Authors: Stöckel, B-M; Mäkitaavola, K; Sjöberg, J

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Stöckel, B-M, Mäkitaavola, K & Sjöberg, J 2013, 'Hangingwall and footwall slope stability issues in sublevel caving', in PM Dight (ed.), Slope Stability 2013: Proceedings of the 2013 International Symposium on Slope Stability in Open Pit Mining and Civil Engineering, Australian Centre for Geomechanics, Perth, pp. 1045-1060,

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Mining using large scale underground sublevel caving results in caving of the surrounding host rock and mining-induced ground surface deformations. These effects are most prominent on the hangingwall side, but also develop to some extent on the footwall side of an orebody mined with caving methods. This situation is, in many respects, similar to that of large scale slopes, albeit with the addition of the caved rock. The problem issues are particularly similar for the case when underground mining commences below an existing open pit. The Luossavaara-Kirunavaara AB (LKAB) Kiruna Mine is a case in point, in which underground sublevel caving commenced in the 1960s, following open pit mining that had been on-going since the late 19th century. The mine is in close proximity to the city of Kiruna, which has resulted in a continuous urban transformation of the Kiruna municipality for almost a century. The LKAB industrial area is also strongly affected. With deepened mining, the effects on the ground surface are becoming larger and the demands on monitoring and prediction are larger than ever today. This paper presents a status report concerning large scale slope stability in cave mining and the effects on the surroundings, including currently on-going rock mechanical activities within this subject area. Ground deformations are currently being monitored using Global Positioning System (GPS) techniques on fixed measurement hubs, with measurements taken quarterly of strategically important hubs and annually on all installed hubs (today around 450). LKAB has an on-going research and development project on the use of radar remote sensing (InSAR techniques) for ground deformation monitoring. The advantages of the InSAR techniques are that: (i) measurements have high spatial density, (ii) monitoring occurs more frequently with reduced manpower (currently every 24th day with the Radarsat-2 satellite), and (iii) the need of fixed measurement hubs is eliminated. The theoretical precision is very high but there are issues regarding measurements at high latitudes (snow-covered ground, etc.), which are currently being investigated. The paper also describes the methodology used for predicting ground surface deformations due to mining. Prognoses are produced for planning purposes – both for internal (within LKAB) and external (the municipality of Kiruna, etc.) use. The prognosis methodology employed is based on a combination of analysis of measurement data, numerical modelling, and empirical relations. The resulting prognoses are reviewed annually and updated as required. With the anticipated increase in affected surface area, the precision in prediction needs improvement and LKAB is sponsoring a number of research projects concerning both hangingwall and footwall stability, which are briefly described in the paper.

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