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The preparation of Al/Mg/Al laminated metal composites (LMCs) by lamination technique can well combine the good corrosion resistance of Al alloy and the lightweight characteristics of Mg alloy. In this paper, the atmospheric corrosion behavior and underlying mechanism of 6082/AZ31/6082 LMCs with and without side exposure for one year of filed exposure to the tropical marine atmospheric environment were investigated. The results showed that the corrosion rates of AZ31 and 6082 and LMC-C were 55.967, 1.167, and 0.925 g m−2·a−1, respectively. The microstructure of the Al layer on the surface of LMCs underwent a significant transformation, characterized by a noticeable grain refinement and a concomitant increase in dislocation density. Moreover, the potential disparity between the second phase (AlMnFeSi and Mg2Si) and the matrix was diminished. These findings collectively contribute to the enhanced resistance of 6082/AZ31/6082 LMCs to intergranular corrosion and pitting corrosion. However, the accelerated dissolution of the intermediate Mg layer, facilitated by the galvanic corrosion effect during field exposure of the LMCs, resulted in a 4.5-fold increase in corrosion-induced mass loss. Notably, the ultimate tensile strength of the LMCs exhibited insensitivity to field exposure duration, while their plasticity underwent a gradual decline. This comprehensive study elucidates the corrosion behavior and underlying mechanisms of 6082/AZ31/6082 LMCs subjected to a tropical marine atmospheric environment, providing valuable insights for the rational design and development of LMCs with enhanced comprehensive performance.

Acoustic-based technologies have attracted more attention in indoor ranging-based localization and tracking applications. To achieve high-accuracy ranging measurements, the precise identification of line-of-sight (LOS) acoustic signals is essential. This article proposes a novel off-online dynamic training (OODT) method to identify LOS acoustic signals from stream perspective based on a few training data in dynamic indoor environment. The dynamic online training method is proposed to identify the unlabeled acoustic feature stream by the parent–child model, utilizing the dynamic prior probability from time series information and a selection strategy based on the prediction risk. Then, the trustworthy pseudo-labeled streaming samples are accumulated into the child-models by online learning in real time. To reduce the impact of discarding the untrustworthy LOS signals, the off-online retraining method is proposed to incorporate the spatial information into the parent-models, which uses the category distribution of all pseudo-labeled streaming samples as the prior probability for iterative retraining. Subsequently, a new round of the dynamic online training is conducted to update the pseudo-labels of feature stream. Experiments demonstrate that the dynamic online training method has a higher identification precision of LOS acoustic signals from stream perspective, reaching 98% and more than 93.06% in above-ground and underground experimental scenarios. Moreover, the adaption for the concept drift is also verified with identification precision of 97.98% and 98.23%, respectively. The off-online retraining method further optimize the performance of the parent–child models in a single scenario. In conclusion, the proposed OODT method can autonomously identify dynamic acoustic signals with strong robustness and scenario drift adaptability.

The microstructures of cellulose nanocrystal (CNC) films grown from their aqueous suspensions are tuned by a shear flow during the formation of the films. The modulation of the chiral nematic organization of CNCs is visualized by the complete polarization analysis using Mueller matrix microscopy. Further optical simulation has ensured the comprehensive 3D structural analysis for the complex chiral structures of CNC films. As suggested by the optical investigation, regulating the helical structure under the shear flow involves two transition processes, an early in-plane unwinding, followed by a later helically vertical unwinding. We have also confirmed that sufficient shearing is required to reorient the helically aligned CNCs to form the nematic structure.

