Search Results (357)

Adjacent, multi-working face mining can expand the range of disturbed overburden, increasing the risk of triggering roof water inrush, which threatens the safe operation of coal mines. In this paper, we propose a risk identification method for roof water inrush under multi-working face mining conditions based on the theory of Key Strata and Full Mining Disturbance. Firstly, the key strata of the overburden are determined based on lithological and structural data from exploration boreholes. A formula is then derived to calculate the critical dimension (L) of the working face that could induce a fracture in the key stratum. The relationship between L and the combined width of the preceding and adjacent working faces is analyzed to assess whether the key stratum is fractured and how it affects the preceding working face. Finally, the height of the water-conducting fracture zone is predicted. The impact of repeated disturbances from multi-working face mining is evaluated to determine whether the height of the water-conducting fracture zone in the preceding working face increases, thereby enabling risk identification for roof water inrush under multi-working face mining conditions. Taking the multi-working faces of the Banji Coal Mine in Anhui Province as a case study, the predicted height of the water-conducting fracture zone is 60 m, with no risk of delayed roof water inrush in the preceding working face. Both numerical simulation results and field measurements of the development height of the water-conducting fracture zone confirm the effectiveness of this method. It is capable of accurately predicting the development height of the water-conducting fracture zone under multi-working face mining conditions and identifying the associated risk of roof water inrush, thus providing a valuable reference for ensuring safe mining operations in multi-working face mining conditions. Full article

Reciprocal structures represent a category of spatial structural systems characterized by mutually supporting connections between components, which are primarily employed in roof systems and spatial frameworks. Insufficient stiffness is a critical challenge for the practical application of reciprocal structures in engineering. This study introduces a new cable-supported reciprocal structure, which integrates rigid beams and flexible cables through struts, inspired by the construction principles of beam string structures. By optimizing the force transfer path, the overall performance of the structure is improved. Through finite element analysis, a comprehensive investigation was conducted on the static behavior and parametric analysis of this new reciprocal structure. The research results show that the rational determination of key parameters, including the rise/span ratio, strut height, and cable length, demonstrates significant efficacy in reducing the maximum displacement of this new reciprocal structure under uniformly distributed load. The stiffness of the new cable-supported reciprocal structure increases by 17% compared to that of the general reciprocal structure, while the total steel consumption decreases by 12%. The proposed new cable-supported reciprocal structure presents an innovative and viable configuration within the domain of reciprocal structures. Full article

Deep coalbed methane (CBM) reservoirs hold substantial resource potential and play a crucial role in China’s unconventional natural gas development. However, the vertical propagation behavior of hydraulic fractures in deep CBM formations remains inadequately understood, posing challenges for optimizing fracturing parameters to control fracture height growth and enhance fracture development within the coal seam. To address this, this study establishes numerical simulation models to investigate hydraulic fracture propagation in directional wells, incorporating three typical lithological combinations representative of deep CBM reservoirs. Through these models, the influence mechanisms of bedding density, stress ratio, rock friction coefficient, and fracturing parameters on vertical fracture propagation and post-fracture productivity were systematically analyzed. The results reveal that the fracture propagation characteristics vary significantly with lithological combinations. Initially, hydraulic fractures penetrated adjacent formations near the wellbore while simultaneously generating branched fractures, leading to the formation of a complex fracture network. As propagation continues, branch fractures exhibited reduced width compared to the primary fracture. Well-developed bedding planes in the roof or floor, combined with lower stress ratios and friction coefficients, effectively constrained vertical fracture growth. Furthermore, optimizing fracturing fluid volume, reducing injection rate, and lowering proppant concentration promoted fracture development within the coal seam, thereby enhancing post-fracture well productivity. These findings provide a theoretical foundation for the optimization of hydraulic fracturing strategies in deep CBM reservoirs, contributing to more effective reservoir stimulation and resource recovery. Full article

