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A model of an inclined coal seam floor with linearly increasing water pressure was developed based on theories of ground pressure and key strata. The stability metrics of the water-resistant key strata in the inclined coal seam was deduced using Mohr–Coulomb yield criterion. Five principle factors were selected: the distance that the workface had advanced, the tilted length of workface, the thickness and pitch of the water- resistant key strata, and the elasticity modulus. A sensitivity analysis was then conducted using an orthogonal design. The thickness of the water-resistant key strata was the most important factor, with a 44.8% ranking, followed by the distance that the workface had advanced at 34.4%. The influence of the elasticity modulus, pitch, and tilted length of the workface, were 9.3, 5.8, and 5.7%, respectively. The maximum water pressure possibly tolerated by the inclined aquiclude were found to rise with the increasing load of the caved overburden, and decrease with the increasing workface initial or periodic weighting distance, workface length, and pitch of the water-resistant key strata. A parabolic relationship exists between the maximum allowable water pressure and thickness of the key aquiclude. Water-resistant key strata located in the lower part of the confining layer offers better protection from floor water inrush. These findings provide an important theoretical basis to determine the potential of water inrush from an inclined coal seam when mining above confined aquifers.

The entire overburden stratum above a coal mining area is considered to be composed of an alluvial soil layer and a bedrock layer. In underground mining, alluvial soil has a major effect on ground subsidence. This effect is especially significant and not negligible when the alluvial soil accounts for a large proportion in the entire overlying stratum of coal mining areas covered with thick alluvial soil (CMATASs). In this study, the applicability of the most popular probability integral method (PIM) used for CMATASs was analyzed, and it was found that the PIM is not suitable for ground subsidence prediction in CMATASs for two main reasons: (1) the subsidence basin range predicted by the PIM was smaller than the measured range; thus, the predicted basin converged more rapidly than the measured basin at the edges. (2) Poor fitting results were obtained at the subsidence basin edge. The mechanism of mining subsidence in CMATASs and the reasons why the PIM is not suitable for CMATASs were investigated in terms of the internal deformation and crack (void) distribution within the rock mass induced by underground coal mining. The results indicate that the alluvial soil is compacted and then subsides under vertical compression deformation, which increases ground subsidence. The bedrock is subjected to the weight/load of the thick alluvial soil layer. Because of the vertical compression deformation inside the rock, its internal voids (spaces) are compacted; thus, the replaced voids (spaces) are transferred to the ground surface, resulting in an increase in ground subsidence. However, the effect of the alluvial soil on ground subsidence cannot be detected by the PIM; moreover, the PIM is unable to represent the mechanism of the mining subsidence in CMATASs. Thus, the PIM cannot be used for predicting subsidence in CMATASs. To precisely calculate subsidence in CMATASs, we propose a combined prediction model (CPM) for mining subsidence in CMATASs based on soil mechanics and stochastic medium theory. The new CPM was applied to the mining process in the Huainan Coal Mining Area. The calculation results show that subsidence predicted by the CPM better fits the measured subsidence values, with a relative error of 4.9%, and that the fitting accuracy is improved by 18% compared to the relative error of the PIM (6.0%). Thus, the proposed CPM is more suitable for predicting ground subsidence caused by underground coal mining in CMATASs, and can be used to provide more accurate predictions for ground subsidence in similar coal mining areas.

Gas release from the crushed coal formation during coal mining poses a threat to the normal storage and gas transport within coal seam. This sort of release is largely related with the evolution of gas seepage properties of crushed coal, namely, the evolution of gas seepage properties plays an important role in the gas extraction and the outburst prevention of coal seam. Meanwhile, the evolution is directly related to the volume and geometry of fractures within the crushed coal and strongly influenced by particle size and porosity (axial displacement). In order to investigate the effect, a gas flow apparatus connecting with the MTS815.02 system was designed. The gas seepage properties of crushed coal specimens with five particle sizes of a (2.5–5 mm), b (5–10 mm), c (10–15 mm), d (15–20 mm) and e (mixed sizes) under the variable axial displacement of 10, 15, 20, 25, 30, 35, and 40 mm, respectively are measured by the revised MTS815.02 system. The results of test show that: The porosity decreases with the increase of axial displacement and the weight loss of larger particle size, respectively. Particle crushing during compaction is a main reason to increase small-size and emerge size 0–2.5 mm. Gas flow seepage properties of crushed coal are found to be strongly influenced by particle size and axial displacement. The permeability decreases and non–Darcy coefficient increases with the increase of axial displacement (decreases of porosity) and the decrease of larger particle size, respectively. The permeability and non-Darcy coefficient are controlled by the fracture among the coal particles. The seepage properties of crushed coal are not only related to particle size, loading levels (axial displacement), but also the compound mode. Based on the regression analysis, the relationship between the permeability and non-Darcy coefficient and porosity shows that the exponential function can fit the experimental data well.

