Lithological units have been classified geotechnically with mechanical tests and discontinuity measurements in the Rotowaro coal mine open pits, New Zealand. Using these measurements slope stability probability classifications (SSPC) have been quantified based on an adaption of HackÕs (1998) SSPC system which places less influence on rock quality designation and unconfined compressive strength than previous rock mass rating systems. The Hack weathering susceptibility rating has been modified by using chemical index of alteration values from XRF major element analysis. Another major component of this adapted SSPC system is the inclusion of rock moisture content effects on slope stability. This paper explains the systematic approach of using the adapted SSPC system to classify slope stability probability.


This paper describes a system for quantifying slope stability which is being tested on opencast mines in three coalfields within the Waikato Coal Region. These mines being the Kopako mine in the Maramurua Coalfield, all operating pits in the Rotowaro Coalfield and the disused Pirongia mine in the Kawhia Coalfield. These fields are in the north, central and southern areas of the Waikato Coal Region respectively. This paper details the slope stability probability system using a slope in the Township pit of the Rotowaro Coalfield. The Rotowaro Coalfield, is located within the northern subregion of the Waikato Coal Region, and has been mined by both underground and opencast methods between 1915 and present day. Prior to 1947 the dominant mining technique was by underground methods, but subsequently, as technology and demand increased, opencast mining became the dominant method of winning the coal. Where opencast mining is being undertaken, the engineering geological and geotechnical character of the overburden that is to be removed must be known, so that optimal pit design and management techniques are used.

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