Bed-separation water hazards are a common and very harmful mining disaster in the mining areas of western China in recent years, which seriously threatens the safe mining of rich and thick coal seam resources in the West. The Yonglong mining area has become a high-risk area for bed-separation water hazards due to its particularly thick coal seams and strong water-rich overlying strata. In view of this, this paper investigates the development height of a water-flowing fractured zone in the fully mechanized caving mining of an ultra-thick coal seam in the Yonglong mining area, the evolution law of the bed separation of overlying strata, and the process of water inrush from a bed separation. Based on the measured water-flowing fractured zone height data of the Yonglong mining area and several surrounding mines, a water-flowing fractured zone height prediction formula suitable for the geological conditions of the Yonglong mining area was fitted. By using discrete element numerical simulation and laboratory similarity simulation, the evolution law of overlying strata separation under the conditions of fully mechanized caving mining in the study area was analyzed, and the space was summarized into “four zones, three arches, and five zones”. Through the stress-seepage coupling simulation of the water inrush process of the roof separation in the fully mechanized caving mining of an ultra-thick coal seam, the migration, accumulation, and sudden inrush of water in the aquifer in overlying strata under the influence of mining were analyzed, and the variation in the pore water pressure in the process of water inrush during coal seam mining separation was summarized. The pore water pressure in the overlying strata showed a trend of first decreasing, then increasing, and, finally, stabilizing. Combined with the height, water inrush volume, and water-rich zoning characteristics of the water-flowing fractured zone of the 1012007 working face of the Yuanzigou Coal Mine, the danger of water inrush from the overlying strata separation of the working face was evaluated. It is believed that it has the conditions for the formation of water accumulation and separation, and the risk of water inrush is high. Prevention and control measures need to be taken on site to ensure mining safety. The research results have important guiding significance for the assessment and prevention of water inrush hazards in overlying strata during fully mechanized longwall top-coal caving of ultra-thick coal seams with similar geological conditions worldwide. Full article

A combination of theoretical analysis, numerical simulation and physical model experiments is used to explore the mechanism of pressure relief and roof blasting effects along the gob-side roadway. The stress and displacement along the gob-side roadway before and after blasting were investigated using discrete unit code (UDEC) software. The results demonstrated that blasting can effectively decrease the peak stress of the coal seam along the gob-side roadway and transfer it to the depth. The maximum displacement of the roof of the gob-side roadway, the coal pillar and the solid coal was reduced from 9.5, 10.8 and 4 cm to 6.5, 2 and 3 cm, respectively, after roof blasting. The experimental results showed that the movement of the overburden strata showed obvious regional characteristics after blasting which included the height of the caving zone on the broken side being 3.3 times higher than that observed on the unbroken side, while the height of the fractured zone was 0.52 times higher. The field application of roof blasting was controlled by a drilling method, micro-seismic monitoring and stress monitoring. The results showed good application effects. This research provides valuable insights for managing the stability of gob-side entries. Full article

To ensure lateral roadway retention in composite hard rock mining roofs, selecting a proper cutting height is crucial. If the cutting height is too low, the residual hard roof may experience secondary fractures under additional stress, which threatens roadway stability and safe mining production. Conversely, if the cutting height is too high, the overlying rock layers may bear uneven stress, increasing the risk of collapse. To conduct a detailed cutting height analysis for composite hard rock roof retention, the 12 1103 working face at the Qiuji Coal Mine was chosen as the research subject. Using the collapse characteristics of a goaf roof and the theory of composite beams, a lateral mechanical model of a goaf roof was constructed. By integrating the ultimate tensile stress theory and the Maxwell model, the optimal cutting height for a composite hard roof was derived. Using UDEC numerical simulation software, a model for lateral roadway retention was established to compare and analyze the roof collapse effects, vertical displacement, and vertical stress at different cutting heights. The results indicated that a cutting height of 7.8 m (with the bottom of the hole 0.48 m from the four gray layers) achieved the best cutting effect. Field engineering tests further validated the rationality of the calculated results. Using field surveys, the cutting height was adjusted from the original 9.35 m to 7.8 m for the 12 1103 working face. With a working face length of 946 m, this adjustment could save approximately 212,900 yuan in drilling construction costs and improve construction efficiency by 15%. This study provides a theoretical basis and practical reference for selecting cutting heights under similar geological conditions. Full article

Roof cutting by dense drilling is one of the main methods of gob-side entry retaining. Taking the 203 working face of the Ruineng Coal Mine as the engineering background, a mechanical model is established to clarify the roof breaking mechanism. Numerical simulation is conducted to analyze the roof cutting effects of different parameters, and reasonable roof cutting parameters are identified. The results show that: ① The increase in roof cutting height is beneficial to roof cutting, but excessive height will cause stress concentration of the ‘key structure’ on the side of the coal pillar. ② It is difficult to cut off the roof when the roof cutting angle is too small, and the cantilever length of the roof increases when the roof cutting angle is too large. ③ The larger the borehole spacing, the smaller the plastic penetration rate between boreholes. The optimal parameters of roof cutting are determined as follows: roof cutting height 8 m; roof cutting angle 15°; aperture size 48 mm; hole spacing at 200 mm. The deformation of the resulting roadway is controllable, indicating that the key parameter determination method is effective. Full article