A model accommodating multi-scale pores containing kerogen within an inorganic matrix is used to explore the complex multi-mechanistic transport mechanisms of shale gas reservoirs. These include the complex evolution of pressure, diffusion and flow within both kerogen and inorganic components and their interaction with effective stresses. A general poromechanical model is proposed considering desorption and molecular diffusion in the kerogen, viscous flow in the inorganic matrix and fracture system, and composite deformation of the triple porosity assemblage. The model is verified by history matching against field data for gas production rate. The simulation results indicate that the pattern of gas flow is sequential during gas depletion – pressure first declines in the fracture, followed by the inorganic phase and then in the kerogen. The evolution of permeability is pressure dependent and the evolution of pressure is closely related to the intrinsic gas diffusion coefficient in the kerogen, inorganic matrix intrinsic permeability and fracture intrinsic permeability. A series of sensitivity analyses are completed to define key parameters affecting gas production. The study shows that dominant influence of the fracture network in acting as the main permeable conduit. The intrinsic permeability and porosity of the fracture have a positive correlation with gas production, while fracture spacing has a negative correlation to gas production. Kerogen also plays a critical role in gas production for shale reservoirs with higher total organic carbon. The enhancement of inorganic matrix permeability and gas diffusion coefficient in kerogen could efficiently guarantee a long-term gas production with a higher rate.

To analyze the overlying strata movement law of recovering room mining standing pillars with solid backfilling. Physical simulation experiments with sponge and wood as the backfilling simulation material were tested. The results show that: (i) The covering-rock mechanics of the overly strata comes from “two-arch structures + hinged girder + bend beam” to “backfilling material + hinged girder + bent beam” by increasing the fill ratio from 0% to 85%, the beginning of overlying strata movement appears later and the total duration of subsidence velocity increased from zero to the highest value increases. The trend of “single polarization” of the subsidence velocity curves becomes noticeable and the velocity variation trend becomes stable. (ii) The equiponderate aeolian sand was added to improve the anti-pressure ability of the loess, and the corresponding ground processing & transportation system was designed. Keywords: Room mining standing pillars, Solid backfilling, Physical simulation experiment, Overlying strata movement

Based upon characteristic movement features of the overlying strata in solid backfill mining and in-situ observations, an associated model representing a roadway support system has been developed. Based on the Winkler foundation and beam model, the current study presents a static analysis of the model, thus permitting acquisition of a theoretical formula pertaining to roof convergence. Through use of working face 6304-1 (Jisan Colliery) as the research setting, the association between roof convergence magnitude and both packwall strength and width have been elucidated. Based upon observed conditions at the working face, realistic packwall parameters have been formulated, with numerical simulation results and field application results indicating that design parameters garnered from the developed formula successfully adapted to local geological movement and deformation. Accordingly, roadway deformation was shown to be within the permissible range, thus satisfying mine production requirements. The proposed method in the current study may give a design basis for pack design in the context of SBM under similar conditions. Keywords: Packwall design, Solid backfill mining, Roof convergence, Winkler foundation and beam model, Numerical simulation

