This paper outlines the stability conditions at the Loy Yang Mine and the batter stability program. The purpose of the batter stability program is to manage the risk of instability of the operating and permanent batters within the Loy Yang Mine and waste dump. The program also meets the requirements of the relevant legislation and regulations. The program has been implemented to carry out an adequate level of geotechnical investigation and design analysis so that risks to operations can be assessed and managed. Two key indicators - groundwater levels within the batters and ground movement rates of the batters, are generally used to monitor permanent batter stability. These observations are used as the basis for determining the prevailing stability conditions of the permanent batters within the mine. Development of the Loy Yang Power Mine is resulting in significant ground movements. Horizontal and vertical movements, currently up to 1.4m at the mine crest, result from the relief of tectonic stresses due to the mine excavation. Regional subsidence is occurring as a result of aquifer depressurisation at Loy Yang Power Mine, but principally due to depressurisation at other sites. The ground movements are not adversely impacting on the surrounding area, including the Traralgon Township and long term movement trends indicate satisfactory conditions should continue.
Loy Yang Power Mine is located approximately 170 km east of Melbourne in the Latrobe Valley (Figure 1). The open cut Loy Yang Power Mine currently provides more than 30Mt of brown coal to the company's (Loy Yang Power Management Ltd) adjacent 4 × 500 MW power station units, 2 × 500 MW Edison Mission Energy power station units and a small dried coal plant operated by Auschar. The mine is currently 140m deep, which will increase to about 190m over the next 10 years.