Airborne pollen monitoring in the city of Vukovar (Northeastern Croatia) was carried out using a Hirst-type spore trap, which was placed on the roof of a building at a height of 15 m above ground level. Over 5 consecutive years of airborne pollen monitoring, 76 pollen types from 45 plant families were identified. Of these, 29 pollen types belonged to arboreal species and 47 to non-arboreal species. Sixty-two percent of the total pollen was non-arboreal pollen. The main pollen types present in the airborne spectrum were Ambrosia artemisiifolia, Betula, Urtica, and Poaceae. Among the arboreal types, the genus Betula is the only taxon producing a high percentage in the pollen spectrum. Regarding allergenicity, A. artemisifolia, Betula, and Poaceae pose the highest allergy risk, while Urtica has a low risk of pollen allergy. Large differences in annual pollen sum and the seasonal dynamics of these dominant taxa during the study period were verified. The presence of the pollen in the air was influenced by weather conditions, showing in particular a positive correlation with the minimum air temperature for Betula and mean air temperature for Urtica, Poaceae, and A. artemisiifolia. However, the pollen concentration in the air was negatively correlated with precipitation for Betula, Urtica, and Poaceae and with humidity for A. artemisiifolia. Full article

The rapid growth of photovoltaic (PV) installed capacity has driven advancements in photovoltaic technology, such as integrating PV panels into building envelopes. Temperature increases are known to negatively impact PV panel performance. This study investigates and optimizes the design of air-based cooling systems for PV roofs using experimental and numerical analyses, leveraging free natural convection for cooling. Experimental measurements included air inlet/outlet, PV panel, and roof surface temperatures. The primary parameters examined in Computational Fluid Dynamics (CFD) for the numerical study were the heights and widths of the air channels between the panels and the rooftop, with heights ranging from 25 mm to 75 mm and widths varying from 200 mm to 400 mm. There are good agreements between the numerical results and experimental measurements after model validation. The results reveal significant temperature non-uniformity across the surface of the PV panels, with a maximum temperature difference of 16.50 °C. The shading effect of the PV panels resulted in an average reduction in roof surface temperature by 12.90 °C. Parametric studies showed that changes in height had a more pronounced effect on cooling than in width. The optimal design was identified with a channel size of 75 mm × 400 mm, resulting in the lowest average PV panel temperature of 65.21 °C and enhanced temperature uniformity, with maximum efficiency reaching 11.54%. Full article

This study investigates how mine backfill interacts with pillars to enhance load-bearing mechanisms in underground mining using the bonded-block modeling method. Through systematic numerical simulations of single- and three-pillar systems, we evaluate critical design parameters—backfill ratio, backfill’s cohesion, lateral confinement pressure, and pillar height-to-width ratio—to quantify their effects on cooperative load-bearing behavior. Key findings reveal that backfill provides essential horizontal passive support to pillars, with this stabilizing effect amplifying as the pillars fragment or undergo lateral expansion. Increasing the backfill-to-roof contact ratio due to the lateral expansion and squeezing effect of the pillar to the adjacent backfill strengthens the lateral constraints, reducing the tensile failures and axial crack propagation in the pillars at peak stress. In multi-pillar configurations, higher backfill cohesion improves system stability by redistributing loads across adjacent structures. Practical guidelines are proposed. Low-cohesion backfill with high filling ratios is recommended for single pillars to absorb energy during sudden failures, while high-cohesion backfill optimizes stability in multi-pillar systems. These insights advance the design of safer and more efficient backfill–pillar support systems in mining engineering. Full article

Studying temperature evolution and distribution range during underground coal gasification is essential to optimize process efficiency, ensure safe and stable operation and reduce environmental impact. In this paper, based on the Liyan Coal Mine underground gasification project, the moving grid setting is used to simulate the moving heat transfer process of the underground coal gasification (UCG) flame working face (FWF). The results showed that the temperature distribution within the coal wall facing the flame is relatively narrow and remains concentrated within a limited range. Temperature distribution curves for T = 100 °C and T = 600 °C initially exhibit a nonlinear increase, reaching a maximum value, followed by a nonlinear decrease, ultimately trending towards a constant value. The maximum temperature influence ranges at ∆T = 10 °C (T = 30 °C) in the roof, left coal pillar, and floor are approximately 13.0 m, 9.0 m, and 10.1 m, respectively. The temperature values at the +1 m and +2 m positions on the roof exhibit a parabolic pattern, with the height and width of the temperature curve gradually increasing. By the end of the operation at t = 190 d, the length range of temperatures exceeding 600 °C at the +1 m position is 73 m, with a maximum temperature of approximately 825 °C, while at the +2 m position it is 31 m, with a maximum temperature of approximately 686 °C. Full article

