Large Dip Angle Research Articles

Causes and Countermeasures of Collapse in Fully Mechanized Mining Face with Large Dip Angle in Yiluo Coal Industry

Causes and Countermeasures of Collapse in Fully Mechanized Mining Face with Large Dip Angle in Yiluo Coal Industry

Research on the Movement Law of Roof Structure in Large-Inclined Coal Seam Working Face: A Case Study in Liu.Pan.Shui. Mining Area

In the Liu.Pan.Shui. coal field, Guizhou Province, China, 35°∼60° steeply inclined coal seams are widely distributed, and the coal resources present are of high quality and are mostly coking coal. However, because the roof overlying rock structure is affected by the geological conditions at a large dip angle, the combined cantilever beam structure of the overlying rock near the working face and the overlying rock masonry beam structure in front of the working face have different migration laws from when the condition of the near-level coal seam is generated. The pressure has emerged with new characteristics, posing a threat to coal mine production safety. Therefore, by establishing a mechanical model of roof overlying rock structure in accordance with the characteristics of coal seam inclination, mining height, and goaf overlap in the Liu.Pan.Shui mining area and using the analytical formula of material mechanics to calculate the behavior of rock pressure, guide the roof weakening means, construction technology, and parameters. It is used to quantitatively control the transportation load of the overlying rock on the roof of the large inclination coal seam and realize the safe and efficient mining of the precious coal resources of the Liu.Pan.Shui coal field.

Multiview Image Matching of Optical Satellite and UAV Based on a Joint Description Neural Network

Matching aerial and satellite optical images with large dip angles is a core technology and is essential for target positioning and dynamic monitoring in sensitive areas. However, due to the long distances and large dip angle observations of the aerial platform, there are significant perspective, radiation, and scale differences between heterologous space-sky images, which seriously affect the accuracy and robustness of feature matching. In this paper, a multiview satellite and unmanned aerial vehicle (UAV) image matching method based on deep learning is proposed to solve this problem. The main innovation of this approach is to propose a joint descriptor consisting of soft descriptions and hard descriptions. Hard descriptions are used as the main description to ensure matching accuracy. Soft descriptions are used not only as auxiliary descriptions but also for the process of network training. Experiments on several problems show that the proposed method ensures matching efficiency and achieves better matching accuracy for multiview satellite and UAV images than other traditional methods. In addition, the matching accuracy of our method in optical satellite and UAV images is within 3 pixels, and can nearly reach 2 pixels, which meets the requirements of relevant UAV missions.

Analysis and Engineering Practice of Factors Affecting Top‐Coal Recovery in a Large Dip Coal Seam

The recovery of top coal in the caving face directly impacts the efficiency of mining coal resources. The geological conditions and mining parameters are well known to be significant influences on the recovery of top coal. This study focused on the 9‐301 working face, which is located in a thick coal seam with a large dip angle. The influences of the coal seam’s dip angle, mining direction, and coal caving mode and interval on the recovery were analyzed using PFC2D simulation. Field trials were also carried out. The results of the numerical calculations show that the recovery of top coal is clearly affected by the dip angle, with recovery decreasing as the dip angle is increased. Mining from the top to bottom along the dip of the coal seam is beneficial to improve recovery. The top‐coal recovery using the multicycle‐sequence coal caving method is higher than when using single‐sequence coal caving and single‐interval coal caving modes. The top‐coal recovery using “one cutting and one caving” (coal caving interval of 0.8 m) was higher than that under two cuttings and one caving (coal caving interval of 1.6 m). During the field trials, the recovery of top coal under different caving intervals and modes was measured. The results show that the recovery of top coal is optimal when using one cutting and one caving with multicycle‐sequence coal caving modes. The field measurements are consistent with the simulation results. The results of this study can help guide additional research for optimizing the recovery of top coal from thick coal seams with large dip angles.

A free boratriptycene-type Lewis superacid.

