Strata Movement Study Using a 250 m Deep Inclinometer Borehole, Huntly East Coalmine, New Zealand
Du, Z. (2012). Strata Movement Study Using a 250 m Deep Inclinometer Borehole, Huntly East Coalmine, New Zealand (Thesis, Master of Science (MSc)). University of Waikato, Hamilton, New Zealand. Retrieved from https://hdl.handle.net/10289/8740
Permanent Research Commons link: https://hdl.handle.net/10289/8740
Strata movement has adverse impacts on structures located on the surface and in the subsurface within a subsidence basin or affected area. Damages to a mine shaft may result from lateral movement and/ or vertical subsidence of the strata at a depth when the resultant stress is larger than the strength of the lining. My study was developed in collaboration with Solid Energy NZ Limited. My research concentrated on monitoring a 250 m deep borehole to assess changes of strata movement that occurred as underground mining approached the inclinometer borehole. The borehole was a simulation of a proposed shaft. The objectives of my research were to study strata movement characteristics above and adjacent to the North 5 coal mining area by monitoring the inclinometer and interpreting the reading data collected from the inclinometer borehole as the underground mining advanced; develop a model of subsidence using Phase2 software; then compare the modelling subsidence with what we have measured to identify any correlation or difference. The inclinometer borehole was located west of Te Ohaki Road, 300 m from the location of a proposed shaft in the adjacent panel in the Huntly East Mine. A total of 13 sets of inclinometer measurements were undertaken over two years from March 2009. Measurement stopped on 11 March 2011 because the probe could not be lowered through a depth of approximately 38 m in the borehole. My study uses ‘extraction vector’, and ‘movement trajectory of the borehole’ for analysing and interpreting the deep borehole movement in underground mining, and addresses the far field subsidence movement as to its potential impact on structures on the surface or in the subsurface. This thesis also introduces the concept of negative vertical additional friction, developed in China, which is a potentially helpful concept for this study, and the proposed shaft project. Three major movement zones were identified, two ‘shear zones’ from 135.0 to 135.5 m and from 166 to 170 m, and one ‘creeping zone’ from the surface to 115 m. The borehole movement was presented by the trajectory of the intersection of the borehole at depths of surface (1 m), 135 m, and 166 m. The two shear zones occurred on the bedding planes in Te Kuiti Group, the creeping zone occurred in the weak strata of the Tauranga Group and upper Te Kuiti Group. The borehole movements were non-linear, and the borehole lateral movement trajectories varied with depth. Three polynomial equations were developed from regression and modelling for indicating the relationship and predication between the nearest extraction distance and the induced lateral movement. The installation of an inclinometer borehole deeper than 120 m was not found in around 100 literature articles reviewed. No reports of use of inclinometer monitoring of ground movement induced by underground extraction were found in the literature reviewed. According to ASTM (2005), no standards are available yet for evaluation against precision and bias issues arising from use of borehole inclinometer. Therefore, the inclinometer borehole in this study may be one of the most complicated cases for monitoring and measurement of strata movement induced by the underground extraction in New Zealand.
University of Waikato
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- Masters Degree Theses