Pipatpongsa, T, Khosravi, MH, Takemura, J, Leelasukseree, C & Doncommul, P 2016, 'Modelling concepts of passive arch action in undercut slopes', in PM Dight (ed.), APSSIM 2016: Proceedings of the First Asia Pacific Slope Stability in Mining Conference
, Australian Centre for Geomechanics, Perth, pp. 507-520, https://doi.org/10.36487/ACG_rep/1604_33_Pipatpongsa
The classical textbook “Rock Slope Engineering” by Hoek and Bray (1977, p. 166) states that, “It is not usual for the toe of a slope to be undercut ...”. Therefore, it is of great importance to evaluate the maximum undercut width. This is because undercutting at the toe of a slope is considered as a destabilising mechanism. For a problem limiting an undercut slope lying on a bedding plane, a practical technique for surface mining was established at the Mae Moh mine located in Northern Thailand under collaborative research with the Electricity Generating Authority of Thailand. This research successfully resulted in a fundamental study on the failure mechanism of undercut slopes (Pipatpongsa et al. 2009–2013; Khosravi et al. 2009–2012, 2016). The possible modes of slope failure, due to an excavation at the toe of a slope, were examined through a series of simple physical model tests using humid sand placed on an inclined rigid plate. While ensuring the removal of propped portions of sand at the toe of the slope did not cause the collapse of the sand mass, due to arch action over the abutments. However, the effect of the arch action could not be maintained once the excessive removal of propped portions had been made. Different failure modes were observed in accordance with various boundary/material conditions. The arch action and its mechanism of load transfer were confirmed through a number of physical and numerical models. The failure mechanism along the inclined plane of weakness was seen to involve the passive condition, whereby the major principal stresses dominate the force supporting the arches in the circumferential direction, and the minor principal stresses represent the force confining the stacks of arches. This paper summarises the concepts used in setting up 1 g physical models, the required equipment and the measurement techniques. The development of the physical models in the preliminary study, the 1 g physical modelling and the geotechnical centrifuge modelling conducted from 2010–2015 are also reviewed. Based on the results of field tests, the new design concept for undercut slopes proposed in the previous study (Pipatpongsa et al. 2013) is correctly revised in this paper.
Keywords: undercut slope, physical modelling, arching effect, excavation, coal mining
Bosscher, PJ & Gray, DH 1986, ‘Soil arching in sandy slopes’, Journal of Geotechnical Engineering-ASCE, vol. 112, no. 6, pp. 626–645.
EGAT (Electricity Generating Authority of Thailand) 1985, Thailand-Australia Lignite Mines Development Project, Geotechnical Report, Mae Moh Mine, vol. 3.
Guo, P & Zhou, S 2013, ‘Arch in granular materials as a free surface problem’, International Journal for Numerical and Analytical Methods in Geomechanics, vol. 37, no. 9, pp. 1048–1065.
Hoek, E & Bray, J 1977, Rock Slope Engineering, The Institution of Mining and Metallurgy, London.
Hong, WP, Lee, JH & Lee, KW 2007, ‘Load transfer by soil arching in pile-supported embankments’, Soils and Foundations, vol. 47, no. 5, pp. 833–843.
Jenike, AW 1961, ‘Gravity flow of bulk solid’, Bulletin of the Utah Engineering Experiment Station, vol. 52, no. 29, pp. 1–309.
Khosravi, MH 2012, ‘Arching effect in geomaterials with applications to retaining walls and undercut slopes’, Doctoral thesis, Tokyo Institute of Technology.
Khosravi, MH, Pipatpongsa, T, Leelasukseree, C & Wattanachai, P 2009, ‘Failure mechanisms in arched excavation of sloped earth using model test’, in Proceedings of Geo-Kanto 2009, Japanese Geotechnical Society, Tochigi, pp. 241–246.