The evolution of artificial intelligence of things (AIoT) drastically facilitates the development of a smart city viacomprehensive perception and seamless communication. As a foundation, various AIoT nodes are experiencing low integration and poor sustainability issues. Herein, a cubic-designed intelligent piezoelectric AIoT node iCUPE is presented, which integrates a high-performance energy harvesting and self-powered sensing module viaa micromachined lead zirconate titanate (PZT) thick-film-based high-frequency (HF)-piezoelectric generator (PEG) and poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) nanofiber thin-film-based low-frequency (LF)-PEGs, respectively. The LF-PEG and HF-PEG with specific frequency up-conversion (FUC) mechanism ensures continuous power supply over a wide range of 10–46 Hz, with a record high power density of 17 mW/cm3at 1 g acceleration. The cubic design allows for orthogonal placement of the three FUC-PEGs to ensure a wide range of response to vibrational energy sources from different directions. The self-powered triaxial piezoelectric sensor (TPS) combined with machine learning (ML) assisted three orthogonal piezoelectric sensing units by using three LF-PEGs to achieve high-precision multifunctional vibration recognition with resolutions of 0.01 g, 0.01 Hz, and 2° for acceleration, frequency, and tilting angle, respectively, providing a high recognition accuracy of 98%–100%. This work proves the feasibility of developing a ML-based intelligent sensor for accelerometer and gyroscope functions at resonant frequencies. The proposed sustainable iCUPE is highly scalable to explore multifunctional sensing and energy harvesting capabilities under diverse environments, which is essential for AIoT implementation.

Ti particles (5 wt%) reinforced AZ91 Mg matrix composites (TiP/AZ91 composites) were prepared by powder metallurgy. As a result, the strength and ductility of TiP/AZ91 composites were improved compared with AZ91 alloy. The ultimate tensile stress (UTS) increased significantly from 163 MPa to 221 MPa, and the elongation increased from 3.5% to 10.9%. The YS and hardness decreased due to the slightly coarser grain size. The microstructural results showed that Ti particles were uniformly dispersed in the Mg matrix and the content of Mg17Al12was reduced, indicating that Ti particles can inhibit the precipitation of the second phase. The interface between Ti particle and Mg matrix showed that the Al3Ti layer was formed at the edge of the Ti particles. EBSD was used to analyze the twins and dislocations at different tensile strains. During the tensile deformation at room temperature, many tensile twins and dislocations formed in the TiP/AZ91 composites. The tensile twins and dislocations could coordinate plastic deformation, thus improving the elongation of the TiP/AZ91 composites.

Projection to latent structure (PLS) is a well-known data-based approach widely used in industrial process monitoring. Kernel PLS (KPLS) was proposed in prior studies to apply the PLS in the nonlinear process. However, KPLS-based methods only consider the nonlinear variation of the input and ignore that of the input and output simultaneously. Once the nonlinearity lies in inputs and outputs, the KPLS-based methods cannot accurately describe the nonlinear feature, and result in missing alarms. To provide a common monitoring approach for various nonlinear cases, an input–output KPLS (IO-KPLS) model is proposed. The proposed IO-KPLS maps both the original input and output variables into a high-dimensional space. A new nonlinear objective function is then established to extract latent variables. In addition, a nonlinear regression is designed to construct the IO-KPLS model. By constructing statistics, a complete quality-related process monitoring strategy is designed. Driven by the proposed strategy, the nonlinear feature between input and output can be efficiently extracted, and a comprehensive monitoring performance is provided. A numerical example and two industrial benchmarks are performed to demonstrate the efficiency of the proposed method.

ABSTRACTThe partial least squares (PLS) method has been successfully applied for fault diagnosis in industrial production. Compared with the traditional PLS methods, the modified PLS (MPLS) approach is available for slow-time-varying data processing and quality-relevant fault detecting. However, it encounters heavy computational load in model updating, and the static control limits often lead to the low fault detection rate (FDR) or high false alarm rate (FAR). In this article, we first introduce the recursive MPLS (RMPLS) method for quality-relevant fault detection and computational complexity reducing, and then combine the local information increment (LII) method to obtain the time-varying control limits. First, the proposed LII-RMPLS method is capable of quality-relevant faults detection. Second, the adaptive threshold leads to higher FDRs and lower FARs compared with traditional methods. Third, the adaptive parameter-matrices-based model updating approach ensures that the proposed method has better robustness and lower computational complexity when dealing with time-varying factors.