China produces and consumes most of coal in the world. This situation is expected to continue within a certain period in the future. Currently, Chinese coal industry is confronted with several serious problems relating to land resource, water resource, environmental, and ecological sustainability. Coal resource exploitation causes the permanent fracture and movement of strata structure, which have caused the fracture and collapse of overlying strata and further led to the subsidence of ground surface as well as the seepage of water in aquifers around the coal seam, which has resulted not only in the loss of land and water resources, but also in serious threats and accidents to underground mining. On the other hand, mining and mineral-processing wastes are one of the world’s long plagued concerns among solid wastes. Coal gangue, as the major waste with a huge amount of discharge, has not only occupied the land, but has also contaminated the ambient land resources and hydrological environment, and further led to ecological system destruction and degradation. What is more, in China there are large amounts of coal—located under railways, buildings, and water bodies—which are unavailable with traditional mining methods. These problems are obviously threaten the concept of green sustainable development. This paper introduces a novel developed solid dense stowing mining method, which is able to significantly reduce or event eliminate the corresponding damages caused by underground mining behavior and realize green and sustainable development. The novelty of this research work is realizing the automation and synchronization of mining and material stowing with an appropriate compaction ratio for adequate support of goaf roof. It can improve the stability of rock strata and the safety and efficiency of underground mining. We also studied and designed a perfect stowing material by using coal gangue and fly ash with appropriate proportions under different particle size gradations. By implementation of the above-mentioned methods in China, the solid dense stowing rate of mined seam areas have reached more than 95% and the overburden strata movements have been reduced to extremely low level which had nearly no damages to above buildings. The solid dense stowing mining method has also realized the reuse and recycling of coal mine solid wastes. Meanwhile, considerable previously unavailable coal resources under buildings, railways, and water bodies have been made available for exploration, which could extend the life of coal mines and increase the sustainability for coal industry and the environment. Ultimately, this method is a reliable way to realize green and sustainable mining. The strata structure protection, the surface subsidence prevention, and coal mine solid waste disposal have been realized at the same time.

In solid backfill mining without gangue removal, the gangue is separated directly underground and backfilled into goaf. This necessitates the underground construction of an extra-large section chamber for separation equipments. For the construction of an extra-large section chamber in the Tangshan mine, we proposed an active support through a combination of bolting, anchor cables, lining, and a reinforced chamber floor by inverted arch pouring. ABAQUS software was used to analyze the surrounding rock deformation and the plastic zone development of the chamber under different excavation schemes. The best excavation scheme was determined, and the effectiveness of the combined supports was verified. In practice, the engineering installation showed good overall control of the movement of the surrounding rock, with roof-to-floor and side-to-side convergences of 154.6 and 77.5 mm, respectively, which meets the requirements for underground coal gangue separation. Keywords: Solid backfill coal mining, Extra-large section chamber, Effective support, Numerical simulation

Authors investigate the compaction properties of five materials that are commonly used in the solid backfill mining technique, obtaining stress–strain, bulk-ratio–stress and strain–time relationships for each of them. The results indicate that all five materials undergo three stages during the compaction process: fast compaction, slow compaction and steady compaction. Although the stress reached 20 MPa in the experiments, for all five materials, most of the deformation occurred below 2·5 MPa. Deformation under constant stress generally accounted for only 2·62–8·5% of the total deformation. The authors conclude that a tamping force of 1·5–2·5 MPa should provide sufficiently dense backfill of the gob. The results of these experiments could provide the basis for selection of solid backfill mining materials and for control of the bulk ratio and of late-stage surface subsidence, thereby ensuring secure mining under buildings, railways or water bodies.

s: Based on break characteristics of roofs in fully mechanized top-coal mining of thick shallow coal seams, a fracture mechanics model was built, and the criterion of crack propagation in the main roof was derived using the fracture mechanics theory. The relationships between the fracture length of the roof and the working resistance of the supports were discovered, and the correlations between the load on the overlying strata and the ratio of the crack’s length to the thickness of the roof were obtained. Using a working face of Jindi Coal Mine, Xing county Shanxi province as an example, the relationships between the fracture length of the roof and the working resistance of the supports were analysed in detail. The results give a design basis in hydraulic top coal caving supports, which could provide useful references in the practical application. On-site experiment proves that the periodic weighting step interval of the caving face is 15–16 m, which is basically consistent with the theoretical analysis results, and indicates that the mechanized caving hydraulic support is capable of meeting the support requirements in the mining of a super-thick but shallowly buried coal seam. Keywords: Super-thick shallow coal seam, Fully mechanized top-caving mining, Main roof, Fracture mechanics model0

