Faculty of Engineering, Built Environment and Information Technology
School of Engineering
Department of Mining Engineering
Selected Highlights from Research Findings
Road maintenance. The management of complex mine haul road maintenance is problematic, resulting in an increase in total road-user costs and reduction in service. A real-time maintenance management system is being developed to overcome these deficiencies. The system monitors road condition on a real-time basis through on-board vibration signature analysis, based on on-board truck diagnostic data collation, linked through a centralised communication and GPS backbone. To evaluate the feasibility of using these on-board truck diagnostic data in conjunction with truck location system utilities, a field trial was undertaken using an instrumented vehicle running on a prepared haul road containing a number of typical road functional defects.
From a preliminary assessment of the road defect vibration signatures, initially using vertical acceleration uniaxial waveforms only, it was possible to differentiate qualitatively between most road defect signatures. Based on the experiences of the field trial, an analytical model is being developed, which integrates on-board data acquisition. Feature extraction for individual sensors can then be integrated with a neural-based signature recognition algorithm using normalised data for speed, load and suspension characteristics. This will generate information regarding the specific road defect and its severity.
The real-time approach can also be adopted for a number of other situations, for example, a network of district roads where regular users, such as daily delivery services vehicles or maintenance supervisory personnel vehicles would be instrumented and information on vehicle position and road condition is relayed to or collated by a central maintenance dispatch system. By integrating truck and pavement interaction data as a basis for making road management-based decisions, a real-time system has the potential to manage maintenance as and where needed with resultant reduction in cost and improvement in service provided for road users.
Contact person: Prof RJ Thompson.
Basic principles for stable gullies in the gold and platinum mines of South Africa. Gullies are the vital in-stope excavations that provide access for mining personnel and material to, and mined ore from, the producing faces in the tabular hard rock mines. They pose a serious problem in most mines because they induce stress orientations, which, combined with blast damage, produce adverse rock fracture patterns that contribute to the loss of hangingwall and sidewall integrity. Rock-related injury statistics confirm this by highlighting gullies as the second highest risk area in South African hard rock mines. In certain gully geometries, poor blasting practice, and non-adherence to accepted standards worsen the problem.
The aim of this work was firstly to provide guidelines to select the correct gully geometry and appropriate support for a particular geotechnical environment, and secondly, to review the practical issues behind gully safety and stability. It was done by a literature review, underground observations, and an industry-wide survey of opinions on gully stability and implemented gully management practice. The underground survey covers observations from visits to 107 gullies situated in the respective geotechnical environments of the Basal Reef, Beatrix Reef, Vaal Reef, Carbon Leader Reef, Ventersdorp Contact Reef, Kimberley Reef, Kalkoenkrans Reef, Merensky Reef, and UG2 Reef. Despite the differing geotechnical conditions and gully geometries, common problems are experienced with geological structure, stress, and fracturing. Results from numerical modelling were also presented to help analyse the underground observations and to quantify the merits of the different gully layouts.
There are no really new techniques available to improve gully stability, but significant improvements in safety are attainable by employing the correct gully geometry for the geotechnical environment, good blasting practice, and appropriate support.
Contact person: Prof MF Handley.
Deformation in hard rock at great depth. Excavations in deep level hard rock mines show rheological or time-dependent deformation responses to mining-induced stresses. These are generally not as dramatic as those seen in soft rock environments, such as potash and salt mines, but the deformations can nevertheless become substantial in time. It is usual to see total excavation closure at a much earlier stage than predicted by numerical models, and real-time measurements underground have confirmed that closure takes place on a more-or-less continuous basis, with highest closure rates observed after a blast and then slowly diminishing with passing time.
The results of laboratory tests to determine the time-dependent response of hard rocks to loading were used to quantify these effects to explain the time-dependent phenomena observed underground. The primary intention of this work was to help explain the various time-dependant deformation processes around typical deep level hard rock tabular excavations. Three mechanisms were investigated in two typical hard rock types present in the deep level gold mines in South Africa, namely Ventersdorp Lava and Elsburg Quartzite. Uniaxial compression creep studies were done as the first part of the study followed by shear creep studies on discontinuities where crushed lava and crushed quartzite as well as a natural gouge were used as infilling. The last part of the study consisted of triaxial post-failure relaxation tests. The compression creep tests and the triaxial post-failure relaxation tests showed that the amount of energy dissipated by the lava is significantly less than for quartzite. For mines operating at depths greater than 2000m the implication is that the lava will show a greater rockburst-proneness than the quartzite. Since the lava shows a lower post-failure stress relaxation, it can store sufficient energy for multiple rockbursts, which is seen in the clustering of multiple seismic events in the deep level mines. The study provides the first data available for energy change calculations in fractured rock masses, and provides the first general indications for rockburst intensities ahead of active mining faces.
Contact person: Prof MF Handley.
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