Guidelines for Assessment of Geotechnically Safe and Stable Post-Mining Landforms

The purpose of this project was to develop a guidelines document as a step along the path to a common understanding of the requirements for, and limitations of, assessment of long term geotechnical safety and stability. The intent is to provide a certifiable process for the preparation and delivery of geotechnical assessment reports that are undertaken by suitably qualified and experienced persons.

This set of documents includes a form of certification applicable to Queensland jurisdiction in Addendum A. This is based on similar certification requirements that apply in Queensland to regulated storage structures.

Typically, regulatory authorities use the terms safety and stability, geotechnical specialists who are required to undertake assessments of safety and stability will rely on their training, skills, and experience to do so. The ordering of the terms safety and stability in the guidelines has no special significance other than to conform with typical regulatory usage. While it is unreasonable to expect that predictions of future geotechnical safety and stability can be certified, it is reasonable to expect certification of a process that can provide for sound geotechnical engineering practice, and include informed consideration of potential impacts of the environmental processes that may influence future safety and stability of a post-mining landform.

These guidelines have been developed to provide guidance to geotechnical practitioners regarding a certifiable process for undertaking geotechnical safety and stability assessments for post mining landforms in Australian bituminous and higher rank coal mine settings that have any combination of the following features:

• Excavated highwall, end wall, and footwall slopes;
• Waste rock (spoil) dump slopes, both in-pit and ex-pit;
• Stockpiles;
• Made ground formed by reshaping of formerly excavated slopes or dumped slopes;
• Land surfaces subsided by underground mining excavations.

The guidelines require that geotechnical assessments of subsidence caused by underground mining excavations be undertaken separately from geotechnical assessments of landform safety and stability, but that landform safety and stability assessments may well be informed by findings from subsidence assessments.