This paper describes a specific case of mining in a water-rich coal seam in western China. Water inrushes, roof caving and other disasters induced by intensive mining operation could pose great threats to the safety of coal mines. The strata behavior during the high-intensity extraction in the water-rich coal seam is analyzed by employing the numerical simulation method and in situ monitoring. The results show that about 10 m ahead of the workface, the front abutment pressure peaks is at 34.13 MPa, while the peak of the side abutment pressure is located about 8 m away from the gateway with the value of 12.41 MPa; the height of the fracture zone, the first weighting step and the cycle weighting step are calculated to be 45, 50 and 20.8 m, respectively; pressure distribution in the workface is characterized by that the vertical pressure in the center occurs earlier and is stronger than those on both ends. Then, the results above are verified by in situ measurement, which may provide a basis for safe mining under similar conditions. Keywords: Coal seam under aquifer, Strata behaviors, High-intensity mining, Strata movement

Karst collapse pillar (KCP) is widespread in North China coalfields, where coal extraction above the Ordovician limestone aquifer is threatened by the abundant supply of water and a very high hydraulic pressure. KCP is composed of rock skeleton and fine fillings, which can be transferred under the effect of water flow, thus KCP usually functions as a channel for groundwater inrush. In order to investigate the mechanism of mining-induced groundwater inrush of KCP which was caused by fine fillings transfer, a self-designed particle transfer permeability testing system was used to test the crushed mudstones’ flow properties, which included fine filling particle transfer rate, porosity increase rate and permeability under the conditions of varying pore pressure, particle size mixture and compaction level (initial porosity). The tests indicate fine fillings transfer is the essential reason for mining-induced groundwater inrush (flow instability) of KCP. The flow properties changeability during fine particle transfer could be divided into four stages, i.e., initial flow stage, flow inrush stage, continued particle flow stage and stable flow stage, and flow inrush stage which is the key point to cause water inrush. Due to the crushing of edges and corners and the adjustment of the structure, the fluctuation of permeability–time relationship mainly distributed in the first two stages, which make a change to flow channel. Moreover, with the increasing of pore pressure, particle size mixture and initial porosity, the water inrush time and stable seepage time decreased more rapidly; the fine fillings, porosity and permeability increased gradually. The efficiency criteria analysis between measurement and calculation permeability shows an empirical equation can fit the relationship between porosity and permeability well, and not all of the pore structures were in flow; this means there was a part of pores that were invalid, but the effective porosity in flow can be treated as calculation value approximately.

The effectiveness of transmitting underground water in rock fractures is strongly influenced by the widths of the fractures and their interconnections. However, the geometries needed for water flow in fractured rock are also heavily controlled by the confining pressure conditions. This paper is intended to study the seepage properties of fractured rocks under different confining pressures. In order to do this, we designed and manufactured a water flow apparatus that can be connected to the electro-hydraulic servo-controlled test system MTS815.02, which provides loading and exhibits external pressures in the test. Using this apparatus, we tested fractured mudstone, limestone and sandstone specimens and obtained the relationship between seepage properties and variations in confining pressure. The calculation of the seepage properties based on the collection of water flow and confining pressure differences is specifically influenced by non-Darcy flow. The results show that: (1) The seepage properties of fractured rocks are related to confining pressure, i.e. with the increase of confining pressure, the permeability $$ k $$ decreases and the absolute value of non-Darcy flow coefficient $$ \beta $$ increases. (2) The sandstone coefficients $$ k $$ and $$ \beta $$ range from $$ 1.03 \times 10^{ - 18} $$ to $$ 1.53 \times 10^{ - 17} $$ m2 and $$ - 1.13 \times 10^{17} $$ to $$ - 2.35 \times 10^{18} $$ m−1, respectively, and exhibit a greater change compared to coefficients of mudstone and limestone. (3) From the regression analysis of experimental data, it is concluded that the polynomial function is a better fit than the power and logarithmic functions. The results obtained can provide an important reference for understanding the stability of rock surrounding roadways toward prevention of underground water gushing-out, and for developing underground resources (e.g. coal).

