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A novel block–particle discrete-element simulation method that matches the double medium of overlying rock (OLR) and loose layer (LSL) in coal mining is developed in this study. This method achieves the collaborative failure characteristics of mining damage under the conduction of double media between the OLR and LSL by combining the self-weight stress loading of the LSL and the breakage morphology of the bedrock top. Based on this, the conduction law of high-strength mining damage in the double medium in a western mining area is simulated and analyzed. The combining effect of the OLR breakage morphology and LSL characteristics on the surface-subsidence characteristics is analyzed and verified based on on-site measurements. The results indicate that the OLR is guided by the "double-control layer and thick-soft rock buffer layer" and shows "grouping subsidence", whereas the surface forms collaborative subsidence with the thick-soft rock buffer layer. In the ultra-full mining stage, the surface presents an "asymmetric inverted trapezoidal" subsidence trough shape. The simulation results agree well the on-site measurements in terms of the surface-subsidence and bedrock-subsidence coefficients. The proposed simulation method provides a scientific approach for investigating the micro-conduction mechanism of mining damage under the effect of high-strength mining in western mining areas. It will benefit future investigations pertaining to the characteristics of OLR breakage and surface subsidence under conditions such as LSL thickness and proportion. [ABSTRACT FROM AUTHOR]

Abstract A novel block–particle discrete-element simulation method that matches the double medium of overlying rock (OLR) and loose layer (LSL) in coal mining is developed in this study. This method achieves the collaborative failure characteristics of mining damage under the conduction of double media between the OLR and LSL by combining the self-weight stress loading of the LSL and the breakage morphology of the bedrock top. Based on this, the conduction law of high-strength mining damage in the double medium in a western mining area is simulated and analyzed. The combining effect of the OLR breakage morphology and LSL characteristics on the surface-subsidence characteristics is analyzed and verified based on on-site measurements. The results indicate that the OLR is guided by the “double-control layer and thick-soft rock buffer layer” and shows “grouping subsidence”, whereas the surface forms collaborative subsidence with the thick-soft rock buffer layer. In the ultra-full mining stage, the surface presents an “asymmetric inverted trapezoidal” subsidence trough shape. The simulation results agree well the on-site measurements in terms of the surface-subsidence and bedrock-subsidence coefficients. The proposed simulation method provides a scientific approach for investigating the micro-conduction mechanism of mining damage under the effect of high-strength mining in western mining areas. It will benefit future investigations pertaining to the characteristics of OLR breakage and surface subsidence under conditions such as LSL thickness and proportion.

Water-rich open-pit mines can have problems with large water inflows, slope reinforcement difficulties, and hazardous mining risks. The construction of a water cut-off curtain to control groundwater in the loose layer of an open-pit mine can effectively reduce the amount of water that must be pumped and eliminate the problem of flooding in the pit. However, the rise of the water level outside the curtain and changes in the geotechnical properties of the slope's material will affect the stability and safety of the pit's slope. A computational model was constructed and limit equilibrium and numerical simulation methods were used to determine the influence of a water cut-off curtain on the stability of the slope. Results show that with the the water cut-off curtain, the water level outside of the cut-off curtain in the loose layer of the open-pit mine continues to rise and the hydrostatic pressure and horizontal thrust of the slope body increases. As a result, the sliding force of the slope increases and the resisting force decreases, ultimately lessening the slope- stability coefficient (factor of safety) of the open pit. If the construction position of the curtain is moved outward, the stability coefficient of the slope will increase, assuming that the water level outside the curtain remains unchanged. Conversely, if the position of the curtain is moved toward the pit, the stability coefficient of the slope will decrease. The maximum shear stress on the slope increases as the water level outside the water curtain rises. The maximum shear stress is mainly concentrated at the toe of the slope of the first bench below the surface and at the interface between the curtain and the bottom of the loose material. If designed properly, the water curtain can control the water table in the slope's material, maintaining the stability of the slope. [ABSTRACT FROM AUTHOR]