Bicyclic pyrazabole-bridged ferrocenes with BH groups at their bridgehead positions were prepared from [Li(thf)]2[1,1′-fc(BH3)2] and pyrazole or 3,5-dimethylpyrazole in the presence of Me3SiCl (1 or 1Me, respectively; 1,1′-fc = 1,1′-ferrocenylene); Me3SiH and H2 are released as byproducts. Treatment of 1 or 1Me with 1 eq. of the hydride scavenger [Ph3C][B(C6F5)4] afforded the borenium salts [2][B(C6F5)4] (72%) and [2Me][B(C6F5)4] (77%). According to X-ray crystallography, [2Me]+ contains one trigonal-planar borenium cation, the cyclopentadienyl (Cp) rings of the 1,1′-fc fragment remain parallel to each other, but the Cp–B bond vector is bent out of the Cp plane by an unprecedentedly large dip angle α* of 40.6°. The Fe⋯B(sp2) distance is very short (2.365(4) Å) and the 11B NMR signal of the cationic B(sp2) center is remarkably upfield shifted (23.4 ppm), suggesting a direct Fe(3d) → B(2p) donor–acceptor interaction. Although this interpretation is confirmed by quantum-chemical calculations, the coupling between the associated orbitals corresponds to an energy of only 12 kJ mol−1. Accordingly, both the experimental (e.g., Gutmann–Beckett acceptor number AN = 111) and theoretical assessment (e.g., Et3PO and F−-ion affinities) of the Lewis acidity proves that [2]+ is among the strongest boron-based Lewis acids available to date.

Research on Flood Discharge and Energy Dissipation of a Tunnel Group Layout for a Super-High Rockfill Dam in a High-Altitude Region

Under the condition of a large dip angle between the flood discharging structure axis and the downstream cushion pool centerline, the downstream flow connection for the discharging tunnel group is poor, and the lower air pressure in high-altitude areas increases its influence on the trajectory distance of the nappe, further increasing the difficulty of predicting the flood discharge and energy dissipation layout. Based on the RM hydropower project with the world’s highest earth-rockfill dam, this paper studies the problem of a large included angle flip energy dissipation layout of a tunnel group flood discharge using the method of the overall hydraulic physical model test. The test results show that the conventional flip outlet mode has a long nappe falling point, a serious shortage of effective energy dissipation space, a large dynamic hydraulic pressure impact peak value on the bottom slab and side wall of the plunge pool, a poor flow connection between the outlet of the plunge pool and the downstream river channel, and a low energy dissipation rate. Considering the influence of a low-pressure environment, when the “transverse diffusion and downward incidence” outflow is adopted, the nappe falling point shrinks by 11 m, the energy dissipation form of the plunge pool is greatly improved, the effective energy dissipation space is increased by 159%, the RMS of the maximum fluctuating pressure is reduced by 74%, the outflow is smoothly connected with the downstream river, the energy dissipation rate is increased by 0.8%, and the protection range of flood discharge atomization is significantly reduced. This effectively solves the safety problems of large included angle discharge return channels and the energy dissipation and erosion prevention of super-high rockfill dams.

Experimental Study on Sweep Characteristics of Gas Gravity Drainage in the Interlayer Oil Reservoir

Stable gas gravity drainage is considered an effective method to enhance oil recovery, especially suitable for deep buried, large dip angle, and thick oil reservoirs. The influence of reservoir heterogeneity on controlling the gas–oil interface and sweep characteristics of injected gas is particularly important to design reservoir development schemes. In this study, according to the interlayer characteristics of Donghe carboniferous oil reservoirs in the Tarim Basin, NW China, 2D visual physical models are established, in which the matrix permeability is 68.1 mD and average pore throat radius is 60 nm. Then, hydrocarbon gas gravity drainage simulation experiments are carried out systematically, and a high-speed camera is used to record the process of gas–oil flow and interface movement. In this experiment, the miscible zone of crude oil and hydrocarbon gas is observed for the first time. The interlayer has an obvious shielding influence, which can destroy the stability of the gas–oil interface and miscible zone, change the movement direction of the gas–oil interface, and reduce the final oil recovery after gravity drainage. The remaining oil mainly is distributed near the interlayers. The higher displacement pressure leads to increased stability of the gas–oil displacement front and later gas breakthrough, which leads to higher oil recovery. The lower gas injection rate contributes to a slower front velocity and wider miscible zone, which could delay gas breakthrough. For the immiscible gas gravity drainage, there is a critical gas injection rate, with which the oil recovery factor is the highest.

