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This study focused on developing a risk assessment method for explosion at a coal reclaim tunnel (CRT) facility. The method was developed based on an analytical hierarchy process (AHP), which is an expert system that quantifies the factors of explosion incidents, based on events and hierarchies. In this paper, the proposed model was modification from original AHP model, specifically modifying the structure from ''alternative's results'' to ''total risk-rating's results''. The total risk-rating is obtained by summing up risk-rating of each factor, where the risk-rating is a multiplication product of the risk value by the AHP weighted value. To support decision-making using the expert system, data on the real conditions of the CRT were collected and analyzed. A physical modeling of the CRT with laboratory-scale experiments was carried out to show the impact of a ventilation system in CRT on diluting the methane gas and coal dust, in order to support the quantification of AHP risk value. The criteria to evaluate the risk of explosion was constructed from six components that are: fuel, oxygen, ignition, confinement, dispersion, and monitoring system. Those components had fifty-two factors that serve as sub-components (root causes). The main causes of explosion in CRT were found to be: mechanical ventilation failure and abnormal ventilation, breakdown of monitoring system, and coal spontaneous-combustion. Assessments of two CRT facilities at Mine A and Mine B were carried out as a case study in order to check the reliability of the developed AHP method. The results showed that the risk rating of Mine A was classified as high and Mine B was classified as medium, which is in a good agreement with the site conditions.

Tracer gas measurements have been carried out at the Pongkor underground gold mine, Indonesia, to evaluate mine ventilation flows and to investigate the effective turbulent diffusion coefficients in mine airways. The airflow routes and quantity, and the diffusion coefficient have been obtained by matching the measurements with numerical simulations using the advection-diffusion equation. Two leakages with flow quantity of 26.7 and 36.7 m 3 /s were detected. Reduction of leakages have been measured with the method after stopping the leakage routes. The turbulent diffusion coefficients for the simple airways have good agreement with the Taylor equation. However, for complex airways in operating mines, the coefficients show higher values (1.5 to 32 times) than that obtained by the Taylor equation and these have been compared with the data measured in the Kushiro coal mine, Japan. It is mainly affected by the ratio of airway length over equivalent diameter and airway frictions, but airflow mixing along the airway also has an effect on the diffusion coefficient.

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Diffusion of a solute in turbulent flows through a circular pipe or tunnel is an important aspect of environmental safety. In this study, the diffusion coefficient of turbulent flow in circular pipe has been simulated by the Discrete Tracer Point Method (DTPM). The DTPM is a Lagrangian numerical method by a number of imaginary point displacement which satisfy turbulent mixing by velocity fluctuations, Reynolds stress, average velocity profile and a turbulent stochastic model. Numerical simulation results of points' distribution by DTPM have been compared with the analytical solution for turbulent plug-flow. For the case of turbulent circular pipe flow, the appropriate DTPM calculation time step has been investigated using a constant β, which represents the ratio between average mixing lengths over diameter of circular pipe. The evaluated values of diffusion coefficient by DTPM have been found to be in good agreement with Taylor's analytical equation for turbulent circular pipe flow by giving β = 0.04 to 0.045. Further, history matching of experimental tracer gas measurement through turbulent smooth-straight pipe flow has been presented and the results showed good agreement.

Common problem in mining activity is instability caused by jointed rock mass. The strength of jointed rock masscan be increased by cement injection. An artificial rock sample made from dental plaster type of moldano tara isused in this study to evaluate the influence of cement injection to the strength of jointed rock sample. The roughnessof joint surface are obtained from the natural rock joints and divided into three groups of Joint RoughnessCoefficient (JRC) values based on Barton criteria. The injection materials are mixture of cement and water withthe ratio of water and cement of 4: 5 and 3: 2. This artificial samples are then subjected to direct shear tests. Thetest results are analyzed by Mohr-Coulomb criterion to obtain the cohesion and internal friction angle. It isrevealed that cohesion and internal friction angle increased for injected rock sample. The strength increase variesby JRC condition. For Sample with JRC value between 8-10, the study find that injection material with water tocement ratio of 4:5 is more effective than cement injection with ratio of 3:2. For JRC value between 12-14, 16-18,and 18-20, it is found that cement injection with ratio of 3:2 is more effective than 4:5.