article i nfo This study hypothesizes that coal swelling is a heterogeneous process depending on the distribution of coal voids such as fractures, and that coal matrixes swell due to CO2 sorption while fractures are compressed in response. This explains why coal permeability reduces even when the effective stress on coal samples is kept constant. A dual porosity-dual permeability model, which separately accommodates gas flow and trans- port in the coal matrix (swelling component) and fracture systems (non-swelling component) and rigorously accommodates the role of mechanical deformations for a dual porosity continuum, was developed and ap- plied to prove this hypothesis. We use observations of a CO2 flow-through experiment on coal constrained by X-ray CT to define the hetero- geneous distribution of fracture porosity within the coal sample as a basis of mapping material properties for modeling. Matches between experimentally-measured and model-predicted ensemble permeabilities are ex- cellent. More importantly, the model results illustrate the crucial role of heterogeneous swelling in generat- ing swelling-induced reductions in permeability even when the fractured sample is mechanically unconstrained. These results prove that coal swelling is a heterogeneous process depending on the distribu- tion of coal voids: matrix (swelling component) swells while fractures (non-swelling component) are com- pacted in response.

When a coal sample is constrained either by displacements or by a confining stress, additional force and resulting stress develop within the coal. A simple “free expansion + push back” approach is developed in this work to determine the magnitude of this stress and its effect on permeability evolution. In this approach, the coal is allowed to expand freely due to gas sorption, and then it is pushed back by the applied effective stress to the original constrained conditions. The total “push-back” strains are used to calculate the change in coal permeability. This free expansion plus push back approach is applied to examine the variety of permeability responses observed in the laboratory and the veracity of their representation by theoretical models linking this behavior to gas sorption-induced swelling/shrinkage. These cases include (1) coal swelling tests under the uniaxial strain condition; (2) coal swelling tests under the displacement controlled condition; (3) coal swelling tests under the stress controlled condition. These responses are verified against other coal permeability models available in the literature and against experimental data and field data where few analytical solutions are currently available. In particular, this approach has led to a new coal permeability model that can be used to explain stress-controlled experimental observations. Stress-controlled swelling tests are normally conducted in the laboratory to characterize the evolution of coal permeability under the influence of gas sorption. Typically reductions in permeability are observed from gas-sorption-induced swelling even where effective stresses remain constant. This behavior remains enigmatic as the permeability of the porous coal is determined by the effective stress only. Our model is capable of replicating this apparently anomalous behavior.

The height of fractured water conducting zone is of significant importance for the safety of underground mining. Because of the conspicuous discrepancy of the height of fractured water conducting zone in Bulianta Coal Mine as predicted by the traditional method with those observed in practice, a systematic research has been carried out. The study indicates that two aspects should be taken into account. Firstly, the traditionally proposed empirical formula in prediction of the height of fractured zone was based on the conditions of single-slice mining where the mining height was less than 3 m and the total slice mining height was limited within 15 m. In such a case, it would not be suitable to predict the maximum fractured zone height for the conditions where a single mining height is larger than 3 m. Secondly, the stratum structure such as the thick and strong rock layer termed as key stratum plays an important role in controlling of the height of movement in the overburden. Physical model tests by making use of a similar material illustrate that if the vertical distance from the primary key stratum to the coal seam is shorter than a certain value, then the developing fracture zone will extend above the key stratum into the top of bedrock, resulting in a larger height of water conducting zone than is calculated by the empirical method. The outcome of the work presented will be helpful in practice to prevent the overburden aquifer inrush and to avoid mine water hazard.

In coal mining the water flow in broken rock is a very common phenomenon. Study of seepage properties of broken rock is one of the basic subjects required in order to understand the stability of rock surrounding roadways, preventing disasters such as water inrush and gas outbursts and developing underground resources. So far, quantitative studies on the nonlinear seepage properties of broken sandstone under different porosities are not extensive in the research literature. In this article, by means of an electro-hydraulic servo-controlled test system (MTS815.02) and a patent seepage device, the seepage properties under different conditions of porosity were tested on broken sandstone of five different grain sizes. Based on the loading method of controlling the axial compression displacement and steady permeating method, we obtained curves of the relation of pore pressure with time, as well as the relation curves between the pore pressure gradient for steady seepage and velocity. Furthermore, we calculated the permeability k and non-Darcy coefficient β corresponding to different porosities by fitting these curves with the binomial expression. This study indicates that: (1) the seepage properties of broken sandstone are closely related to grain size, load levels, and porosity structure; (2) the permeability k decreases, while the coefficient β increases with a decrease in porosity φ, but both the k − φ and the β − φ curves show some local fluctuations; (3) the permeability k of the broken sandstone has a magnitude of 10−14–10−12 m2, while the coefficient β ranges from 1010 to 1012 m−1. The results obtained provide some information for further study of the nonlinear seepage behavior of broken rock theoretically.