An Improved Form of 2D SPH Method for Modeling the Excavation Damage of Tunnels Containing Random Fissures

The excavation damage of deep tunnels is one of the most important factors contributing to the failure of tunnel structures. In order to investigate the influence of tunnel shapes and fissure geometries, the kernel function in the traditional SPH method has been improved, which can realize the brittle fracture characteristics of particles and can be called the Improved Kernel of Smoothed Particle Hydrodynamics (IKSPH-2D). Meanwhile, the random fissure generation method in IKSPH has been put forward. Different tunnel shapes, fissure geometries, and locations are considered during the simulation of tunnel excavation, and results show that (1) the typical “V”-shaped shear damage zones appear after the tunnel excavation, which is consistent with engineering practice. Meanwhile, tunnel excavation also has an “activating” effect on the preexisting fissures. (2) The stability of circular-shaped tunnel is the best, while horseshoe shaped tunnel is worse, and the “U”-shaped tunnel is the worst. (3) Fissures with small and large dip angles have the greatest influence on the stability of tunnel excavation. With the increase of fissure numbers and lengths, the tunnel tends to be instable. (4) The IKSPH method gets free from traditional grids in FEM, which can dynamically reflect the fracture processes of tunnel excavation. Meanwhile, developing 3D IKSPH parallel program will be the future directions.

Experimental investigation on the strain energy evolution mechanism of granite specimens with a single flaw

Damage and fracture of rocks is a comprehensive result of strain energy dissipation and release. In order to study the energy evolution mechanism of hard brittle rock masses during failure process, uniaxial compression tests on the granite specimens with a single pre-existing flaw are carried out with digital image correlation method (DIC). The results indicate that: (1) The stress fluctuation before structural failure corresponds to the sudden increase of the dissipated energy, the essence is that rock masses occur obviously damage and cracking. (2) For medium flaw dip angles, the stress fluctuation occurs repeatedly in stages, whose strain energy is dissipated gradually; for large or small dip angles, the stress fluctuation is almost not appeared, and the energy dissipation is insignificant. (3) With the increase of flaw dip angles, the dissipated energy ratio at the peak stress first increases and then decreases showing an inverted U-shaped, resulting in a similar law of rock damage but a contrary law of strength; the corresponding elastic energy ratio is U-shaped of decreasing first and then increasing, causing the structural failure changes from dynamic to static and then to dynamic again. The results can provide theoretical references for the formation mechanism and prevention method of dynamic disasters of rock underground engineering.

Analysis of Tunnel Lining Failure Mechanism under the Action of Active Fault

The underground structure that crosses the active fault will cause more serious damage under the dislocation of the active fault. Relying on an actual tunnel in the southwest mountainous area to establish a three-dimensional finite element model, the failure mechanism of the tunnel under strike-slip and thrust fault dislocation is revealed from the lining deformation, stress distribution, and plastic zone distribution, and the results show that the damage range of the lining distributes in the area of the fracture and the damage effect is greatly affected by the movement amount of the active fault. The lining damage under the active fault dislocation is mainly tensile damage, while the lining under the thrust fault dislocation shows compression damage on both sides of the fracture when there is a fracture with a large dip angle. The development range of plastic zone is positively correlated with the dip angle of the fracture and the amount of movement, and the development range is negatively correlated with the dip angle of the fracture and positively correlated with the amount of dislocation. The plastic zone range can be predicted, and the key monitoring range can be set according to the movement form of the active fault, the dip angle of the fracture zone, and the amount of fault movement.