The effectiveness of rock bolting in ground control has been extensively investigated, mainly for resin based systems. Alternative coupling materials are needed to have good mechanical performance and to reduce the economic impact. This study proposed a new bolting system exploiting steel particles as coupling material. The applicability of this system was assessed by laboratory and field pullout tests, assisted by digital imaging correlation (DIC), infrared thermography (IRT) and acoustic emission (AE). The results indicated that, for a 20 mm diameter bolt, the suitable steel particle size and corresponding inner diameter of borehole were 1.4 and 28 mm, respectively. For bolts installed in steel tubes, the particles improved the loading capacity compared to the resin bonded ones. Additional pullout tests on cement blocks indicated that steel particles can be effective for hard rock, whilst resin was a better choice for bolting of soft rock. Similar understanding was obtained by pullout tests in engineering fields, which demonstrated that the steel particles coupled bolts can provide favorable effects in hard rock mass, while the effects were negligible when installed in extremely soft coal mass. The wide set of multi-technique measurements helped to understand the mechanisms involved in the performance of the bolting system with coupling steel particles.

It’s a universal engineering problem to seal micro-cracks of low-permeability argillaceous rock mass by grouting in the fields of civil engineering and mining. This paper achieved the grouting sealing of low- permeability artificial rocks with the permeability of 0.1–40 mD by adopting silica sol imbibition grouting. The variation characteristics of particle size, viscosity, and contact angle of silica sol during solidification and the pore size distribution of low-permeability artificial rocks were measured, and spontaneous imbibition tests of the artificial rocks were carried out. Finally, combined with the imbibition theory, percolation theory, and fracture medium grouting principle, the silica sol imbibition mechanism of low-permeability rocks and soil was discussed. The results show that: (1) Silica sol can be injected into artificial rocks with the minimum permeability of 0.1 mD through spontaneous imbibition; (2) The particle size increase of silica sol leads to decreased wettability, affinity, and injectability in grouting materials; and (3) In the range of 0.1–40 mD, the grout absorption first increases and then decreases with increased permeability. The number of large pores and fractures in the rock mass is related to injectability, and the number of small and medium pores is related to the internal driving force of imbibition. This study provides a theoretical basis for silica sol grouting sealing of low-permeability argillaceous rocks and is, therefore, an important reference for application.

Nowadays, additive manufacturing, or 3D printing (3DP), though not a new technology in many industrial fields, is still relatively novel in mining engineering. This study explored the application of 3D metal printing, 3D polylactic acid/acrylonitrile butadiene styrene printing, and 3D concrete printing in coal mining. Some examples of physical models established via 3DP technologies were studied in detail, namely, 3DP bolts, 3DP steel ladder beams, 3DP face plates, and 3DP metal arches, which were installed in scaled 3DP concrete prototype models of coal mine excavation. Through the comprehensive laboratory loading tests, the models could simulate the damage scenario highly similar to the real failures. The results show that the 3D printed physical models greatly improved the accuracy and reliability of experiments. On this basis, the conceptual design of a 3DP machine for physical models was proposed, which had the potential of resembling the strata deformation/collapse in natural scenarios. Through assessing the applicability of the additive manufacturing technology in mining engineering, this study aimed to further explore its potential applicability in other engineering contexts such as slope controlling, large underground engineering, and underground space stability. Applications of additive manufacturing in mining engineering research and accuracy of the additive manufacturing provide opportunities to improve the knowledge of 3D printing for mining engineering.

