stress-intensity factor increase at the crack tip with the advancement of the face; when the stress-intensity factors increase beyond the critical value, the crack expands until the first-weighting. The sufficient condition for modeling the instability was the length s of the branch crack reaching the protection thickness H of the main roof, and the necessary condition was the activation of the crack. The calculation equations of the first-weighting interval and the support resistance were obtained. The influence weights of each parameter on the support resistance are ordered as follows: overburden load q > rock fracture toughness KC > crack length a > main roof thickness h > weighting interval l. Finally, the theoretical analysis results were verified by an in situ monitoring case of the no. 33,206 working face in the Bulianta coal mine, China. On this basis, a reasonable value of the support resistance is further calculated. The results mentioned above can provide a new method for researching the first-weighting of the main roof and can improve the accuracy of the roof control analysis. The research on the mechanisms of first-weighting and the support resistance can effectively promote the safety production of mine, which is in line with the concept of green and sustainable development of the mine.

Study on rib spalling control of shortwall drilling mining technology with a large mining height

The drilling shearer and drilling mining technology has been developed in order to effectively control the rib spalling of a shortwall with a large mining height face in a soft thick coal seam. Working face no. 1305 of the Zhaozhuang Coal Mine was taken as the research subject. The rationality and superiority of shortwall drilling mining technology with a large mining height (SDMTLMH) were explained by combining the theoretical analysis with a numerical simulation. First, based on the occurrence characteristics of the immediate roof, the mechanical model of a simple supported beam was established to calculate the maximum unsupported roof distance. The advance of the working cycle was determined. Then, based on the spatial mobilization plane (SMP) theory, the abutment pressure distribution in the reserved coal was deduced by establishing the unit mechanical model. The appropriate range of the width of the reserved coal (WRC) was determined according to the principle of conservation of energy. Finally, six drilling mining schemes were proposed according to the range of the WRC. In addition, we redeveloped the constitutive model of supports and compacted rock mass in the gob using FLAC3D software. The distribution of the abutment pressure in the drilling mining face and the control effect of the rib spalling were obtained. It was proved that the SDMTLMH can effectively suppress rib spalling and roof fall. The distribution of the strain energy and the external potential energy in reserved coal in six schemes was plotted by Surfer software. The rationality of the theoretical analysis was verified. Considering the caving effect of the reserved coal, the control effect of rib spalling, and the appropriate advancing speed of the working face, the appropriate WRC was determined to be 0.4 m. A field investigation showed that the control effect of rib spalling for working face No. 1305 was much better than that of other large mining height faces in this coal mine.

Research on Technology of Supporting in Super‐Large Section Cut in Working Face with Large Mining Height

For the support problem of the super‐large section cut in working face with large mining height, the 1105 cut pilot chamber of Zhaogu No. 2 Mine, the roof strata structure detection and the strata movement rule research were conducted. The results prove that concentrate fracture area, gradually sparse fracture area, and rare fracture area regularly distributed from the surface to the deep area of the roof of 1105 cut, and less fracture exists in the rock stratum of roof above 3.5 m, and the stratum of roof within the range of 4–6 m is stable. Authors propose the long bolt and cable combined supporting technology and optimized the design plan applying theoretical calculation and computer numerical simulation. The scheme has been applied in the field of the 1105 super‐large section cut in Zhaogu No. 2 Mine. The monitoring results show that the scheme can effectively control surrounding rock of roadway, and the support with long bolt has good effectiveness.

Mechanical characteristics of drum shearer with large mining height under oblique cutting

In order to study the dynamic characteristics of the shearer with large mining height of 8.8 m under Oblique cutting, the spatial mechanical model of the Shearer under oblique cutting was established, the angle between the drum and the working face, the load of the drum and the dynamic characteristics of the fuselage are analyzed by discrete element method and dynamics. The results show that the maximum feed rate of the front drum is 1940mm, the maximum feed rate of the back drum is 1570mm, and the angle between the front drum and the coal wall reaches a maximum of 8° at 64s, and the cutting resistance of the front drum reaches a maximum at 80s, and finally fluctuates up and down at 3.5×105N, the cutting resistance of the back drum increases with the cutting depth, and finally fluctuates up and down at 3.0×105N. The load of the front drum is 1.2 times of that of the back drum. In the process of Oblique cutting, the support force on the lower surface of the front sliding shoe increases by 3.5×105N, the support force on the lower surface of the rear sliding shoe decreases by 2.5×105N, the support force on the upper surface of the front guiding sliding shoe increases by 1.1×105N, and the support force on the upper surface of the rear guiding sliding shoe decreases by 2.3×105N, the whole machine has the tendency of forward turning and side turning to the coal wall. The average radial force between the front rocker arm and the fuselage pin is about 1.8×106N, the average radial force between the front cylinder and the fuselage pin is about 2.2×106N, and the average radial force between the rear rocker arm and the fuselage pin is about 8.0×105N, the average radial force between the rear cylinder and the PIN shaft is about 1.3×106N, which shows that the radial force at the front of the fuselage, the rocker arm and the height of the pin shaft is obviously larger than that at the rear of the fuselage. The research results are important for the design and development of large mining height shearer.