Method and Mechanism of Dump Overlying the Bedrock with Large Dip Angle in Opencast Mine

Dump in the steep area of the open-pit mine is essential for safe production. The bedrock with the bumpy-surface blasting method effectively improves the stabilization of the dumpsite. The effect of the ratio and dispersion degree on the deformation and failure of the dumping bench at the largely inclined area was analyzed. Based on the limit equilibrium method, the equation about the stability factor and the blasted region ratio was deduced. Virtual experiments were performed to address how the ratio and dispersion degree affect deformation and failure. The results showed that the stability factor is a quadratic function of the ratio of the blasted area. The increase in the ratio results in a drastic reduction of displacement, and the direction of displacement significantly changes. The rise in the dispersion degree effectively reduces the displacement and shear strain increment, and the failure mode changes. There is a specific value for the ratio and dispersion degree, making the displacement and shear strain increment little. The research on bumpy surface blasting in this paper provides the theoretical foundation for the dump construction at the site with the large dip angle.

Analysis on the Regular of Underground Pressure in Large Dip Angle Coal Seam with Soft Roof and Floor

The dip angle of coal seam in Guanyinshan coal mine is between 32° and 39° and the first mining area is X11 and X12. According to the caving degree of the immediate roof in the gob, the intensity of pressure of the main roof is analyzed, and the dynamic load coefficient of the main roof is small. The three-dimensional simulation software FLAC is used to calculate the distance of initial caving and distance of initial pressure of working face. The initial caving distance of the immediate roof at each part of the working face is about 4 m, and the initial pressure distance of main roof is about 20 m on average. This paper analyzes the caving of the main roof: when the distance of initial pressure is 20 m, the caving height of the main roof is about 4 m; when it is pushed to 30 m, the caving height of the main roof is about 10 m; with the continuous mining of the working face, the caving height of the main roof is also increasing, when it is pushed to 90 m, the caving height of the main roof reaches 18 m. Through the analysis of the regular of underground pressure in large dip angle soft roof and floor coal seam mining, it can guide the production.

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.

The influence of the drilling rate of the raise boring machine on the stability of the surrounding rock of a inclined shaft with large dip angle

The drilling method of counter-well drilling rig has become an important construction method for the construction of large inclination Angle pressure pipeline in pumped storage power station. In order to study the effect of the drilling rate on the stability of the surrounding rock of the inclined well. The method of numerical analysis is used to simulate the drilling rate of backwell drilling machine by changing the drilling depth of certain calculation step, and the drilling depth is along the inclined shaft line. The selection of drilling parameters is optimized and the drilling rate of the reverse well rig is determined. The results show that the tunneling rate has a significant influence on the deformation rate of surrounding rock and the change rate of stress gradient in the process of drilling with reverse-well drill. With the increase of drilling rate, the deformation rate and the change rate of stress gradient increase. The variation amplitude of the surrounding rock deformation and stress value at the monitoring point increases first and then decreases, and finally tends to be stable. Under this formation condition and drilling scheme, the deformation of surrounding rocks in wellbore after drilling at the same depth is small, and the effect of stress disturbance is not significant. The maximum deformation of surrounding rocks in inclined Wells is only 0.27mm, and the strong disturbance zone is about 2.0m. Combined with field drilling test results, the optimal drilling rate of reverse well reaming is determined to be 1.2m/h.