Abstract Coal mining under the geological conditions of a loose layer will lead to the intensification of surface movement and deformation, and mining under the geological conditions of a fault will lead to the living slip of a fault. Mining under both conditions will have a great impact on the safety of coal production. To reveal the evolution law of the coupling mechanism of loose layer and fault on the multi-physical fields of overburden, the numerical simulation method is used to simulate the coupling of loose layer and fault with different thicknesses, analyze the changes of vertical stress on the key strata, the changes of surface subsidence, the evolution of elastic energy on the fault zone and the changes of activated slip area of the fault zone. The simulation analysis shows that the vertical stress change trend of the key strata gradually changes from the "V" shape to the "W" shape at the beginning of mining, and the vertical stress concentration will occur at the fault. The loose layer will promote surface subsidence, and the fault will hinder the surface subsidence to a certain extent. The loose layer and the fault alternately affect the surface subsidence. The elastic energy accumulation on the key strata is mainly concentrated on both sides of the goaf. The elastic energy in the center of the goaf is dissipated. The elastic energy accumulation in the fault zone starts from the shallowly buried fault and gradually develops to the deeply buried fault. The instability of fault activation has gone through the initial stage of activation—the intensification stage of activation—the stable stage of activation. Under the working conditions of no loose layer, thin loose layer, and thick loose layer, the fault zone is the first to undergo living slip, and under the action of an extra-thick loose layer, there is a certain lag in the activation slip of the fault zone.

With abundant mineral resources, many types of mining industry and many mines, mining development in China has led to the decline of groundwater level around the mines, waste of water resources, water quality pollution, surface collapse, land degradation, reduction of vegetation cover, and different degrees of impact on groundwater resources and ecological environment. In order to solve the problems of water waste and ecological damage caused by the lateral recharge of water from the strong seepage loose layer to the mine pit, we proposed a vertical curtain water interception technology with flexible magnetic suction membrane to protect the groundwater resources and ecological environment of coal mines. We firstly studied the performance of the suction membrane material, developed the magnetic absorption suction membrane connection process, and carried out indoor tests of different suction membrane connection processes, then we conducted a 1 369 m strong seepage loose layer water interception curtain field test application in the test mine. The research results show that the impermeable membrane has low permeability coefficient, dense structure, high flexibility, resistance to deformation and durability, and is a good material for water cut, pollution control and seepage control, which can meet the requirements of vertical curtain for the strong seepage loose layer of the mine. The self-developed magnetic suction joint material and connection process solved the problems of shallow laying depth, joint leakage and complicated operation of existing connection processes such as overlapping lap, joint lock and joint box, etc. The construction depth of suction membrane curtain connected by magnetic suction joint is not limited by the connection conditions, and the water interception effect of magnetic suction joint connection process is better than that of overlapping lap and joint lock (joint box) connection process. Through the test of making, laying, connecting and backfilling the curtain into a wall with 2 kinds of flexible magnetic absorbent impermeable membranes, the gap at the joint of the impermeable membrane was reduced from 5-20 cm to 0, and the two adjacent impermeable membranes were closely connected as an organic whole, which reduced the water passage of the interception curtain at the joint. Through the mine-field site test, it was found that the water catchment pits below the curtain which had been filled with strong seepage loose layer water leakage for a long time, had dried up, and the water level of strong seepage loose layer outside the curtain had increased by 5.55-9.12 m, and the water level inside the curtain had decreased by 3.21-5.84 m, so the protection of strong seepage loose layer water resources had achieved good results.

