Ernesto Villaescusa, Professor of Mining Geomechanics from the West Australian School of Mines (WASM), explains that “as underground mining proceeds to depths approaching 1,000 m, the ratio of intact rock strength to induced stresses around conventional development excavations is such that failure of the rock mass adjacent to the excavations can occur very soon after construction.

“At the present time, such conditions have led to the abandonment of operations that have reached those depths, leading to losses of hundreds of millions of dollars. However, over the next two decades, when the moderate depth resources are likely to be depleted, those conditions will be faced routinely.

“In Western Australia, this problem is exacerbated with the implementation of top-down extraction strategies, in which ramp access for truck haulage is required leading to excavation size exceeding 6 m x 6 m (not including turn-outs). For this situation, widespread damage has been experienced for most conditions when the depth approaches or exceeds 1,000 m below surface. This is threatening our ability to mine the next 1,000 m – that is from 1,000 to 2,000 m, where a large part of the future resources are located.”

Through CRCMining Villaescusa has been undertaking research in deep excavation stability at WASM. By being familiar with current technology developments and gaps he is trying to shape future developments in deep mining.

Over the last two years he and his research team have undertaken fundamental laboratory experiments at the WASM site in Kalgoorlie and established a hypothesis regarding the on-set of damage leading to pillar crushing and total excavation collapse in deep underground mines – typically these failures include violent wall spalling.

From July 2015, a new three-year project is proposed to deliver field-based research where excavation shapes designed to account for the large vertical stress components are constructed, and where large energy dissipation ground supports are immediately installed.

In the process, de-stress blasting for development blasting will be studied in detail and the understanding of the key variables formalised. The depth of the excavation disturbance with and without de-stress blasting will be defined, and used to design effective ground support strategies. The role of geological structures, blast damage and orientation of the induced stress will also be considered.

A computer program will also be used to study the interaction of induced stress, with conventional development blasting, as well as a number of de-stress blasting strategies. In parallel, the research team will work on geotechnical instrumentation devices that will be capable of providing warning of the progressive loading on high energy dissipation reinforcement and the implication for violent failure around the excavation boundaries.

This research will test an excavation damage hypothesis and create a global methodology for safe and economic development at depths not yet reached by the current mining operations. It will enable the sustainability of underground mining even in conditions of very high stress, where failure can occur very soon after the construction of the underground openings.

Successful completion of this research will allow Western Australia to remain the leader in underground mining development. That is, development that is safe from the point of initial construction to the life of mine completion – even at great depth.

For more information visit CRC Mining website www.crcmining.com.au or contact Professor Ernesto Villaescusa [email protected]