Abstract The Northern Wedge Failure (NWF) is a complex failure mass within Whitehall Quarry, Cambridge, New Zealand. Initiation of failure of the c. 500 000 m3 mass occurred during spring of 1988. Complete failure was expected following displacement recordings of 2.3–5.6 m a−1; however, this did not eventuate. By the mid 1990s, the failure mass was deemed stable. In 2010, an engineering geological investigation was conducted to assess the stability of the NWF at that time. The rock mass that failed comprises moderately dipping interbedded feldspathic sandstone and argillaceous mudstone below a thin alluvial cover. It is bound by two fault planes, both exhibiting up to 100 mm of gravelly clay fault gouge. X-ray diffraction analysis of the gouge indicated the presence of kaolinite and montmorillonite, and Atterberg Limit tests showed the plastic and liquid limits to be 31% and 51%, respectively. Electronic distance monitoring (EDM) was carried out over 12 months. Recorded velocities increased by 17% above the 21 mm/month baseline over the wetter months. Limit equilibrium analysis carried out using historic and recent field and laboratory observations input to the computer software SWedge estimated a Factor of Safety (FOS) of 0.97. Complete failure of the NWF could be initiated at any time by an extended period of heavy rainfall and/or unloading of the toe or the stripping of overburden.
北楔破坏(NWF)是位于新西兰剑桥怀特霍尔采石场的一个复杂破坏体。大约50万立方米的质量在1988年春天开始破坏。在2.3-5.6 m a−1的位移记录下，预计完全失效;然而，这并没有发生。到20世纪90年代中期，破坏团被认为是稳定的。2010年进行了工程地质调查，对当时的NWF稳定性进行了评估。破坏的岩体包括薄冲积盖层下的中等倾斜互层长石砂岩和泥质泥岩。它被两个断层面所束缚，两个断层面都显示出高达100毫米的含砾粘土断层泥。x射线衍射分析表明泥中含有高岭石和蒙脱石，Atterberg极限测试显示泥的塑性限为31%，液限为51%。电子远程监测(EDM)进行了超过12个月。在较潮湿的月份，录得的流速较21毫米/月的基线上升了17%。极限平衡分析使用历史和最近的现场和实验室观测输入到计算机软件SWedge，估计安全系数(FOS)为0.97。由于长时间的强降雨和/或趾部卸载或覆盖层剥落，NWF随时可能完全失效。
{"title":"Whitehall quarry, Northern Wedge failure: 22 years of investigation","authors":"D. R. Strang","doi":"10.1144/EGSP27.10","DOIUrl":"https://doi.org/10.1144/EGSP27.10","url":null,"abstract":"Abstract The Northern Wedge Failure (NWF) is a complex failure mass within Whitehall Quarry, Cambridge, New Zealand. Initiation of failure of the c. 500 000 m3 mass occurred during spring of 1988. Complete failure was expected following displacement recordings of 2.3–5.6 m a−1; however, this did not eventuate. By the mid 1990s, the failure mass was deemed stable. In 2010, an engineering geological investigation was conducted to assess the stability of the NWF at that time. The rock mass that failed comprises moderately dipping interbedded feldspathic sandstone and argillaceous mudstone below a thin alluvial cover. It is bound by two fault planes, both exhibiting up to 100 mm of gravelly clay fault gouge. X-ray diffraction analysis of the gouge indicated the presence of kaolinite and montmorillonite, and Atterberg Limit tests showed the plastic and liquid limits to be 31% and 51%, respectively. Electronic distance monitoring (EDM) was carried out over 12 months. Recorded velocities increased by 17% above the 21 mm/month baseline over the wetter months. Limit equilibrium analysis carried out using historic and recent field and laboratory observations input to the computer software SWedge estimated a Factor of Safety (FOS) of 0.97. Complete failure of the NWF could be initiated at any time by an extended period of heavy rainfall and/or unloading of the toe or the stripping of overburden.","PeriodicalId":266864,"journal":{"name":"Engineering Geology Special Publication","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125992301","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract Surface mining of coal can involve extensive footwall slopes parallel to shallow to moderately dipping coal measures strata. Footwall failure mechanisms typically invoke bedding-parallel defects but also require either the existence of flatter structures, which cross-cut bedding, or require break-out through the rock mass to allow failure surfaces to emerge. Permian-aged Baralaba Coal Measures of the Bowen Basin, Queensland, are prospective for coal with extraction by open-pit methods. The Baralaba Coal Measures contains multiple seams within an interburden sequence comprising sandstone, siltstone, mudstone and carbonaceous variations. The coal measures sequence has been deformed into a complex pattern of NW-striking folds which has resulted in bedding dip ranging from 15° to 60°. Bedding has been classified as shallow (10–30°) to moderate (30–60°). Geotechnical investigations conducted to support coal extraction up to depths of 200 m suggest that structural controls strongly influence footwall slope design. For the purpose of footwall slope design, a distinction can be made between deposit areas of relatively simple structure (uniformly dipping bedding on fold limbs) and structurally complex areas (where layer-parallel shortening close to fold hinges has resulted in a system of low-angle thrusts and asymmetrical minor folds).
{"title":"Geological structural controls on stability of footwall slopes: an example from the Bowen Basin, Queensland","authors":"D. Pope, A. Duran, G. Grocott, O. Holm, A. Bell","doi":"10.1144/EGSP27.9","DOIUrl":"https://doi.org/10.1144/EGSP27.9","url":null,"abstract":"Abstract Surface mining of coal can involve extensive footwall slopes parallel to shallow to moderately dipping coal measures strata. Footwall failure mechanisms typically invoke bedding-parallel defects but also require either the existence of flatter structures, which cross-cut bedding, or require break-out through the rock mass to allow failure surfaces to emerge. Permian-aged Baralaba Coal Measures of the Bowen Basin, Queensland, are prospective for coal with extraction by open-pit methods. The Baralaba Coal Measures contains multiple seams within an interburden sequence comprising sandstone, siltstone, mudstone and carbonaceous variations. The coal measures sequence has been deformed into a complex pattern of NW-striking folds which has resulted in bedding dip ranging from 15° to 60°. Bedding has been classified as shallow (10–30°) to moderate (30–60°). Geotechnical investigations conducted to support coal extraction up to depths of 200 m suggest that structural controls strongly influence footwall slope design. For the purpose of footwall slope design, a distinction can be made between deposit areas of relatively simple structure (uniformly dipping bedding on fold limbs) and structurally complex areas (where layer-parallel shortening close to fold hinges has resulted in a system of low-angle thrusts and asymmetrical minor folds).","PeriodicalId":266864,"journal":{"name":"Engineering Geology Special Publication","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132844453","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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