Landslides and erosion pose significant hazards to mining and engineering activity in the remote mountainous terrain of Western Province, Papua New Guinea. The investigation and containment of these hazards have been the concern of the Ok Tedi open-cast copper mine since engineering feasibility studies began in 1978. Subsequent terrain hazard mapping has identified numerous landslides and rock avalanche deposits in the Ok Tedi catchment and in the immediate vicinity of the mine, ranging from very low frequency, catastrophic rock avalanches through to mudslides and mudflows that recur on a daily or weekly basis. This mapping formed part of a multidisciplinary geotechnical study instigated by Ok Tedi Mining Limited and comprised detailed slope inventory, geomorphological mapping combined with air photograph interpretation and a review of pre-existing structural geological and geotechnical data. The study area was sub-divided into 245 zones and assigned hazard and risk categories or levels derived from the field data. These classifications were presented in map form at 1:10 000 scale along with prioritized recommendations for further investigation, monitoring and remedial action, where appropriate.
The Sakhalin Energy Investment Company Ltd (SEIC) Sakhalin II Phase 2 oil and gas pipeline corridor is 782 km in length, and extends from landfall sites in the north of the island to a liquefied natural gas plant and oil export terminal in the south. For c . 120 km this alignment crosses the Makarov Mountains, an approximately north–south-orientated grouping of ridges and valleys formed in Cretaceous mudstones, Tertiary siltstones, sandstones, coal measures, lavas and tuffs. Situated on the NW Pacific rim, the island is prone to seismic activity, and the design and construction of the pipelines’ alignment has had to take into consideration a number of existing landslides (more than 400 in total). Additionally, the continuing seismic hazard, combined with slope toe erosion by rivers and high groundwater tables brought about by spring snow melt and summer rains, creates a potential for first-time landslides to occur during the 50 year operational period of the pipelines. To assess where such failures might take place a study was undertaken that combined back-analysis and sensitivity analysis, landslide susceptibility analysis (including factor analysis) and qualitative evaluation. The qualitative evaluation allowed a judgement-based assessment to be included in the identification and prioritization of potential future first-time failure areas. Ground truthing was then undertaken in the areas of highest susceptibility, and generally supported the findings of the analysis. In c . 50% of these cases the potential for landslide initiation was considered to be sufficiently high to warrant intervention, in terms of ground investigation, slope movement and groundwater monitoring, or engineering mitigation. The study highlights the uncertainties that exist when undertaking exercises such as these where geotechnical information is insufficient to carry out rigorous modelling and where broad geological and geographical assessments have to be made in order to yield the required outputs.
The high-altitude desert landscape of Ladakh poses a number of obstacles and challenges to sustainable engineering, the development of natural resources, livelihood improvement and the protection of communities and infrastructure from natural hazards. Severe terrain, extremes of climate, floods, landslides and erosion are major factors to contend with and lessons can be learnt from the history of engineering management in the region. Geological and geohazard studies must be integral components of future development plans, combining remote sensing with field investigations. Engagement with local communities will provide valuable historical context concerning the behaviour of the landscape and will help define the land management approaches best suited to engineering intervention.
The approach to ground modelling should be devised to suit the geological and geomorphological challenges that pertain and the context and manner in which the model is to be used. Several case studies are examined where problems experienced during works construction and operation are associated with complex ground conditions and geomorphological outcomes not fully anticipated from the site investigation and ground modelling. Other cases reflect situations where either important existing information was ignored or no apparent consideration was given to the potential for ground engineering problems. Insufficient attention to geomorphology, and especially geomorphological processes, has been the cause of several construction difficulties and continues to pose a significant source of risk in many terrains. The observational and analytical skills of a carefully-chosen geo-team will be paramount if these challenges are to be overcome. However, such considerations become largely academic if institutional shortcomings serve to limit or exclude engineering geological assessment in the first place.Thematic collection: This article is part of the Ground models in engineering geology and hydrogeology collection available at: https://www.lyellcollection.org/cc/Ground-models-in-engineering-geology-and-hydrogeology
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