Search

Twenty-seven specimens were tested to investigate the uniaxial compression behaviour of an innovative standing support for underground space applications. The innovative standing support consisted of an external fibre reinforced polymer (FRP) jacket and the infill column made of cementitious grout, tailings and coal wash rejects. Effects of the FRP layers number and water to the cementitious grout (w/g) ratio were evaluated. Test results indicated that lower w/g ratios produced stronger infill columns. With FRP confinement, the standing support demonstrated strain-hardening loading characteristics with a significant improvement in both strength and ductility. The highest strength and strain of the specimens achieved was 58.4 MPa and 11.8% respectively. Compared with the unconfined specimens, the confinement with four FRP layers increased the specimen strength and associated strain up to 3.6 and 27.0 times respectively. A correlation between the compressive strength of the infill material and the ultrasonic pulse velocity was also investigated. Furthermore, a simple design-oriented model was proposed to predict the peak strength and the corresponding strain of the innovative standing support.

Well-developed pores and cracks in coal reservoirs are the main venues for gas storage and migration. To investigate the multi-scale pore fractal characteristics, six coal samples of different rankings were studied using high-pressure mercury injection (HPMI), low-pressure nitrogen adsorption (LPGA-N2), and scanning electron microscopy (SEM) test methods. Based on the Frankel, Halsey and Hill (FHH) fractal theory, the Menger sponge model, Pores and Cracks Analysis System (PCAS), pore volume complexity (Dv), coal surface irregularity (Ds) and pore distribution heterogeneity (Dp) were studied and evaluated, respectively. The effect of three fractal dimensions on the gas adsorption ability was also analyzed with high-pressure isothermal gas adsorption experiments. Results show that pore structures within these coal samples have obvious fractal characteristics. A noticeable segmentation effect appears in the Dv1 and Dv2 fitting process, with the boundary size ranging from 36.00 to 182.95 nm, which helps differentiate diffusion pores and seepage fractures. The D values show an asymmetric U-shaped trend as the coal metamorphism increases, demonstrating that coalification greatly affects the pore fractal dimensions. The three fractal dimensions can characterize the difference in coal microstructure and reflect their influence on gas adsorption ability. Langmuir volume (VL) has an evident and positive correlation with Ds values, whereas Langmuir pressure (PL) is mainly affected by the combined action of Dv and Dp. This study will provide valuable knowledge for the appraisal of coal seam gas reservoirs of differently ranked coals.

Glioma is extremely difficult to be completely excised by surgery due to its invasive nature. Thus, chemotherapy still is the mainstay in the treatment of glioma after surgery. However, the natural blood-brain barrier (BBB) greatly restricts the penetration of chemotherapeutic agents into the central nervous system. As a front-line anti-glioma agent in clinical, carmustine (BCNU) exerts antitumor effect by inducing DNA damage at the O6 position of guanine. However, the therapeutic effect of BCNU was largely decreased because of the drug resistance mediated by O6-alkylguanine-DNA alkyltransferase (AGT) and insufficient local drug concentrations. To overcome these obstacles, we synthesized a BCNU-loaded hypoxia-responsive nano-micelle with BBB penetrating capacity and AGT inhibitory activity, named as T80-HA-AZO-BG/BCNU NPs. In this nano-system, Tween 80 (T80) serves as a functional coating on the surface of the micelle, promoting transportation across the BBB. Hyaluronic acid (HA) with active tumor-targeting capability was linked with the hydrophobic O6-benzylguanine (BG) analog via a hypoxia-sensitive azo bond. Under hypoxic tumor microenvironment, the azo bond selectively breaks to release O6-BG as AGT inhibitor and BCNU as DNA alkylating agent. The synthesized T80-HA-AZO-BG/BCNU NPs showed good stability, favorable biocompatibility and hypoxia-responsive drug-releasing ability. T80 modification improved the transportation of the micelle across an in vitro BBB model. Moreover, T80-HA-AZO-BG/BCNU NPs exhibited significantly enhanced cytotoxicity against glioma cell lines with high AGT expression compared with traditional combined medication of BCNU plus O6-BG. We expect that the tumor-targeting nano-micelle designed for chloroethylnitrosourea will provide new tools for the development of effective glioma therapy.