Fracture criterion of basic roof deformation in fully mechanized mining with large dip angle

To explore the structure evolution of overlying strata and pressure characteristics of coal mining with large dip angle, the basic roof mechanical model was established that based on the thin plate theory and the development characteristics of 1212 (3) working face of Panbei Mine. The formula was deduced that used for calculating the basic roof stress distribution in large dip angle coal seam. It revealed the mechanism evolution of mining stress and its influence on overburden deformation. Furthermore, it was also discussed that the effect of false roof on the failure of the basic roof. It showed that the false roof increases the differentiation of gangue’s filling rate in goaf and improves the evolution rate of basic roof fracture. It is the main influencing factor that the large dip angle leads to the “scoop” distribution of the stress and deformation in basic roof. It dominates the evolution of overburden fractures and the regional instability. The maximum deformation of the basic roof is located in the middle and upper part of the working face. This theoretical model is verified by means of numerical simulation and field monitoring.

Effects of dynamic strain rate on the energy dissipation and fragment characteristics of cross-fissured rocks

Internal initiation and propagation of micro cracks in rock materials might result in macroscopic fragmentation and energy dissipation under dynamic strain rate. Understanding the internal mechanism of rock failure and energy consumption is significant in assessing the stability of engineering rock mass under dynamic disturbance. This study experimentally investigated the energy dissipation and fragment distribution of rock specimens containing symmetrical and asymmetrical cross fissures under static and dynamic loadings. Our results reveal that the dynamic strength of rock specimens evidently increases with increasing strain rate, while the dynamic elastic modulus does not depend on the loading rate. For a given dynamic strain rate, the rock specimens containing asymmetrical cross fissures (one of the fissures had a relatively large dip angle) had higher dynamic strengths than those containing symmetrical cross fissures. During loading process, tensile cracks and shear cracks significantly affect the failure patterns of cross-fissured rock specimens under static and dynamic loadings, respectively. All the cross-fissured specimens show similar “X” shaped shear failure mode regardless of fissure configuration subjected to dynamic strain rate. The cross-fissured rock specimens with higher strain rates feature smaller location parameter and scale parameter of the fragment size distribution by GEV fitting. The fractal dimension of cross-fissured specimens show an evident loading rate dependence, and the size distribution of the fragments in asymmetrically cross-fissured specimens under dynamic loading is most homogeneous. The dissipated energy density of all the rock specimens obviously increase as the dynamic strain rate increases, while the energy utilization efficiency is less affected by the strain rate.

Investigation on Surrounding Rock Stability Control Technology of High Stress Roadway in Steeply Dipping Coal Seam

There are a large amount of steeply dipping coal seams deposited in China, the safe and effective extraction of which are the challenge for coal operators due to the complicated geological characteristics, in particular, when the underground roadway is excavated in the steeply dipping coal seams with limited seam distance. The Universal Distinct Element Code (UDEC) was adopted in the present research to explore the stress distribution of surrounding rock of the roadway. Based on the numerical simulation, the damage coefficient was proposed and then used to classify the roof conditions into four groups. After that, the asymmetric support technique was proposed and put into practical applications. It is indicated that the stress concentration on the floor is the main feature of the extraction of steeply dipping coal seams. Moreover, the distributions of the maximum vertical stress and horizontal stress which are much different from each other mainly attributed to the effect of the large dip angle. This research also verified the feasibility of using the asymmetric and partition support technique to maintain the integrity of the surrounding rock, as from the case study conducted at the 12032 longwall coal face of Zhongwei coal mine.

Enhancing the resolution of time–frequency spectrum using directional multichannel matching pursuit

Matching pursuit is able to decompose signals adaptively into a series of wavelets and has been widely applied in signal processing of the geophysical fields. Single-channel matching pursuit could not take into account the lateral continuity of seismic traces, and the recent multichannel matching pursuit exploits the lateral coherence as a constraint, which helps to improve the stability of decomposition results. However, atoms searched by multichannel matching pursuit currently are just shared by lateral seismic traces at the same time slicers. The lack of directionality in multichannel search strategies leads to irrationality in dealing with large dip angle seismic traces. Considering that the waveforms of reflection events are relatively continuous and similar, an improved multichannel matching pursuit is proposed to realize the directional decomposition of adjacent signals. Based on the principle of seismic reflection events tracking and identification, directional multichannel decomposition of seismic traces is realized. The seismic channel to be decomposed is correlated with the time shift of the optimal atom determined by the previous seismic channel. The time position of the maximum correlation indicates the center time of the optimal atom. Optimal atoms identified by one iteration of multichannel decomposition have the same frequency and phase parameters, different center time and amplitude parameters. The center time of the optimal atoms is consistent with seismic reflection events. Tests illustrate that the algorithm can successfully reconstruct 2D seismic data without reducing accuracy. Besides, the application of field data is of great significance for reservoir exploration and hydrocarbon interpretation.