Stress-controlled swelling tests are normally conducted in the laboratory to characterize the evolution of coal permeability under the influence of gas sorption. Typically reductions in permeability are observed from gas-sorption-induced swelling even where effective stresses remain constant. This behavior remains enigmatic as the permeability of the porous coal is determined by the effective stress only. When these observations were interpreted, a matchstick or cubic coal model was assumed. Under this assumption, matrix swelling would not affect coal permeability because of the complete separation between matrix blocks caused by through-going fractures. This is why current coal permeability models have little success in explaining this inconsistency. It is generally believed that the reason for the failure is the inconsistency between the experimental conditions and the model assumptions. However, in this paper, it is considered that the reason may be the internal actions between coal fractures and matrixes have not been taken into consideration. In this study, a model capable of replicating this apparently anomalous behavior is developed. We consider the interactions of the fractured coal mass where cleats do not create a full separation between adjacent matrix blocks but where solid rock bridges are present. We accommodate the role of swelling strains both over contact bridges that hold cleat faces apart but also over the non-contacting span between these bridges. The effects of swelling act competitively over these two components: increasing porosity and permeability due to swelling of the bridging contacts but reducing porosity and permeability due to the swelling of the intervening free-faces. Under these conditions, a new permeability model is formulated. The new model is the key cross link that couples the multiphysics of coal-gas interactions. The formulation and incorporation of this permeability model into the multiphysics simulation of coal-gas interactions are presented in this paper.

Although coal–gas interactions have been comprehensively investigated, prior studies have focused on one or more component processes of effective stress in driving only isotropic changes in coal permeability. In our previous work ( Wu et al., 2009 ) a general porosity and permeability model was developed to represent the behavior of both the primary medium (coal matrix) and the secondary medium (fractures) under conditions of variable stress. In this study the permeability model is extended to define the evolution of gas sorption-induced permeability anisotropy under the full spectrum of mechanical conditions spanning prescribed in situ stresses through constrained displacement. These models are implemented into a fully coupled model of coal deformation, gas flow and transport in the matrix system, and gas flow and transport in the fracture system. The model separately accommodates compressible gas flow and transport in the coal matrix and fracture systems and rigorously accommodates the role of mechanical deformations for a dual-porosity continuum. Since mechanical interactions and the role of sorption-induced strains are rigorously accommodated, these micro-mechanical models are capable of following the evolution of porosity and permeability in both the coal matrix and the fracture network. This model represents important non-linear responses due to the effective stress effects that cannot be recovered where mechanical influences are not rigorously coupled with the transport system. The permeability model for fractures is verified against the analytical solution for a constant volume reservoir and applied to successfully match a suite of field data from the San Juan Basin. The fully coupled model for coal deformation and gas flow has been applied to quantify the impacts of fracture spacing and in situ ground stresses on coal properties and active processes: those involving shrinkage, swelling and direct changes in effective stress. Model results demonstrate the complex interactions of fracture–matrix induced by CBM production.

Although coal-gas interactions have been comprehensively investigated, most prior studies have focused on one or more component processes of effective stress or sorption-induced deformation and for resulting isotropic changes in coal permeability. In this study a permeability model is developed to define the evolution of gas sorption-induced permeability anisotropy under the full spectrum of mechanical conditions spanning prescribed in-situ stresses through constrained displacement. In the model, gas sorption-induced coal directional permeabilities are linked into directional strains through an elastic modulus reduction ratio, Rm. It defines the ratio of coal bulk elastic modulus to coal matrix modulus (0

A series of Ni 44− x Co x Mn 45 Sn 11 ( x =0, 1, 2) alloys were prepared by means of arc melting, magnetization curves under different temperatures were measured using vibrating sample magnetometer. The bicubic interpolations method was employed to calculate the magnetization M ( T , H ), and the magnetic entropy changes were figured out using the thermodynamic relation of magnetic materials. Results show that the values calculated based on the bicubic interpolation method are more accurate compared with those from conventional method, and the curves obtained are relatively smooth.