The lump-grout (LG) material consisted of coarse lumps and pumpable grout has been developed as an alternative infill material to cementitious grout (CG) material in secondary standing support for underground mines. This paper aims to further explore the compressive behaviour of the LG material under variable lateral confinements. A total of 30 LG specimens and 15 CG specimens, either under the active confinement via a Hoek cell or the passive confinement with a fibre-reinforced polymer (FRP) jacket, were prepared and tested. The main test variables included the confining pressure (i.e., 0, 2, 4, 6, 8, 12, 16 MPa) applied by a Hoek cell and the FRP jackets made of variable FRP composites (i.e., CFRP, GFRP and UHMWPE FRP). Test results demonstrated that both the compressive strength and the axial deformation of the LG material were obviously enhanced attributed to effective lateral confinement. The stress path independence assumption was also verified from this research, which provided a feasible access to build the relationship between the active- and passive confinement to the LG material. The in-depth comparison with the CG material, the LG material is much suitable as the infill material for the standing support, in terms of its cost-effectiveness and environmentally friendly.

This research reviewed the mechanics and gas desorption properties of intact coal, and tested the crushing work ratios of different intact coals, and then, studied the stress conditions for the failure or crushing of intact coal and the gas demand for the pulverization of intact coal particles. When a real-life outburst case is examined, the required minimum stress for intact coal outburst is estimated. The study concludes that the crushing work ratios of three intact coal samples vary from 294.3732 to 945.8048 J/m2. For the real-life case, more than 2300 MJ of transport work is needed, and 10062.09, 7046.57 and 5895.47 m3 of gas is required when the gas pressure is 1, 2 and 3 MPa, respectively. The crushing work exceeds the transport work and even reaches 13.96 times of the transport work. How to provide such an enormous crushing work is an energy-limiting factor for the outburst in intact coal. The strain energy is needed for the crushing work, and the required minimum stress is over 54.35 MPa, even reaching 300.44 MPa. These minimum stresses far exceed the in-situ vertical and horizontal stresses that can be provided at the 300–700 m mining depth range.

We propose that despite the general positive impact of maintaining political connections, internet utilization generates a disconnecting effect on the impacts of political connections on firm innovation. Using a unique survey dataset of Chinese private enterprises, the present study found that private firm owners’ internet use moderates the relationship between political connections and firm innovation. The present study therefore enriches the literature on the effects of political connections and resource-based view by discovering that internet technology disconnects firms’ political connections and substitutes for the function of political connections on information search and resource acquisition.

This paper presents the development of an innovative standing support for underground mines. The main feature of this standing support is its exterior container, a combination of polyvinyl chloride (PVC) with large rupture strain and fibre-reinforced polymer (FRP) with high strength-to-weight ratio. To demonstrate the advantages of this cementitious grout filled PVC-FRP tubular (PFT) standing support, a series of compression tests were conducted. Test variables included the strength of cementitious grout infill material and the thickness of FRP jacket. Compression tests were also conducted on cementitious grout-filled PVC tubular (PT) support and cementitious grout-filled FRP tubular (FT) support. These tests showed that PFT support presents a typical strain-hardening behaviour together with an outstanding axial deformation ability (>20% of the overall height of the support). In addition, the maximum compressive strength of PFT support is much higher than that of the corresponding PT support and FT support. Furthermore, using thicker FRP jacket or high strength cementitious grout material can enhance the load carrying capacity of PFT support. These comparative results indicated that the high performance of PFT support is mainly attributed to the combination of confining constituents (i.e. PVC and FRP) and infill material.