Air pollution is a serious problem. Refractory thiophene sulfides, which cause air pollution, bring great challenges to their rapid and accurate identification. In this work, we propose a fluorescent sensor array based on two perovskite nanocrystals (CsPbBr3NCs and CsPbBr3/SiO2NCs) to distinguish different thiophene sulfides. The hydrogen bonding force between the thiophenics of thiophene sulfides and the amino groups of the perovskite NCs results in the weakening of the fluorescence signals of the perovskite NCs. The diverse interactions between thiophene sulfides and two perovskite NCs provide rich information, which can be obtained on the sensor array and identified by linear discriminant analysis. Five thiophene sulfides (i.e., benzothiophene, dibenzothiophene, 2-methylbenzothiophene, 3-methylthiophene, and thiophene) were discriminated by the sensor array at concentrations of 10–50 ppm. The effectiveness of the sensor array was further verified in the discrimination of blinded samples, in which all 10 samples were correctly identified. In addition, it is gratifying that even binary mixtures of thiophene sulfides could be distinguished by the proposed sensor array.

As an essential part in the toolbox of super-resolution microscopy, stimulated emission depletion (STED) nanoscopy has been widely explored in revealing the substructure and bioactivities in fluorescence imaging. Among the applied STED fluorophores, silicon-substituted rhodamines (SiRs) belong to one of the most extensively employed fluorophores. The carboxy-SiR was favored in STED bioimaging with many advantages, including reliable photostability, cell permeability, tunable fluorogenicity, feasible structural decoration and so on. We reviewed the research of carboxy-SiR in the STED nanoscopy and hopefully this can inspire more efforts in the design and application of STED fluorophores.

Conductive polymers have been intensively investigated as materials for electrodes in flexible electronics due to their favorable biocompatibility and reliable electrochemical stability. Nevertheless, patterning of conductive polymers for the fabrication of devices and in various electronics applications confronts multifarious limitations and challenges. Here, we present a simple but efficient strategy to obtain conductive polymer microelectrodes via utilization of surface-tension-confined liquid patterns. This method shows universality for various oxidizers and conductive polymers, high resolution, stability, and favorable compatibility with different surfaces and materials. The developed method has been demonstrated for creating conductive polymer microelectrodes with a customized reaction process, defined geometry, and flexible substrates. The obtained microelectrodes were assembled into flexible capacitive sensors. Thus, the method realizes a facile approach to conductive polymer microelectrodes for flexible electronics, biomedical applications, human activity monitors, and electronic skin.

Steel and polypropylene hybrid fiber-reinforced concretes have been widely considered for structural applications due to its superior mechanical performance compared to plain and mono fiber-reinforced concretes. Fire is one of the most serious potential risks to concrete structures. The fire resistance of the steel and polypropylene hybrid fiber-reinforced concretes cannot be ignored when assessing the safety of concrete structures. This paper reviews the available studies on the mechanical performance of thermally damaged steel and polypropylene hybrid fiber-reinforced concretes. The deterioration mechanism and the influence of the test factors were discussed. The temperature-dependent mechanical properties of the hybrid fiber-reinforced concretes were analyzed, including compressive elastic modulus, compressive strength, flexural strength, and fracture toughness. In addition, the effect of the post-fire re-curing on the mechanical performance of the thermally damaged steel and polypropylene hybrid fiber-reinforced concretes was also reviewed.

Controllable rock cracking technology is crucial for the exploration and exploitation of deep underground resources. Many existing studies have been dedicated to the laser-assisted rock-weakening technology. It has been proved that laser irradiation can improve drilling and blasting efficiency when combined with mechanical rock fracturing methods, which are irrelevant for borehole stabilization. To improve the latter, this study used laser ablation for borehole reinforcement. The high-power laser was applied to typical rock samples (sandstone, mudstone and coal) in both dry and saturated conditions. Multi-technique observations and measurements were used to fully understand the peculiar modifications of the specimens under laser treatment, i.e. mechanical loading, acoustic emission (AE) monitoring, digital image correlation (DIC) strain field evaluation, infrared thermography (IRT) monitoring and X-ray computed tomography (CT) scanning. The results showed that, in addition to the effects already demonstrated, laser irradiation can improve the strength of the soft rock, especially in the saturated state. The process involved a complicated phase change including melting and evaporation of the matrix under high-temperature and high-pressure to form a glassy high strength silicate material. This process is similar to the reaction between molten lava and water, or the impact of an asteroid on the earth. Inspired by the results, a conceptual path for a new borehole stabilization technology using laser ablation was outlined.