The series of Nb-poor Finemet-type alloys Fe 73.5 Si 13.5 B 9 Cu 1 Nb 3− x Al x ( x = 0, 0.1, 0.2, 0.4, 0.8 and 1.6) were prepared by partial substitution of Nb by Al and then were annealed at different temperatures under hydrogen protection. The effect of Al content as well as the annealing conditions on permeability spectra is discussed. It is found that (1) the initial permeabilities of the samples containing Al are greater than that of the samples without Al after isothermally annealing except for those annealed at 813 and 833 K, (2) the initial permeability (annealed at 793 K) of those containing a moderate amount of Al ( x = 0.1, 0.2, 0.4 and 0.8) are the greatest compared with those annealed at other temperatures, and (3) besides the Debye-type relaxation a new relaxation peak appears in μ ″– f curves and shows a tendency moving towards higher frequency with the increase of applied field amplitude, which is explained by using the domain wall motion theory in this paper. It is concluded that the initial permeability and relaxation permeability can be improved by moderate substitution of Nb by Al in Finemet type alloys and the initial permeability is dependent on the annealing temperatures. This research provides an innovative method for fabricating higher permeability soft magnetic materials at low cost; meanwhile, it is also significant in academic research.

The annealing condition, Al content, and field amplitude dependences of the complex permeability for Nb-poor Finemet type alloys, Fe 73.5 Si 13.5 B 9 Cu 1 Nb 3-x Al x ( x = 0, 0.5, 1.5, 2.0, and 3.0), were investigated using an impedance analyzer and X-ray diffraction. The results show that different Al contents lead to different optimum annealing conditions, and the Al content exerts a distinct effect on microstructure thus resulting in a variety of real permeability value. For the samples annealed at 793 K for 0.5 h, the real permeability increases with an increase in Al content when the Al content is below 2.0 at.%; as for those annealed at 793 K for 1 h and at 813 K for 0.5 h, an overall increase in real permeability can be obtained compared to those annealed at 793 K for 0.5 h. The permeability under different field amplitudes is also studied and it is found that the relaxation frequency in the lower frequency region tends to moving toward a higher frequency with an increase in field amplitude. All these might be because of the role of Nb in the annealing process and the solubility of Al in the amorphous matrix and nanocrystallized crystallites.

As mining activity rapidly develops to deeper and deeper ground, there have been an increasing number of groundwater inrush events occurring in China. The Ordovician limestone karst collapse pillar (KCP), which contains a lot of crushed rocks, usually functions as a channel for groundwater inrush. The factors, such as the geological conditions, groundwater flow and extraction percentage of coal seam in underground mines, are the main causes of recompaction and permeability change of crushed rock particles in KCP. The high permeability of rock will cause large volumes of groundwater flow, thus posing a great threat of loss of lives in the mines. It is important to take into account the compaction and seepage behaviors of the crushed rocks in Ordovician limestone KCP. The MTS815.02 system and a self-designed water flow apparatus were used to investigate the effect of particle size distribution on compaction and seepage behavior of crushed limestone particle mixture. The Reynolds number calculation of particle mixture shows that the seepage has been influenced by non-Darcy flow. Testing results indicate that the effective porosity of crushed limestone sample is strongly influenced by compaction and particle size distribution. The effective porosity decreases with the increase in compaction and decrease in larger particle size, respectively. Particle crushing during compaction is a main cause of size 0–2.5 mm materials, whereas some fine particles are washed away due to the effect of water seepage, which is a main cause of weight loss. Non-Darcy seepage properties of the crushed limestone are strongly influenced by compaction and particle size distribution. In general, during the compaction, the permeability decreases while the non-Darcy coefficient increases with the decreasing of effective porosity. The effective porosity, particle crushing and seepage properties of crushed limestone are not only related to compaction levels and mixture sizes but also to style of arrangement and initial pore structure.