Research on key technologies of intelligent working face in coal

Mining of fully mechanised intelligent working face with large mining height (MFMIWF-LMH) is a technology which allows the mining of 3.5-8.8 m thick coal seams at one time using a whole set of full...

Study on Controlling Technology for Surrounding Rock in Withdrawal Channel of Full-Mechanized Caving Mining with Large Mining Height Face of Super High Seam

In order to solve the problems such as serious damage of the withdrawal channel and wall caving of tunnel side at end mining stage of 21604 fully-mechanized caving mining face of Huangyuchuan coal mine, study the deformation of surrounding rock of the withdrawal channel in 21604 working face and the law of destruction based on a large number of measured field data; the results show that when the working face is 10 m away from the withdrawal channel, the maximum roof subsidence is 300 mm, and the axial force of roof anchor rod reaches 52 kN, exceeding the anchoring force of anchor rod (50 kN); when it is 5 m away from the withdrawal channel, the maximum roof subsidence is 610 mm, and the axial force of side anchor rod reaches the peak value of 48 kN; when the working face passes through the withdrawal channel, the borehole stress meter reaches the peak value of 22 MPa, the withdrawal channel is seriously damaged, and the depth of tunnel side wall caving reaches 700 mm at maximum. According to the deformation characteristics of the surrounding rock of withdrawal channel, it is proposed to adopt the grouting reinforcement for the mining side and the anchor mesh cable combined with reinforced support for the non mining side and roof on the basis of the original support. It has been successfully applied in 21605 working face, and the support effect is remarkable.

Pressure Control Technology at the Hard Thick Sandstone Roof in an Island Mining Face with a Large Mining Height

Pressure Control Technology at the Hard Thick Sandstone Roof in an Island Mining Face with a Large Mining Height

Feasibility study on fully mechanized large mining height long wall top-coal caving mining in ultra-thick (20–30 m), parting-rich coal seams: A case study of the Laosangou mining field in China

ABSTRACT To analyze the feasibility of fully mechanized large mining height long wall top-coal caving mining (LLTCC) in ultra-thick (20–30 m), parting-rich coal seams, a case study on No. 6 coal seam of the Laosangou mining field was conducted. First, the distribution pattern of the coal-seam structure was mastered and generalized based on the coal-seam thickness, parting thickness, and parting horizon. On this basis, physical simulation and UDEC simulation were performed to analyze the top-coal fracture characteristic and the impact of partings. The top-coal caving of No. 6 coal seam was systematically evaluated with statistical results of coal-seam recovery height (h re) and mining–caving ratio (R mc). Finally, the range of mining height (h) at LLTCC faces was determined as an indicator for the division of LLTCC feasible regions in the Laosangou mining field, which is based on the R mc, h re, coal-wall stability, and equipment selection. The results show that the top-coal caving structure of LLTCC faces can be divided into four layers which were effected by top-coal thickness and upper-horizon partings. LLTCC in ultra-thick (20–30 m), parting-rich coal seams was highly feasible. The top-coal cavability of No. 6 coal seam was good overall, and the R mc was about 1:2.89–1:3.91. Direct mining regions (h = 4.0–5.3 m) and buffer mining regions (h = 5.3–6.0 m) of LLTCC were 52.66% and 42.96%, respectively. This study can be used as a reference for the design of LLTCC in similar coal mines.

Research on and Application of Roof Management Technology in 8.8m Ultra-high Fully Mechanized Mining Face

Aiming at the problems of high mining intensity and difficult roof management in a fully mechanized mining face with an ultra-high mining height of 8.8m, this article predicts the pressure parameters and rules of the working face based on the roof management technology of the 12402 fully mechanized mining face in Shangwan Coal Mine. The selection of the working surface bracket and the on-site roof safety management system are explained and analyzed. The results show that the analogy method can be used to predict the mining pressure parameters and rules of the working face to meet the needs of the application of large mining heights; the conventional techniques such as forced caving, “Scraped roof support moving method” and “Advanced drawing support method” are still effective under the condition of 8.8m mining height. The roof safety management system formed during construction guarantees the safe and efficient production of the ultra-high mining height working face, and provides a reference for the popularization of the mining technology of ultra-high mining height.

Movement Law of Overlying Strata with Loading Effect in the Large Space Structure of Deep Mines

Under the action of high-stress field, overlying strata with load characteristics in large space structure formed by changes of working faces in deep mines intensifies the movement of the overlying strata on the working face, which may easily cause dynamic disasters at the working face. Considering the large space structure of deep mines and taking gob-side entry retaining as a breakthrough point, this study analyzes various types of overlying strata structures and their loading effects. The concept and differentiation method of deep “three layers” are introduced. The movement of the overlying strata with loading effect is analyzed by establishing a large-scale Flac3D numerical calculation model and on-site inspection. The results indicate that the “arch” structure formed by the working face shifts to the middle and rear parts of the working face under the influence of the large space structure, and the overlying strata continuously evolves upward during this process. Finally, the “arch” structures of the working face are integrated within the overlying strata to form a symmetrical structure. In the deep “three layers,” “Mk” provides the force source for normal weighing of the working face. “Mj” shifts the stress relief of the working face to the middle–rear position, which may easily cause strong strata pressure at the working face. The uniformly distributed load of “My” ensures the stress relief position at the working face. Through on-site monitoring, the disturbance range and stress of Working Face 418 with large mining height are greater than those of Working Face 416. The changes in pressure relief positions of the working face are as follows: ventilation roadway > middle > intake roadway.