The loose layers and shallow weathered bedrock in western China are rich in water, and the inclined shaft crossing the water-rich loose layer is prone to leak at the wellbore construction joints, concrete joints and wall cracks. Leakage will lead to the deterioration of underground working environment, lower working efficiency, increase the burden and cost of underground drainage, and affect the safety of coal mine production. In order to solve the above problems, this paper analyses the characteristics of water seepage in slanting coal mine shafts from the perspective of protecting groundwater resources and safe operation of shafts, and the existing management measures such as drainage, post-wall grouting, rotary pile spraying and curtain grouting. And the principle and structure of soil-cement curtain with equal thickness of water leakage level in inclined shaft, the basis of parameter selection and the method of curtain construction were studied. The effects of formation conditions, comprehensive moisture content, cement content and other factors on the performance of cement curtain were analyzed. The field test application of water leakage control of inclined shaft was carried out in test mining area. The research results shows that the water leakage of inclined shaft in coal mine mostly occurs in the bottom plate, waist wall and the joint of both, and the water inflow was tens of m3/h～ hundreds of m3/h, and some even had water gushing and carrying sand, endangering the safety of the shaft. The equal-thickness soil-cemented curtain forms an equal-thickness wall with uniform thickness, few joints and high water interception rate in the outer stratum of the slanting coal mine shaft through three steps: lateral cutting, retraction cutting and mixing, and slurry mixing to form a wall. It effectively blocks the the hydraulic connection between the inclined shaft, the outside loose layer and the weathered bedrock. The strength of the cement curtain of equal thickness is positively correlated with the cement admixture, and the permeability coefficient is negatively correlated with the cement admixture. The performance of the cement curtain of clay stratum is weaker than that of loess and fine sand stratum. The in-situ core sample of the curtain at the demonstration application site has a compressive strength of 8.62MPa and a permeability coefficient of 2.69×10−8 cm/s. The water influx in the borehole is reduced from 16.8 m3/h to about 1.6 m3/h, which is 90.5% less than before the treatment, and achieved good application results. This method can solve the seepage problem of inlcined shaft in loose layer in western China, ensure the safe operation of the well shaft, and protect the groundwater resources.

Coal mining under the geological conditions of a loose layer will lead to the intensification of surface movement and deformation, and mining under the geological conditions of a fault will lead to the living slip of a fault. Mining under both conditions will have a great impact on the safety of coal production. To reveal the evolution law of the coupling mechanism of loose layer and fault on the multi-physical fields of overburden, the numerical simulation method is used to simulate the coupling of loose layer and fault with different thicknesses, analyze the changes of vertical stress on the key strata, the changes of surface subsidence, the evolution of elastic energy on the fault zone and the changes of activated slip area of the fault zone. The simulation analysis shows that the vertical stress change trend of the key strata gradually changes from the "V" shape to the "W" shape at the beginning of mining, and the vertical stress concentration will occur at the fault. The loose layer will promote surface subsidence, and the fault will hinder the surface subsidence to a certain extent. The loose layer and the fault alternately affect the surface subsidence. The elastic energy accumulation on the key strata is mainly concentrated on both sides of the goaf. The elastic energy in the center of the goaf is dissipated. The elastic energy accumulation in the fault zone starts from the shallowly buried fault and gradually develops to the deeply buried fault. The instability of fault activation has gone through the initial stage of activation—the intensification stage of activation—the stable stage of activation. Under the working conditions of no loose layer, thin loose layer, and thick loose layer, the fault zone is the first to undergo living slip, and under the action of an extra-thick loose layer, there is a certain lag in the activation slip of the fault zone. [ABSTRACT FROM AUTHOR]