Siliciclastic depositional model within a subsurface coastal parasequence based on barriers and baffles – An application to the Donghe Sandstone Member in the Hudson Oilfield, Tarim Basin, NW China

Detailed analyses of a siliciclastic coastal reservoir highlights the need for an enhanced knowledge of their depositional model. At the scale of the bed sets, however, it is difficult to determine the depositional model, largely due to a limit in vertical resolution of seismic data and conventional wireline logs. Barriers and baffles, following either surfaces of bed sets or beds, act as isochronous boundaries, therefore, holding a key to reveal the sedimentary evolution of subsurface reservoirs at small scales. Calcareous and argillaceous barriers and baffles of the Donghe Sandstone Member in the Hudson Oilfield have obvious low conductivity responses in dipmeter data, therefore, they are interpreted and correlated by integration of conventional logs and dipmeter data. Barriers separate the Donghe Sandstone Member into three retrogradational bed sets (i.e., B1~B3) and two progradational bed sets (i.e., B4~B5), of which beds are constrained by baffles with larger dip angles than barriers in the current structure pattern as well as the period of deposition. The stacking patterns indicate relative sea-level rise within B1~B3 and fall within B4~B5. The relative sea-level changes control the baffle frequency, thickness and length of barriers and baffles. Vertically, the variation of frequency and maximum thickness of both argillaceous and calcareous baffles increase during the transgression yet reduce during regression. Horizontally, the length of barriers and baffles positively correlates with their maximum thickness along the paleoshoreline, as it does the direction perpendicular to the paleoshoreline. Therefore, a depositional model of early retrogradation followed by progradation is built for the Donghe Sandstone Member, a siliciclastic coastal parasequence with upper-shoreface and lower-shoreface facies, based on barriers and baffles. This depositional model is embodied with certain principles of reservoir architecture and behavior.

Natural Fractures in Carbonate Basement Reservoirs of the Jizhong Sub-Basin, Bohai Bay Basin, China: Key Aspects Favoring Oil Production

Analysis of natural fractures is essential for understanding the heterogeneity of basement reservoirs with carbonate rocks since natural fractures significantly control key attributes such as porosity and permeability. Based on the observations and analyses of outcrops, cores, borehole image logs, and thin sections from the Mesoproterozoic to Lower Paleozoic in the Jizhong Sub-Basin, natural fractures are found to be abundant in genetic types (tectonic, pressure-solution, and dissolution) in these reservoirs. Tectonic fractures are dominant in such reservoirs, and lithology, mechanical stratigraphy, and faults are major influencing factors for the development of fractures. Dolostones with higher dolomite content are more likely to have tectonic fractures than limestones with higher calcite content. Most tectonic fractures are developed inside mechanical units and terminate at the unit interface at nearly perpendicular or high angles. Also, where a thinner mechanical unit is observed, tectonic fractures are more frequent with a small height. Furthermore, the dominant direction of tectonic fractures is sub-parallel to the fault direction or oblique at a small angle. In addition, integrating diverse characteristics of opening-mode fractures and well-testing data with oil production shows that, in perforated intervals where dolostone and limestone are interstratified or dolostone is the main lithologic composition, fractures are developed well, and the oil production is higher. Moreover, fractures with a larger dip angle have bigger apertures and contribute more to oil production. Collectively, this investigation provides a future reference for understanding the importance of natural fractures and their impact on oil production in the carbonate basement reservoirs.