Coal mining results in significant effects to the environment that include large mine voids, contaminated water, and solid wastes. To counter these negative effects this paper suggests a holistic approach (HMI) to clean coal energy management, which focuses on using modified mine waste as backfill materials to transform mine voids into seismic isolation, carbon sequestration, and energy storage facilities. HMI represents a next generation green mining technique and requires that mining operations and infrastructure management collaborate closely. This collaboration can be made easy using advanced IT technologies. A hypothetical HMI scenario for Xuzhou is presented.

Observations in the field demonstrate that there exist discrepancies between the differential movements predicted from theory and those experienced in practice. From the point of view of structural damage, such discrepancies should be eliminated in order to decrease subsidence damage associated with mining. Using non-linear geometrical field theory, the deformation factors are modified and the limitation of linear elastic theory is established. Only when the rotation angles are smaller than 4° is the application of conventional theory reasonable. A new deformation index, the mean rotation angle, is proposed. The study shows that there exists a relation between the mean rotation angle and the surface cracks. Incompatibility of rotation can initiate cracking. The outcome of the work presented will be helpful in improving the calculation accuracy of predicted differential movements, especially for steeper coal seam extraction, extraction under mountains, ‘top coal caving’ of thick seams, and mining in high relief areas.

Mining and mineral-processing wastes are one of the world’s largest chronic waste concerns. Their reuse should be included in future sustainable development plans, but the potential impacts on a number of environmental processes are highly variable and must be thoroughly assessed. The chemical composition and geotechnical properties of the source rock determine which uses are most appropriate and whether reuse is economically feasible. If properly evaluated, mining waste can be reused to reextract minerals, provide additional fuel for power plants, supply construction materials, and repair surface and subsurface land structures altered by mining activities themselves.

Harmonic wavelet had explicit functional expression, flexible time-frequency division, simple transforming algorithm and a finer frequency refinement function than the others wavelet. In this paper based on frequency distributing characteristic of nondestructive testing signal from rockbolt supporting system, the discrete harmonic wavelet transforming theory was used to get rid of the lower and higher frequency signal from the initial signal. Meanwhile, the reconstruction algorithm of harmonic wavelet was brought forward to gain the signal without the unnecessary bandwidth signals. Finally, a numerical signal and real signal which can de monstrate superiority of harmonic wavelet in filtering are presented, and the transforming result shows that it would make the system run more precise and stably in the detecting to the quality of rockbolt supporting system. Keywords: Rockbolt supporting quality, Testing, Harmonic wavelet, Filter 1. INTRODUCTION The testing method based on promulgating law of elastic wave had been widely used to the estimation of the rockbolt supporting quality[1,2]. The basic principle of above method was: make the rockbolt produce elastic vibration through putting on instantaneous dynamic load, then estimate the rockbolt supporting quality by the elastic wave response at the exposed end of the rockbolt[3~5]. During the testing course, for the disturbing from the testing equipment and environment, the testing signal would be polluted so that it brought great difficulty to the farther analysis and estimating. So it is very necessary to promote the quality of testing signal by filtering the unn ecessary disturbing signal. Compared with wavelets obtained from iterative approximation of multi-resolution, such as Daubechies wavelet(Daubechies, 1988), harmonic wavelet proposed by Newland (Newland 1993-1994), possess not only the advantages of usual wavelets but also the following features: (i ) there exist definite analytical expression to represent the wavelet function instead of complex iteration of scale function, (ii) time frequency decomposition of wavelet transform is more elastic without dyadic limitation, and (iii) the algorithm is simple and fast. At the same time, compared with other wavelets with definite analytical expression, harmonic wavelet has a favorable box-like spectrum. Many advantages of harmonic wavelet are discovered and it is used in the field of signal process, however, there are few papers devoted on filtering feature and filtering efficiency of harmonic wavelet. In this paper, in order to improving the quality of testing signal gaining from the rockbolt supporting system, harmonic wavelet is used to filter the disturbing signal. The excellent filtering wave character of harmonic wave may be shown from the dealing result of the simulation example and the real testing signal.