Investigation on Adhesion Strength of Thin Spray-On Liners in an Underground Coal Mine

A Thin Spray-on Liner (TSL) is defined as a chemically based layer or coating (3-5 mm) that is sprayed onto the rock surface to support mining excavations (Saydam and Docrat, 2007). Since the introduction, TSLs have received success in some applications in hard rock mines; however, their use has been slow in coal mining. The adhesion strength between a TSL and a rock surface is an important parameter controlling the design and performance of liner support systems. The in situ adhesion tests have been conducted to study the bonding between a TSL material and the coal substrate in an underground coal mine in NSW. A direct pull-off adhesion tester was adopted to conduct adhesion tests on the ribs of the roadway. In this paper, the in situ adhesion test results on coal substrate are analysed and presented

Numerically and Analytically Forecasting the Coal Burst Using Energy Based Approach Methods

Coal burst is referred to as the violent failure of overstressed coal, which has been recognised as one of the most critical dynamic failures in coal mines. This chapter aims to analytically and numerically evaluate the energy transformation between the different strata and coal layers. An accurate closed-form solution is developed. Due to the complexity of the causes and mechanisms contributing to the coal burst occurrence, 3D finite element modelling as well as discrete element models will be developed to validate the suggested analytical assessments of rock/coal burst occurrence. The energy concept is emphasised in order to improve the understanding of the underlying mechanisms of coal burst. Only with enhanced understanding of the driving mechanisms, a reliable coal burst risk assessment can be achieved

Design combined support under arbitrary impulsive loading

Rock bolts and cable bolts are usually considered to experience static loads under relatively low-stress conditions. However, in burst-prone conditions, support elements are subjected to dynamic loading. Therefore, it is important to understand cable bolt behaviour under dynamic loading conditions, particularly their energy absorption capacity. Rock bolts and cable bolts as well as steel mesh are widely used as permanent support elements in tunnelling, underground excavations and surface slope stability. This paper aims to determine the amount of the dissipated energy which can be taken into account to design combined yielding supports when subjected to dynamic loading. A ground support approach is suggested for underground excavations undertaking a range of mining-induced coal burst. A bench mark based on the largest expected impact loading is considered to conclude the level of coal burst risk and select an appropriate approach, whether quasi-static or dynamic, for the mine support

The environmentally induced corrosion failure of cable bolts in underground coal mines

The failure of cable bolts, made from high carbon cold-drawn steel wires, is frequently observed in underground coal mines. Hydrogen-induced stress corrosion cracking (HISCC) is known to be the main mechanism of such a failure. The groundwater and geomaterials (mixture of coal and clay) collected from the affected mines have not been found to be corrosive. In this study, we examine the effect of sulfate-reducing bacteria (SRB), which exist in affected mines, on the failure of cable bolts. We make stressed coupons from cable bolt wires and test the coupons in different solutions containing SRB. We find that the hydrogen sulfide produced by SRB promote hydrogen diffusion into the steel and causes HISCC while the steel is under constant load. The fractures in failed coupons show similar features to those failed in underground coal mines. This study provides insights into the role of microorganisms in the failure of underground structures. We recommend future studies to develop prevention measures to stop hydrogen diffusion into steel or microbial activities around the bolts

Floor heave monitoring using floor instrumentation

Several underground coal mines in Australia have recently reported and anticipated significant floor heave in gateroads during longwall retreat. Floor heave on longwall retreat is typically attributed to a stress notch. To further understand the mechanisms of floor heave, in situ floor heave monitoring was conducted using floor instrumentation at two coal mines. This paper provides the field monitoring results along with the process of selecting the instruments and monitoring sites. To grasp the whole picture of the deformation of floor strata, the instruments for both the vertical and horizontal movements of floor units were considered. For the horizontal floor deformation, the strain gauged shear strips were used in both mines. For the vertical displacement of floor units, a remote reading tell-tale (RRTT) was chosen in Mine A, while a GEL extensometer specifically designed for this floor monitoring was selected in Mine B. As Mine A had negligible floor heave at the monitoring sites, no significant movement of the floor was captured. Although the level of floor deformation was minimal, there were indications of bedding separations as the longwall face approached the sites. In Mine B, minor floor heave was observed at the monitoring location. The data from the instruments showed that the horizontal movement of the floor strata occurred greater than approximately 4 m below the floor surface which may suggest the depth of floor failure. While several practical issues were identified from the field studies, the field monitoring results facilitated better understanding of the failure mechanisms

