Ernest Y Baafi

An evaluation of airborne laser scan data for coalmine subsidence mapping

The accurate mapping of coalmine subsidence is necessary for the continued management of potential subsidence impacts. The use of airborne laser scan (ALS) data for subsidence mapping provides an alternative method to traditional ground‐based approaches that affords increased accessibility and complete spatial coverage. This paper evaluates the suitability and potential of ALS data for subsidence mapping, primarily through the examination of two pre‐mining surveys in a rugged, densely vegetated study site. Data quality, in terms of mean point spacing and coverage, is evaluated, along with the impact of interpolation methods, resolution and terrain. It was assumed that minimal surface height changes occurred between the two pre‐mining surfaces. Therefore any height changes between digital elevation models of the two ALS surveys were interpreted as errors associated with the use of ALS data for subsidence mapping. A mean absolute error of 0.23 m was observed, though this error may be exaggerated by the presence of a systematic 0.15 m offset between the two surveys. Very large (several metres) errors occur in areas of steep or dynamic terrain, such as along cliff lines and watercourses. Despite these errors, preliminary subsidence mapping, performed using a third, post‐mining dataset, clearly demonstrates the potential benefits of ALS data for subsidence mapping, as well as some potential limitations and the need for further careful assessment and validation concerning data errors.

ARENA simulation model for truck-shovel operation in despatching and non-despatching modes

ABSTRACT Truck-shovel operation is a popular material handling system in surface mines because of its flexibility in removing large volume of earth material. In a typical mining operation, trucks are assigned to a shovel in either dispatching or non-dispatching mode. Using the “Expected Delay Time” concept, ARENA simulation models clearly show an improvement of mine productivity with a dispatcher, especially when the truck fleet size is around the optimum value.

Discrete event simulation of mining systems: Current practice in Australia

ABSTRACT Australia is a country rich with mineral resources and is home of a large number of mineral ventures in hard rock and soft rock areas. Eastern states have a concentration of coal mines and Western Australia have a number of gold, nickel, and iron ore mines. Use of simulation (discrete event) in modelling the mining systems is commonly used during mine design phases to evaluate various operational scenarios. System modelling has been limited to large companies with a good size of technical services staff. Routine evaluation of haulage systems is done in house using computer packages such as TALPAC. A review of some of the work that has been done in Australia is presented.

Modelling of groundwater recovery process for prediction of land settlement in surface mines

A two-dimensional finite element model was used to simulate the groundwater recovery process under various surface mining situations. The simulation results were used to predict the rate at which soil settlement takes place. It was found that the groundwater recovery process is very fast immediately after mine closure and cessation of dewatering programmes; a significant part of mine land settlement can be measured at such times. This paper presents a method for deriving the relationship between the re-establishment of the natural groundwater regime to its equilibrium position as existed prior to the commencement of mining operations and mine spoil settlement.

Computer simulation of complex dragline operations

ABSTRACT Large walking draglines are capital intensive pieces of equipment. To maximise the return on investment and to improve the performance of a dragline, its operation and influencing parameters must be understood and fully analysed with the view of optimising the process. Finding the normal working ranges for a given dragline and optimising its operation usually requires that various possible mining scenarios and pit configurations be assessed. This task is normally both difficult and time consuming and requires an analytical solution. This is ideally suited to the application of computer simulation methods. An integrated computer simulation model was developed to assist the mine engineer in planning dragline operations. The model uses a 3D geological modelling system to access the geological database. The model can simulate complex multi seam operations and different digging methods using a developed database. A generalised computer package, DSLX, is used to simulate various dragline digging method...

Application of Computational Fluid Dynamics (CFD) for Simulation of Acid Mine Drainage Generation and Subsequent Pollutants Transportation through Groundwater Flow Systems and Rivers

Faramarz Doulati Ardejani1, Ernest Baafi2, Kumars Seif Panahi3, Raghu Nath Singh4 and Behshad Jodeiri Shokri5 1Faculty of Mining, Petroleum and Geophysics, Shahrood University of Technology, Shahrood, 2School of Civil, Mining and Environmental Engineering, University of Wollongong, 3Shahrood University of Technology 4Nottingham Centre for Geomechanics, School of Civil Engineering, University of Nottingham, 5Faculty of Mining and Metallurgical Engineering, Amirkabir University of Technology (Tehran Polytechnic), Tehran 1,3,5Iran 2Australia 4UK

A simulation model to study bunching effect of a truck-shovel system

Abstract Bunching usually occurs when faster trucks and slower trucks are mixed in a truck-shovel mining system. This paper presents the development of discrete-event simulation model to estimate the impacts of bunching on the productivity and efficiency of a truck-shovel system. The bunching effect on production, BEP, is defined to estimate the production sensitivity to the bunching effect on the truck fleet. The simulation results show that the mixed truck fleets with varying performance can cause significant bunching effect if the hauling trucks are from multiple loading sites or dumps. Depending on whether the fleet is over-trucked or under-trucked, the bunching has significant impact on both the fleet productivity and the equipment utilisation. Furthermore, the fleet with higher BEP takes a priority of overtaking the fleet with lower BEP to increase the productivity.

Laboratory Tests on Thin Spray-On Liner Penetrated Rock Joints in Direct Shear

Thin spray-on liners (TSLs) are becoming more attractive as an effective mine roadway support medium in underground mines. The benefits of TSLs in stabilising the rock surface for underground mining roadways have been studied by some researchers (Tannant 2001; Stacey and Yu 2004; Mason and Stacey 2008; Ozturk 2012a; Nemcik et al. 2013). The fast setting TSLs can almost immediately support the excavations once applied onto the rock substrate. Stacey (2001) described some support mechanisms of TSLs and proposed the theory of ‘‘promotion of block interlock’’. The aim of this mechanism is mainly to maintain the rock mass in a stable condition by keeping the broken blocks in place and minimising block rotation. Ozturk and Tannant (2011) argued that rather than the mechanical interlocking, chemical reaction between the rock grain matrix and the liner material is more important to get higher adhesive strength. Stacey and Yu (2004) stated that the TSL penetration into the joints and fractures within the rock mass plays an important role in the supporting system. The depth of penetration of a TSL depends on its consistency, the sprayed pressure and the openness and orientation of the blasting-induced joints. For the less viscous TSLs, the penetration into the joints will be much greater. Mason and Stacey (2008) used the analytical method to study the effect of the penetration of TSLs into joints and fractures. The results revealed that the elastic modulus of fractured rock penetrated by liner material is the same as the elastic modulus of the rock without fractures. Fowkes et al. (2008) studied a crack repaired with TSLs and the results indicated that the crack filled with TSL material can prevent crack propagation and consequent failure. Ozturk (2012b) showed that edge crack propagation is the main failure mechanism during pull-off tests, although Fowkes et al. (2008) argued that cavitation being a cohesive failure of TSL resulting from growth and coalescence of micro-voids is likely the rupture mechanism of TSL adhesion tests. To study the shear behaviour of TSL penetrated rock joints, the direct shear test was adopted. The effects of surface roughness, penetrated thickness to asperity height ratio, shear rate, and normal load on the shear behaviour of TSL penetrated rock joints were investigated in this study.