The corrosion resistance of zinc–aluminum–magnesium steel plates (Zn–Al–Mg steel plates) is significantly higher than that of galvanized steel plates. However, the unsatisfactory bonding performance of Zn–Al–Mg steel plates significantly limits their widespread application. In this study, X-ray photoelectron spectroscopy is employed to detect changes in the surface oxygen content of Zn–Al–Mg steel plates after different temperature treatments to confirm the existence of surface loose layers. In particular, changes in the surface oxygen content of the Zn–Al–Mg steel plates after the oxide layer is removed are investigated under saturated H2O vapor and O2 environmental conditions, and the cause of the formation of loose surface layers is determined. The uneven distribution of elements on the surface of the Zn–Al–Mg steel plates is investigated with scanning electron microscopy and energy dispersive spectroscopy. Nuclear magnetic resonance is employed to determine the size of the network spatial structure formed by silane coupling agents under different hydrolysis conditions and to further investigate the bonding performance of hydrolysate-modified Zn–Al–Mg steel plates. Several typical automotive adhesives are utilized to compare and examine the changes in the tensile strength of the Zn–Al–Mg steel plate bonding before and after modification with the silane coupling agent and analyze the structural damage of the adhesive at the bonding interface. The results confirm that the silane coupling agent strengthens the loose layer on the surface of the Zn–Al–Mg steel plate. [ABSTRACT FROM AUTHOR]

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Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Loose layers are the locus of human activities. The high-quality 3D modeling of loose layers has essential research significance and applicability in engineering geology, hydraulic and hydroelectric engineering, and urban underground space design. To address the shortcomings of traditional 3D loose-layer modeling based on borehole data, such as the lack of bedrock surface constraints, simple strata pinch-out processing, and the higher fitting error of the strata surface, a 3D loose-layer modeling method based on the stratum development law is proposed. The method mainly uses three different virtual boreholes, bedrock-boundary virtual boreholes, pinch-out virtual boreholes, and densified virtual boreholes, to control the stratigraphic distribution. Case studies demonstrate the effectiveness of this 3D loose-layer modeling method in the Qinhuai District of Nanjing and Hangkonggang District of Zhengzhou. Compared to the previous methods that interpolated stratigraphic surfaces with elevation information, the method proposed in this article interpolates the stratum thickness based on stacking, which could improve the interpolation accuracy. In the area where the loose layers and exposed bedrock are alternately distributed, stratigraphic thickness errors’ mean and standard deviation decreased by 2.11 and 2.13 m. In the pure loose-layer area, they dropped by 0.96 and 0.33 m. In addition, the proposed approach allows us to infer the different stratigraphic distribution patterns accurately and complete 3D loose-layer model construction with higher accuracy and a good visualization effect.

The surface subsidence is the result of the coupling movement of the overlying bedrock and the loose layer. In essence, it is a mechanical problem. Based on the relevant knowledge of soil mechanics and rock mass mechanics, the mechanical model of loose layer slip fracture is established, the expression of loose layer slip angle is deduced quantitatively, and the structural model of loose layer slip and surface and bedrock fracture position is established. The rationality of the mechanical expression and the reliability of the results are analyzed and verified by numerical simulation experiments and field measurements. The results show that (1) the fracture angle of loose layer is 1/2 of the internal friction angle; and (2) there are two types of loose layer sliding structure: "lower large and upper small" type and "lower small and upper large" type. Then, it forms the composite motion structure types of loose layer: "outer arc," "inner arc," "steep-slow-steep," "slow-steep-slow." [ABSTRACT FROM AUTHOR]

The microheterogeneous model makes it possible to describe the main transport properties of ion-exchange membranes using a single set of input parameters. This paper describes an adaptation of the microheterogeneous model for describing the electrical conductivity and diffusion permeability of a track-etched membrane (TEM). Usually, the transport parameters of TEMs are evaluated assuming that ion transfer occurs through the solution filling the membrane pores, which are cylindrical and oriented normally to the membrane surface. The version of the microheterogeneous model developed in this paper takes into account the presence of a loose layer, which forms as an intermediate layer between the pore solution and the membrane bulk material during track etching. It is assumed that this layer can be considered as a “gel phase” in the framework of the microheterogeneous model due to the fixed hydroxyl and carboxyl groups, which imparts ion exchange properties to the loose layer. The qualitative and quantitative agreement between the calculated and experimental concentration dependencies of the conductivity and diffusion permeability is discussed. The role of the model input parameters is described in relation to the structural features of the membrane. In particular, the inclination of the pores relative to the surface and their narrowing in the middle part of the membrane can be important for their properties.