Chloroethylnitrosoureas (CENUs) are an important family of chemotherapies in clinical treatment of cancers, which exert antitumor activity by inducing the formation of DNA interstrand crosslinks (dG-dC ICLs). However, the drug resistance mediated by O6-alkylguanine-DNA alkyltransferase (AGT) and absence of tumor-targeting ability largely decrease the antitumor efficacy of CENUs. In this study, we synthesized an azobenzene-based hypoxia-activated combi-nitrosourea prodrug, AzoBGNU, and evaluated its hypoxic selectivity and antitumor activity. The prodrug was composed of a CENU pharmacophore and an O6-benzylguanine (O6-BG) analog moiety masked by a N,N-dimethyl-4-(phenyldiazenyl)aniline segment as a hypoxia-activated trigger, which was designed to be selectively reduced via azo bond break in hypoxic tumor microenvironment, accompanied with releasing of an O6-BG analog to inhibit AGT and a chloroethylating agent to induce dG-dC ICLs. AzoBGNU exhibited significantly increased cytotoxicity and apoptosis-inducing ability toward DU145 cells under hypoxia compared with normoxia, indicating the hypoxia-responsiveness as expected. Predominant higher cytotoxicity was observed in the cells treated by AzoBGNU than those by traditional CENU chemotherapy ACNU and its combination with O6-BG. The levels of dG-dC ICLs in DU145 cells induced by AzoBGNU was remarkably enhanced under hypoxia, which was approximately 6-fold higher than those in the AzoBGNU-treated groups under normoxia and those in the ACNU-treated groups. The results demonstrated that azobenzene-based combi-nitrosourea prodrug possessed desirable tumor-hypoxia targeting ability and eliminated chemoresistance compared with the conventional CENUs.

To investigate the bedding influence on coal mechanical behaviour in underground environments such as coal or rock burst, simulations of dynamic SHPB tests of pre-stressed coal specimens with different bedding angles were carried out using a particle flow code 2-dimensional (PFC2D). Three impact velocities of 4, 8 and 12 m/s were selected to study dynamic behaviours of coal containing bedding planes under different dynamic loads. The simulation results showed that the existence of bedding planes leads to the degradation of the mechanical properties and their weakening effect significantly depends on the angle θ between the bedding planes and load direction. With θ increaseing from 0° to 90°, the strength first decreased and subsequently increased and specimens became most vulnerable when θ was 30° or 45°. Five failure modes were observed in the specimens in the context of macro-cracks. Furthermore, energy characteristics combined with ultimate failure patterns revealed that maximum accumulated energy and failure intensity have a positive relation with the strength of specimen. When bedding planes were parallel or perpendicular to loading direction, specimens absorbed more energy and experienced more violent failure with increased number of cracks. In contrast, bedding planes with θ of 30° or 45° reduced the specimens’ ability of storing strain energy to the lowest with fewer cracks observed after failure. Keywords: Static–dynamic coupled loads, SHPB, Coal bedding angle, Strain energy, PFC2D

Coal burst is the violent failure of overstressed coal, and it is often accompanied by sound, coal ejection and seismic events. It is subsequently recognized as a serious safety risk of Australia after double fatalities coal burst happened at Austar Coal Mine. Considering the increasing trend of coal burst severity and frequency with mining depth, it is an urgent task to develop the coal burst risk assessment methods for Australia underground coal mines. Coal burst propensity index method is a widely used method of burst risk evaluation of coal as it is summed up from the coal burst research and practice of many countries. This paper presents the experimental and theoretical research of coal burst propensity index method for coal burst risk assessment in Australia. The definition of four indexes including elastic strain energy index (WET), bursting energy index (KE), dynamic failure time (DT) and uniaxial compression strength (RC) is introduced in the first part. Then, the standard laboratory test process and test parameter of coal burst propensity index is presented. DT test is conducted with 0.3 mm/min displacement control loading rate while other test is with 0.5 mm/min. Besides, modified data processing and risk classification method of test are proposed. Differentiate analysis of stress-strain curve is adopted in the data processing of DT and KE index. A four level risk classification form of burst risk is recommended for Australian underground coal mines. Finally, two likely improvement methods of WET test, including volumetric strain indicator method and theoretical calculation method, are discussed. Keywords: Coal burst, Coal burst propensity, Risk evaluation, Underground mining