Hairy cell leukemia (HCL) is an infrequent and persistent B-cell inert lymphoid leukemia. In this study, we present the case of a 71-year-old female patient with a previous diagnosis of variant HCL who experienced a severe herpes zoster infection leading to an extensive skin eruption. The patient’s initial diagnosis of HCL occurred 7 years ago, and she underwent treatment with cladribine, interferon, COP (cyclophosphamide, vincristine, and prednisone), benztropine tablets + clarithromycin dispersible, and ibrutinib. Immune disorders resulting from repeated prior chemotherapy and targeted therapy may potentially precipitate herpes zoster infection. Despite an initial two-week period of unresponsiveness to antivirals and nerve nutrition treatments, the introduction of topical Coptis liquid to the treatment regimen yielded significant efficacy. This case report underscores the potential of Chinese medicine as an adjunct to conventional antiviral therapy in the management of herpes zoster infection in immunocompromised patients. This treatment protocol has the potential to enhance efficacy, enhance quality of life, and serve as a more robust foundation for clinical diagnosis and improved treatments.

Asphalt pavements are inevitably affected by coupled effects of dry-wet/freeze-thaw cycles, UV radiation, temperature, and loading during service, resulting in degradation of their road performance and reduced service life. Therefore, this study used crumb rubber (CR) and polyphosphoric acid (PPA) as modifiers to prepare CR/PPA composite modified asphalt mixtures for testing. To investigate the mechanical properties of the composite modified asphalt mixtures under the action of multi-factor coupling. Meanwhile, the performance analysis of matrix asphalt and SBS modified asphalt mixtures were carried out as a comparison. Density and water penetration tests, splitting tests, beam bending tests, and four-point bending fatigue tests reveal the evolution of asphalt mixture road performance. Finally, regression fitting was performed on the test data to establish the mechanical damage model of each type of asphalt mixture. The results show that with the increase of wet-dry/freeze-thaw cycles and the increase of UV radiation time, the void ratio and water permeability coefficient increase and the splitting strength, bending and tensile strain, and fatigue life decrease for all types of asphalt mixtures. When the number of wet-dry/freeze-thaw cycles reached 8, the mechanical properties of the asphalt mixture decreased significantly, while the changes leveled off after the number of cycles reached 15. When the UV radiation time is less than 4 months, the mechanical properties of the asphalt mixture decay more slowly. However, with a further increase in radiation time, the mechanical properties decay rapidly. The water-saturated specimens have a more significant effect on the mechanical damage of each type of asphalt mixture. Compared with the other two mixtures, the composite modified asphalt mixtures have superior mechanical properties and fatigue life. The mixture performance damage model based on the least squares Levenberg-Marquardt method (L-M method) was able to simulate the experimental data well, with a minimum correlation coefficient R2of 0.9285. In summary, the road performance of all types of asphalt mixtures under the coupling of multiple factors has deteriorated, while the composite modified asphalt mixtures have better anti-damage characteristics, with good prospects for promotion.