Water and sand inrush is one of the many disasters in mining operations in Western China and is closely linked to the characteristics of loose layers. Therefore, it is very important to study the mechanism of water and sand inrush under different loose layer conditions for recognizing and preventing water and sand inrush. In this article, a mechanical model of water and sand inrush was established, and the limit equilibrium conditions of water and sand inrush under different clay contents in the loose layer were studied. On this basis, physical experiments of water and sand inrush through loose layers with different clay contents were carried out. The results showed that both the 5 and 10% clay contents in the loose layer promoted the occurrence of water and sand inrush. However, compared with that of the 5% clay content, the possibility of water and sand inrush was weakened under the condition of 10% clay content. When the clay content was 20%, the sand body remained stable, inhibiting the occurrence of water and sand inrush. After the test, "collapse pits" were observed on the upper surfaces of the loose layers with 0, 5 and 10% clay contents. However, the upper surface of the loose layer with 20% clay content had only a small depression, and no collapse pit was observed. The results of this study provide experimental guidance for research on water and sand inrush of mining-induced cracks in loose layers with different clay contents. [ABSTRACT FROM AUTHOR]

The loose layer can appear on the rake face of a turning tool under certain cutting conditions and have an important influence on the rake face wear. In this paper, wear morphology and wear mechanism of loose layer on the rake face of the original turning tool and the new cemented carbide micro groove turning tool developed independently during the cutting process are studied, by the combination of theoretical analysis and cutting test. And the relationships between the diffusion wear and the adhesive wear of the loose layer on the rake face of the new micro groove turning tool are further analyzed and revealed. The research results show that the loose layer on the rake face of two turning tools is caused by the diffusion wear, which is formed by the brittleness-weakening of tool material in the region resulting from elements diffusion. Meanwhile, the wear degree of the rake face of tools is aggravated by the mutual promotion of diffusion wear and adhesive wear. In the normal wear stage, the degree of looseness and brittleness of the rake face of the original turning tool is greater than the one of the micro groove turning tool. In the severe wear stage, cobalt elements in the rake face of the two turning tools are dissolved and diffused in varying degrees, which further aggravates the brittle-weakening of materials in the region. But the degree of loose brittleness of the rake face of the original turning tool is still greater than the one of the micro groove turning tool. It can be concluded that the micro groove on the rake face of the new turning tool can improve the rake face wear to a certain extent. [ABSTRACT FROM AUTHOR]

Surface subsidence caused by underground mining is a complicated spatiotemporal process. This study establishes a novel mining subsidence superposition model using variable mining thickness of coal seam by combining two models based on rock rheology theory and the Weibull subsidence method. This model better characterises the surface subsidence mechanism under geological conditions of thick bedrock and thin loose layer, and the prediction results are close to actual measurements. The bedrock and loose layer are considered viscoelastic beam and homogeneous body, respectively. The bedrock and loose layer are analysed using the theories of mechanical movement and mathematical models, respectively. Based on actual geological conditions of a mine in East China, the mechanical parameters were substituted into the Weibull composite subsidence prediction model (WCSPM) and the probability integral composite subsidence prediction model (PICSPM), and the predictions of surface subsidence movement parameters were obtained. The prediction results of the WCSPM are closer to the measured surface subsidence values, thereby verifying the applicability of the theoretical model in engineering practice. This model enables the construction of structures in mining-induced subsidence areas with confidence. • Subsidence deformation of thick bedrock studied using rheology theory. • Weibull distribution equation was used to study deformation of thin loose layer. • The subsidence deformation curves compounded to form novel superposition model. • Model accuracy verified by comparing predicted and actual mining subsidence data. • Dual medium-based WCSPM more suitable for obtaining actual ground subsidence curve. [ABSTRACT FROM AUTHOR]