No abstract

Many mines experience squeezing ground conditions due to orebodies located in weak rock masses. Often, the conditions leading to squeezing ground are not recognised or underestimated at the feasibility stage, leading to significant difficulties in mining the deposit, high costs and lost resources. There are a number of processes to determine the potential existence and degree of squeezing ground. Feasibility study to determine the rock mass behaviour will significantly reduce the risks associated with mining such deposits. In many cases, it is not possible to prevent squeezing occurring; however, good planning at the feasibility stage can provide the means to control the ground to allow economical extraction. The aim of this paper is to present an approach to maintain access development in squeezing ground identified during the feasibility study. Much is written about squeezing ground, but mainly about how to solve a problem that has already occurred (Potvin & Hadjigeorgiou 2008; Sandy et al. 2007). The aim of this paper is to give guidance for planning and management solutions for a deposit that will likely encounter squeezing ground conditions. The paper will also discuss operational requirements that need to be considered at the pre-production stage. The paper reviews ground control schemes aimed at controlling movement before and during stoping. It is based on experiences and research conducted at mines experiencing squeezing ground conditions and reviews considerations in design and monitoring to mitigate outcomes associated with squeezing rock masses. 2 Defining squeezing ground A number of definitions of squeezing ground are available. Potvin and Hadjigeorgiou (2008) listed a number of definitions as part of the Australian Centre for Geomechanics Squeezing Ground Task Force. Several of these are shown in Section 2.1. Section 2.2 describes how to recognise rock mass conditions that may lead to squeezing ground.

Kanowna Belle went underground from the open pit in 1996. At the start of 2000 the decline had reached 950 m below surface and stoping was down to 740 m. Seismicity was starting to occur and by May 2000 a seismic system had been commissioned. Since then, seismicity has played an increasing role in risk management of the mine, both in respect to safety and production. Seismic events with increased damage potential only started to occur mainly below 970 m depth (below C-block). The increase in seismic risk has lead to the development and implementation of the Garford yielding bolt, the development of seismic management systems and the adaptation of the mining method and sequencing. With increasing depth and seismicity, development of the lower E-block the mine is now moving into a new environment where new support systems and seismic control systems are being developed and implemented. This paper highlights the need for long term planning strategies, good quality seismic and geology data collection, analysis and recognition of high risk zones and subsequent management systems that involve planning, analysis, support, exclusion zones and education/communication of the work force.

No abstract