The paper is a summary of discussions on four topics in rockburst and dynamic ground support. Topic 1 is the mechanisms of rockburst. Rockburst events are classified into two categories in accordance with the triggering mechanisms, i.e. strain burst and fault-slip burst. Strain burst occurs on rock surfaces when the tangential stress exceeds the rock strength in hard and brittle rocks. Fault-slip burst is triggered by fault-slip induced seismicity. Topic 2 is prediction and forecasting of rockburst events. Prediction for a rockburst event must tell the location, timing and magnitude of the event. Forecasting could simply foresee the probability of some of the three parameters. It is extremely challenging to predict rockbursts and large seismic events with current knowledge and technologies, but forecasting is possible, for example the possible locations of strain burst in an underground opening. At present, the approach using seismic monitoring and numerical modelling is a promising forecasting method. Topic 3 is preconditioning methods. The current preconditioning methods are blasting, relief-hole drilling and hydrofracturing. Defusing fault-slip seismicity is difficult and challenging but has been achieved. In very deep locations (>3000 m), the fracturing could extend from the excavation face to a deep location ahead of the face and therefore preconditioning is usually not required. Topic 4 is dynamic ground support against rockburst. Dynamic ground support requires that the support system be strong enough to sustain the momentum of the ejecting rock on one hand and tough enough on the other hand to absorb the strain and seismic energies released from the rock mass. The current dynamic support systems in underground mining are composed of yielding tendons and flexible surface retaining elements like mesh/screen and straps. Yielding props and engineered timber props are also used for dynamic support.

Abstract Discord search is an important technique for time series analysis, especially for anomaly detection. In recent years, many computational approaches of discord search were studied; however, limitation exists while only the problems with univariate time series data can be well addressed. In this study, we proposed a novel computational framework to identify discords from multivariate time series (MTS) data, namely, LRRDS (Local Recurrence Rate based Discord Search). LRRDS accurately identifies the discords by analyzing a recurrence plot, which is transformed from the original time series data. An innovative strategy was employed to improve the efficiency for pair-wise distance comparison of two subsequences. In the experimental simulations, LRRDS was applied to an extensive number of MTS datasets. Results show that the proposed approach is more efficient than existing methods, such as GDS. In conclusion, the LRRDS approach solves the adaptability problem of discord sequences in multi-dimensional space and guarantees the computational effectiveness and efficiency. [ABSTRACT FROM AUTHOR]

AbstractSandstone is a typical sedimentary rock. Chemical corrosion can accelerate the development of damage and reduce the strength of sandstone. An elastoplastic damage model considering the coupled chemo-mechanical damage is proposed to describe short-term mechanical behaviour of sandstone after immersing in the chemical solution. In the first part, the coupled damage variable is defined based on the analysis of chemical damage mechanism. In the second part, based on the framework of irreversible thermodynamics, the general formulation of the phenomenological model is presented. The model considers the effect of initial chemical damage on the evolution of mechanical damage. It can also describe the coupling between plastic deformation and mechanical damage. Meanwhile, a non-associated rule is chosen in order to describe the compression–dilatation transition of volumetric deformation. Comparisons between numerical simulations and experimental data show that the model is able to describe the main mechanical behaviour of sandstone under chemical corrosion.

Generalized eigendecomposition problem has been widely employed in many signal processing applications. In this paper, we propose a unified and self-stabilizing algorithm, which is able to extract the first principal and minor generalized eigenvectors of a matrix pencil of two vector sequences adaptively. Furthermore, we extend the proposed algorithm to extract multiple generalized eigenvectors. The performance analysis shows that only the desired equilibrium point of the proposed algorithm is stable and all others are (unstable) repellers or saddle points. Convergence analysis based on the deterministic discrete-time approach shows that, for a step size within a certain range, the norm of the principal/minor state vector converges to a fixed value that relates to the corresponding principal/minor generalized eigenvalue. Thus, the proposed algorithm is a generalized eigenpairs (eigenvectors and eigenvalues) extraction algorithm. Finally, the simulation experiments are carried to further demonstrate the efficiency of the proposed algorithm. [ABSTRACT FROM PUBLISHER]