Spontaneous combustion of residual coal in longwall goaf is a long standing hazard. Airflow leakage into goaf is a major driver to the hazard and this issue deteriorates where longwalls are operating in multiple seams and shallow covers because mining-induced cracks are very likely to draw fresh airflow into goaf due to presence of pressure differential between longwall face and surface. To study the problem more critically, a ventilation simulation package “Ventsim” is used to conduct a case study from Bulianta colliery. It was found that isolating and pressurizing active longwall panel can mitigate the problem and the pressure differential can be adjusted by varying performance of auxiliary fan and resistance of ventilation regulator. A booster ventilation system can also mitigate the problem by adjusting fan duties. Ventilation simulation is a powerful tool to study spontaneous combustion control in underground coal mine. Keywords: Ventilation simulation, Spontaneous combustion, Longwall operation, Pressure differential, Ventsim

Large scale open cut coal mining operations have significant impacts to groundwater in surrounding areas in both active and post-mining phases. The prediction of water inflows into a surface mine excavation is one of the many components involved in mine design phase. Groundwater performance also reacts to mining activities from the operational, economic and safety implications perspective. Under NSW planning legislation, as part of the comprehensive risk assessment, a groundwater impact assessment has to be conducted for a coal project to predict and mitigate the impacts in consideration of the government requirements. In this paper, the groundwater assessment modelling of mine pits was discussed in predicting of groundwater inflows and reviewing analytical and numerical approaches. A methodology of groundwater impact assessment for an open cut mine in NSW with a three-dimensional groundwater flow model Modflow Surfact demonstrated its functions in simulating the project’s impacts on the groundwater regime. The key findings with mitigations are discussed and recommended in the paper to reduce impacts on groundwater and fulfil regulation requirements in NSW. Keywords: Open cut coal mine, Groundwater impact assessment, Mining exposure area, Groundwater modelling methodology

The definition of “residual gas” can be found in different scenarios, such as the “fast” and “slow” desorption methods of measuring gas content and the sorption hysteresis test and gas management of coal mines, however, its meaning varies a lot in different contexts. The main aim of this paper is to discuss the existence of truly undesorbable residual gas in coal seam conditions and its impacts on sorption model and gas drainage efficiency. We believe the undesorbable residual gas does exist due to the observation of the extended slow desorption test and the sorption hysteresis test. The origin of undesorbable residual gas may be because of the inaccessible (closed or semi-closed) pores. Some gas molecules produced during coalification are stored in these inaccessible pores, since the coal is relatively intact in the coal seam condition, these gas molecules cannot escape during natural desorption and then create the undesorbable residual gas. Based on the existing adsorption models, we propose the improved desorption versions by taking into consideration the role of residual gas. By numerically simulating a gas drainage case, the gas contents after different drainage times are studied to understand the influence of residual gas content on gas drainage. The results indicate that the influence starts to be obvious even when the total gas content is at a high level, and the impact becomes more and more apparent with increasing drainage time. Our study shows that the existence of residual gas will impede the gas drainage and the total amount of recoverable coal seam methane may be less than expected. Keywords: Residual gas, Inaccessible pores, Desorption model, Gas drainage

Coal exhibits different creep behaviours when filled with different amounts of gas. Creep tests of coal filled with 0 and 0.5 MPa gas were performed, and strain under different axial stress was compared. The three creep constitutive models which were analysed using the method fitting experimental data for determining which creep model can reflect the creep process of the test best. The results show that the deformation of coal filled with 0.5 MPa gas is more higher than that of coal filled with 0 MPa gas under the same axial stress. Gas plays a positive effect on the deformation of coal process and will accelerate creep process. And gas will reduce coal intensity and change coal creep properties. Compared with Nishihara Model and Extensional Nishihara Model, Burgers Model can reflect the three stages of creep process of coal filled with gas better. The research results can contribute to reveal coal and gas outburst mechanism. Keywords: Coal, Gas, Creep, Constitutive model