A comparison of ESHAP with R-ESHAP chemotherapy regimen as mobilizing regimen in Hodgkin lymphoma and non-Hodgkin lymphoma patients

AMAÇ: Geçtiğimiz yıllarda lenfomaların tedavisinde büyük ilerleme gerçekleştirilmiştir. CD20 pozitif non-Hodgkin lenfomaların tedavisinde Rituksimab altın standart olmuştur. Mobilizasyon üzerine olan etkileri üzerine yeterli çalışma yapılmamıştır. YÖNTEMLER: 11 yıllık sürede ESHAP veya R-ESHAP ile mobilize edilmiş 84 Hodgkin lenfoma ve non-Hodgkin lenfoma hastasını değerlendirdik. BULGULAR: R-ESHAP rejiminin istatistiksel olarak ESHAP rejiminden daha az etkili olmadığını bulduk. SONUÇ: Aferez öncesi düşük trombosit sayısının oluşturduğu olumsuz etkiyi ESHAP rejimine rituksimab eklenmesi ortadan kaldırabilir. OBJECTIVE: In recent years great advance has been succeeded in therapy of lymphomas. Rituximab has become a gold standard of CD20 positive non-Hodgkin lymphomas. Its effects on mobilization have not been studied sufficiently. METHODS: We evaluated 84 Hodgkin lymphoma and non-Hodgkin lymphoma patients who were mobilized with ESHAP or R-ESHAP chemotherapy regimens in 11 years. RESULTS: We found out that R-ESHAP regimen was not significantly inferior to ESHAP regimen. CONCLUSION: Rituximab addition to ESHAP regimen may overcome negative effects of low platelet counts before aphaeresi

The optimisation of ground consolidation practices in longwall mining

The Australian longwall mining industry spends millions of dollars per year on both proactive and reactive ground consolidation methods from time to time across most of the underground operations currently in production. The design and effectiveness of the applications and products used are often variable and based on past experience at each site or what was considered successful at other sites in similar situations. This paper discusses the current product testing data and proposes an industry-standard testing regime that will provide mine site-based geotechnical engineers with a standardised set of data for product selection and geotechnical design. In addition, the preliminary results of an underground in situ testing program designed to provide quantitative data relating to the improvement in rock mass condition as a result of polymeric ground consolidation are presented and discussed. The results provide a measurement of changes in permeability, the material strength of the coal seam, and the migration of the injected material

A New Concept to Numerically Evaluate the Performance of Yielding Support under Impulsive Loading

The dynamic capacity of a support system is dependent on the connectivity and compatibility of its reinforcement and surface support elements. Connectivity refers to the capacity of a system to transfer the dynamic load from an element to another, for example, from the reinforcement to the surface support through plates and terminating arrangements (split set rings, nuts, etc.), or from a reinforcement/holding element to others via the surface support. Compatibility is related to the difference in stiffness amongst support elements. Load transfer may not take place appropriately when there are strong stiffness contrasts within a ground support system. Case studies revealed premature failures of stiffer elements prior to utilising the full capacity of more deformable elements within the same system. From a design perspective, it is important to understand that the dynamic-load capacity of a ground support system depends not only on the capacity of its reinforcement elements but also, and perhaps most importantly, on their compatibility with other elements of the system and on the strength of the connections. The failure of one component of the support system usually leads to the failure of the system

Analytical Procedure to Estimate the Horizontal Anisotropy of Hydraulic Conductivity in Coal Seams

The horizontal hydraulic conductivity anisotropy of coal seams is a controlling parameter for designing gas drainage boreholes. The ratio between the maximum and minimum horizontal hydraulic conductivity (RkH-kh) and the orientation of maximum horizontal conductivity defines this anisotropy in horizontal plane. This paper presents a new analytical procedure based on the field stress data and geometrical properties of coal cleats to calculate these two parameters. The application of this procedure for a real case in Eastern of Australia resulted in an average ratio of 20.9 for RkH-kh and orientation of NE for maximum horizontal conductivity. The comparison between these results with the measured values validated the accuracy of proposed procedure to estimate the anisotropy of horizontal hydraulic conductivity of coal seams