Currently, bolt-support technology is commonly applied throughout the world during mining activities, civil engineering, and hydraulic projects. The theory of a pretensioned and fully bonded bolting system has long been proposed for use as tunnel supports; however, this technology is difficult to implement in coal mining, particularly for roadways that require immediate support. In this study, a modified cement with water-to-cement ratio of 0.25 was used to work in tandem with a traditional resin cartridge to create a pretensioned, fully bonded bolting system. The fast-setting epoxy resin is positioned at the bottom of the borehole for pretension, and the cement is positioned along the rest of the borehole for full-length bonding along the bolt. Based on a series of pullout tests on the proposed bolting system with different pretension forces, this study shows that a pretensioned, fully bonded bolting system is more durable and stable than the end-encapsulated resin bolting system that is currently utilized in most of China’s coal mines. Additionally, an acoustic emission detection test was simultaneously conducted to further describe the inner fracture mechanisms of the bolting system under different pretension forces ranging from 50 to 140 kN, with an increment of 30 kN. The results of this test indicate that a higher pretension force can decrease the damage events in the bolting system. Additionally, the failure form of a pretensioned, fully bonded bolting system is more likely to be dominated by the fracture of the bolt rod in most circumstances. Finally, this combined bolting technology is successfully implemented in a coal mine, and the monitored results confirm that the proposed bolting measure is effective and reliable.

This paper proposes a novel coupled neural network learning algorithm to extract the principal singular triplet (PST) of a cross-correlation matrix between two high-dimensional data streams. We firstly introduce a novel information criterion (NIC), in which the stationary points are singular triplet of the crosscorrelation matrix. Then, based on Newton's method, we obtain a coupled system of ordinary differential equations (ODEs) from the NIC. The ODEs have the same equilibria as the gradient of NIC, however, only the first PST of the system is stable (which is also the desired solution), and all others are (unstable) saddle points. Based on the system, we finally obtain a fast and stable algorithm for PST extraction. The proposed algorithm can solve the speed-stability problem that plagues most noncoupled learning rules. Moreover, the proposed algorithm can also be used to extract multiple PSTs effectively by using sequential method.

This study investigates the stability problem of gob-side entry retaining (GER) and backfilling wall which located under the key block B. Based on the combined research of elastic–plastic mechanics, structure mechanics and modern theory of mining-induced pressure, the caving characteristic and roof structure over the GER were analyzed, and the vertical force and the torque on retained entry roof were also derived as the position for the retained entry varies. On the basis of the specific geology in Huainan mining area, the results indicate that a relatively more stable position for retained entry neighbors the hinge point of block A and B, and it also located at a scope ranging from this point to the one-third length of block B in horizontal direction. As to appropriate position for backfilling wall, this study recommends partial-road-in backfilling method for GER. Field trial conducted at panel face 12418 of Xieqiao Mine demonstrates that the recommended width for original entry is 3.6 m and the preferred width proportion between original retained entry and original entry is 75 % or so whereas the avoidable one is 88 % or so. These findings provide qualitative references to the mines which share similar geology as what Huainan mining area characterized.

Retaining gob-side entryways and the stability of gas drainage boreholes are two essential techniques in the co-extraction of coal and gas without entry pillars (CECGWEP). However, retained entryways located in deep coal mines are hard to maintain, especially for constructing boreholes in confined spaces, owing to major deformations. Consequently, it is difficult to drill boreholes and maintain their stability, which therefore cannot guarantee the effectiveness of gas drainage. This paper presents three measures for conducting CECGWEP in deep mines on the basis of effective space in retained entryways for gas drainage. They are combinations of retaining roadways and face-lagging inclined boreholes, retaining roadways and face-advancing inclined boreholes, and retaining roadways and high return airway inclined boreholes. Several essential techniques are suggested to improve the maintenance of retained entryways and the stabilization of boreholes. For the particular cases considered in this study, two field trials have verified the latter two measures from the results obtained from the faces 1111(1) and 11112(1) in the Zhuji Mine. The results indicate that these models can effectively solve the problems in deep mines. The maximum gas drainage flow for a single hole can reach 8.1 m3/min and the effective drainage distance can be extended up to 150 m or more.