While hazards resulting from spontaneous heating, gas migration, explosions and flooding remain a major threat to the safety and productivity of underground coal mines, specific research into overpressure ratings and integrity testing of ventilation control devices remains relatively limited.
“Given the difficulty to conduct field tests in operational environments, as well as the high variability of mine ventilation conditions, and gas generation rates, predicting the performance of underground ventilation control devices has posed a significant challenge for underground mines,” says Michael Salu, Principal Structural Engineer at PB.
In co-operation with ventilation control solutions manufacturer, Whitfield Minerals, Mr Salu has been engaged in a project to establish a computational engineering model to determine overpressure-rating compliance of VCDs.
With data obtained from live underground testing of Aquacrete VCDs, Mr Salu has been able to analyse explosion dynamics and the structural responses of full-size VCDs to establish precise ventilation device specifications.
While similar testing has been conducted at purpose-built facilities such as the Londonderry testing facility in New South Wales, Whitfield Minerals selected an underground mine in Western Australia, which allowed the use of higher blast pressures due to full underground confinement of the explosive testing. This enabled a wider range of tests to be completed and the results could be confidently extrapolated to ensure closer relevance to operational mines.
The blast test results were analysed and used to calibrate a 3-dimensional finite-element computer model of a VCD subjected to blast loading. This calibration began by transferring actual pressure distribution contours from the testing and then compared axial, bending and shear stresses as well as total loading and deflection between various configurations. The results were then used to develop a design tool that can assess the required thickness of a VCD for any combination of height, width, over pressure, head of water and factor of safety for any individual site location.
“Laboratory results, while intrinsically valuable, are frequently difficult to extrapolate to the mining environment and have proven to be limited in their success,” says Mr Salu.
The resultant computational model from the live blast testing, which is now utilised for Aquacrete’s shot blasted ventilation control devices, has been developed to form an integral part of the ventilation management plan of underground mines.
“The model not only aids the design of innovative ventilation management strategies but also provides ventilation officers with the assurance of knowing that their ventilation control devices not only comply with the most stringent industry regulations but increase the safety factor in underground mine environments,” says Mr John Whitfield, managing director of Whitfield Minerals.
The accuracy of the results has further enabled PB to provide engineering specifications regarding product selection, product thickness and required strength for each individual installation site. If an installation conforms to the specifications, structural engineering certification can be obtained from PB.
With more than 15 years as a specialist manufacturer of ventilation control solutions, Aquacrete has a well-earned reputation for research and innovative solutions in the Australian underground mining sector.
“Our technical services team has subjected our products to stringent product testing protocols over the years. In addition to live blast testing, our products have undergone tests to determine product strength, over-pressure ratings, fire resistance, diffusivity properties and water permeability ratings. They have exceeded the required standards in all tests and are widely specified by underground coal and metalliferous mines throughout Australia,” says Mr Whitfield.
The company’s flagship products, Aquacrete OPR2 and Aquacrete WetRepel, can be shot-blasted to any desired thickness in a single application without product slumping. The products do not need specialist installation, have a low toxicity level and reach a compressive strength of 13MPa in as little as 48 hours.
Whitfield Minerals is now concluding further studies into non-destructive testing protocols for installed ventilation control devices.