Roof fracture and front abutment stress evolution of large mining height coal face with weak overburden under goaf

The mining pressure evolution of large mining height coal face with weak overburden under goaf is complicated, significantly influencing mining safety. This study uses the actual geological conditions of the II3 coal seam in Lingdong Coal Mine as research background. First, we combine the key layer theory and roof and floor lithology, the middle sandstone strata are determined as key strata. The fracture thin plate model for weak overburden with large mining height is established, considering elastic-plastic theory. We then obtain the calculation formula of key strata initial fracture span lo, periodic fracture span l0, and front abutment stress. Second, the roof fracture and front abutment stress evolution during lower coal mining are obtained using the FLAC3D numerical simulation method. As the coal face advances, the immediate roof continues to collapse, and periodic fracture subsidence occurs. The coal face periodically appears, causing the phenomenon of roof subsidence acceleration, serious coal wall spalling, increasing pillar stress, and roof-stepped subsidence. The numerical simulation results show that the initial fracture span is approximately 25 m, and the stress of the key strata is approximately 12.5 MPa. The roof weighting span of the first cycle is approximately 2.39 m, the front abutment stress peak is approximately 14.33 MPa, and the influence range of the front abutment stress is approximately 17.50 m. Finally, comparing the numerical simulation results with the theoretical results shows that the evolution is similar, verifying the correctness of the mechanical model. The research results can predict the periodic weighting of overburden and provide a reference for the design of roof mining pressure control for large mining height coal face with weak overburden of lower coal seam.

Rib Spalling 3D Model for Soft Coal Seam Faces with Large Mining Height in Protective Seam Mining: Theoretical and Numerical Analyses

Fully-mechanized mining of coal face with a large cutting height is generally jeopardized by rib spalling disaster in the working face. Preventive measures based on undisturbed coal seam conditions fail to provide safe predictions, as large-scale fractures in soft coal face frequently appear before excavation due to mining-induced stresses. This paper investigates a case study of the Paner Mine 11224 working face in the Huainan mine area, China, which features an overlying protected layer in the protective seam mining. To simulate the failure process in such a mine, we elaborated a simplified physical-mechanical model of a coal wall that underwent shear failure and sliding instability, in compliance with the triangular prism unit criterion. Similar simulation experiments, theoretical calculations, and borehole monitoring were used to comprehensively analyze the overburden fracture and movement after mining the lower protective seam. The development height of three overburden zones was determined, and the characteristics of the protected layer affected by mining were obtained. The results show that the failure is mainly related to the roof load, coal cohesion, internal friction angle, coal seam inclination, and sidewall protecting force. The key to limiting the frictional sliding of a slip body is to reduce the roof load and increase the sliding coefficient and cohesion of the main control weak surface (MCWS). Besides, a self-developed three-dimensional numerical calculation software RFPA3D (Realistic Fracture Process 3D Analysis), which considered the rock heterogeneity, was used to reproduce a weak triangular prism’s progressive failure process. The numerical simulation results agreed with the fracture pattern predicted by the theoretical model, which accurately described the rib spalling mechanisms in a soft coal face with a large cutting height and a protective layer.

Analysis on Catastrophe Theory during First Weighting Sliding Instability and Support Crushing of Main Roof with Large Mining Height in Shallow Coal Seam

Roof sliding and instability along the coal wall usually occur in the working face at large mining heights during the process of the first weighting, which causes roof cutting and support crushing. A mechanical model consists of the main roof, immediate roof, and support based on the nonlinear characteristics of the failure and instability of the immediate roof under the abutment pressure, which we constructed to study the step sinking of the main roof, as well as to assign the reasonable value of the support resistance during the first weighting. The instability mechanism of the system was studied by the catastrophe theory and the principle of energy conservation. A conclusion was drawn that the combined cantilever beam structure for the immediate roof will form with the increase of the mining height, and the instability of the immediate roof causes the catastrophic instability of the system. The system instability was found to be related to the stiffness ratio K, material parameters, the load Q, and the first weighting interval of the main roof by analyzing the necessary and sufficient conditions for system instability. The influence degree of each parameter on the stiffness ratio K was as follows: elastic modulus E > support stiffness k1 > cross-section area a > immediate roof thickness H. The calculation equations of support resistance and subsidence of roof step were obtained. The method of judging the roof instability using catastrophe theory was proved as reasonable on the basis of the monitoring example of no. 12401 working face in Shendong mining area, China. On this basis, a reasonable value of support resistance was further calculated, and the working face was maintained safely when the support resistance exceeded 19,232 kN.