The architecture of the Orang Asli (OA) in Peninsular Malaysia has always been disregarded in studies of the indigenous people. This study is a venture towards recognizing and classifying the OA dwellings into typologies by outlining the salient characteristics of the physical form for further studies about the OA traditional dwellings. Data are collected through field measurements, interviews, and visual recordings of the identified case studies. Typologies of the OA are formed by analyzing the basic shapes and architectural characteristics, salient architectural features, and materials. This study found that the OA dwellings have sustainable and unique attributes to the sub-ethnicities. The typology classification is the plan and roof form (roof slope degrees), height of the floor from the ground level, opening and geometry, and material used for construction. Full article

This paper proposes a steady-state thermal model for the passive cooling of photovoltaic (PV) modules integrated into a vertical building façade by means of a solar chimney, including an empirical correlation for turbulent free convection from a vertical isothermal plate. The proposed analytical model estimates the air velocities at the inlet and at the outlet of the ventilation channel of such a cooling system and the average temperature of the façade-integrated PV modules. A configuration composed of a maximum of six vertically installed PV modules and one solar chimney is considered. The air velocities at the inlet and at the outlet of the ventilation channel obtained for the case of installing PV modules on the building façade are compared with those calculated for the case where the PV modules are integrated into the roof with a slope of 37°. By comparing each of the solutions with one PV module to the corresponding one with six PV modules, it was found that the increase in the air velocity due to the effects of the solar irradiance and the height difference between the two openings of the ventilation channel ranges between 41.05% in the case of “Roof” and 141.14% in the case of “Façade”. In addition, it was obtained that an increase in the solar chimney height of 1 m leads to a decrease in the average PV section temperature by 1.95–7.21% and 0.65–2.92% in the cases of “Roof” and “Façade”, respectively. Finally, the obtained results confirmed that the use of solar chimneys for passive cooling of façade-integrated PV modules is technically justified. Full article

Hydraulic fracturing can significantly enhance coalbed methane production, with in-situ stress playing a crucial role in this process. Our study focuses on calculating in-situ stress in the deep 8+9# coal seam in the north-central Zijinshan block. Leveraging data from acoustic logging and hydraulic fracturing tests, we developed a stress prediction model tailored to the area’s geology. We analyzed stress’s impact on fracturing behavior and the origins of mechanical anisotropy in deep coal reservoirs using μ-CT imaging. Our results show that the Anderson-modified model, accounting for transverse isotropy, offers greater accuracy and applicability than traditional models. The study area exhibits a normal faulting stress regime with significant stress contrasts and maximum horizontal principal stress aligned with the east-west geological stress direction. After hydraulic fracturing, fractures form a complex fracture system resembling elongated ellipses in the coal reservoir, primarily extending in the vertical direction. To control fracture height and prevent penetration through the roof and floor, regulatory measures are essential. μ-CT analysis revealed the distribution of primary fractures, pores, and minerals in the coal, contributing to mechanical anisotropy. This research advances CBM development in the Zijinshan block and similar regions by refining stress prediction and fracturing propagation methods. Full article

Currently, research on the stability of roadway-side supports in gob-side entry techniques primarily focuses on vertical stress, neglecting the lateral effects induced via roof collapse and waste rock compaction in the mined-out area. This paper systematically investigates the effect of roof rotation and the compression of waste gangue on the lateral load-bearing behavior of the roadway-side support system, combining theoretical analysis with FLAC3D numerical simulations. The results indicate that the lateral load-bearing capacity of the support system is positively correlated with both mining height and the width of the roadway-side support. When the mining height or the support width is small, the lateral load-bearing capacity of the support system is weaker, making it more prone to sliding failure. Furthermore, lateral load control technology for the roadway-side support system is proposed, which includes “roof cutting + increasing width”. When the stress transfer path of the roof is blocked, as the support system width increases from 1 m to 2 m, the lateral load-bearing capacity of the roadway-side support significantly increases and then stabilizes. This results in different extents of expansion in the elastic region within the support system, providing valuable insights for the design of roadway-side supports. Full article