Engineering Geology and Geotechnical Investigation of Highwall Stability of the Proposed Cypress Opencast Mine Mt William Fault Zone, Cypress North Block Upper Waimangaroa

• Main Author: Pehi, Te Ngere Russell
• Format: Other/Unknown Material
• Language: English
• Published: University of Canterbury. Geological Sciences 2004
• Subjects: Greenland
• Online Access: http://hdl.handle.net/10092/3910; https://doi.org/10.26021/9087

The objective of this thesis was to develop a comprehensive understanding of the geotechnical nature of the proposed Cypress North Block Opencast Coalmine highwall in the Mt William Range east of present mine operations at Stockton Opencast. An investigation was undertaken to gather information on the rock material and rock mass properties of the Basement, Brunner Coal Measures, and Kaiata Mudstone stratigraphic units that would make up the composition of the proposed highwall. The specific aims of the thesis were to identify the distribution of rock types and the locations and orientations of mappable defects such as faults, joints, shears, and crush zones. The stratigraphic units are subdivided into their respective geotechnical units based on physical, and mechanical intact rock material parameters. The basement lithologies comprised of interfingered layers of Greenland Group metasediments and intrusive Berlins Porphyry granite/granodiorite. These were divided into 3 geotechnical units where analyses of the rock parameters were determined. These units (Berlins Porphyry, Greenland Group hornfels, & mixed basement) returned mean values of low porosity (n= 0.8-2.3%), and slake durability index results (Id2 =99.0-99.6% retained), and high friction angles (40.6-44.5º), dry densities (2657-2666Kg/m³), and moderate UCS (78.8 -136.6MPa), tensile splitting strength (5.1 - 6.2 MPa), and cohesion values (6.38MPa). The Brunner Coal Measures are an alternating sedimentary sequence of massive sandstones, laminated sandstones, siltstones, mudstones, and coal that were divided into 5 geotechnical units. Due to a lack of samples recovered from the two drillholes (DH 1694 and DH 1717) that penetrated this layer limited results were returned. Testing was constrained to the coarse-medium grained lithology which showed high porosities (n=7.9%), and slake-durability index results (Id2=94.0% retained), and moderate friction angles (33.2º), and dry densities (2411Kg/m³), and low strength characteristics with UCS intact rock ...