Khosravi, MH, Carlton, OJ, Pipatpongsa, T, Takemura, J & Doncommul, P 2010, ‘A preliminary study of moving-pit excavation for environmental load reduction in open-cast mining’, in Proceedings UP ICE Centennial Conference on Harmonizing Infrastructure with the Environment featuring the 3rd ASEAN Civil Engineering Conference and the 3rd ASEAN Environmental Engineering Conference, University of the Philippines Diliman, p. GEO_11.
Khosravi, MH, Pipatpongsa, T, Takahashi, A & Takemura, J 2011a, ‘Arch action over an excavated pit in a stable scarp investigated by physical model tests’, Soils and Foundations, vol. 51(4), pp. 723–735.
Khosravi, MH, Pipatpongsa, T, Takemura, J, Mavong, N & Doncommul, P 2011b, ‘Investigation on shear strength of shale at the Mae Moh open-pit mine’, in Proceedings of the 4th Thailand-Japan International Academic Conference, Thai Students' Association in Japan under the Royal Patronage, The University of Tokyo, pp. 51–52.
Khosravi, MH, Tang, L, Pipatpongsa, T, Takemura, J & Doncommul, P 2012, ‘Performance of counterweight balance on stability of undercut slope evaluated by physical modeling’, International Journal of Geotechnical Engineering, vol. 6(2), pp. 193–205.
Khosravi, MH, Pipatpongsa, T & Takemura, J 2013, ‘Interface shearing resistance properties between moist silica sand and surface of materials investigated by direct shear apparatus’, Geo-Kanto2013, Japanese Geotechnical Society, Miraikan, Tokyo, pp. MAT 4–5.
Khosravi, M, Takemura, J, Pipatpongsa, T & Amini, M 2016, ‘In-flight excavation of slopes with potential failure planes’, Journal of Geotechnical and Geoenvironmental Engineering, vol. 142, no. 5, pp. 06016001.
Lambe, TW & Whitman, RV 1969, Soil Mechanics, John Wiley & Sons, Inc.
Leelasukseree, C, Pipatpongsa, T, Khosravi, MH & Mavong, N 2012, ‘Stresses and a failure mode from physical and numerical models of undercut slope lying on inclined bedding plane’, in Proceedings of 7th Asian Rock Mechanics Symposium, Seoul, pp. 1295–1304.
Low, BK, Tang, SK & Choa, V 1994, ‘Arching in piled embankments’, Journal of Geotechnical Engineering, vol. 120(11), pp. 1917–1938.
Pipatpongsa, T, Heng, S, Likitlersuang, S, Mungpayabal, N & Ohta, H 2011, ‘Investigation of mechanical properties of clay seam in bedding shears of the Mae Moh open-pit mine of Thailand’, in M Shahin & H Nikraz (eds), Proceedings of the International Conference on Advances in Geotechnical Engineering, Perth, pp. 209–214.
Pipatpongsa, T, Khosravi, MH, Doncommul, P & Mavong, N 2009, ‘Excavation problems in Mae Moh lignite open-pit mine of Thailand’, in Proceedings of Geo-Kanto 2009, Tochigi, pp. 459–464.
Pipatpongsa, T, Khosravi, MH, Leelasukseree, C, Mavong, N & Takemura, J 2010, ‘Slope failures along oblique plane due to sequential removals of propping portion in physical model tests’, in 15th National Convention on Civil Engineering, Engineering Institute of Thailand, Ubon Ratchathani University, vol. GTE60, p. 135.
Pipatpongsa, T, Khosravi, MH, Takemura, J, Stathas, D & Leelasukseree, C 2012, ‘Cohesive arch action in laterally confined block of moist sand placing on an inclined bedding plane’, in Proceedings of 7th Asian Rock Mechanics Symposium, Korean Society for Rock Mechanics, Seoul, pp. 1378–1387.
Pipatpongsa, T, Khosravi, MH & Takemura, J 2013, ‘Physical modeling of arch action in undercut slopes with actual engineering practice to Mae Moh open-pit mine of Thailand’, in 18th International Conference on Soil Mechanics and Geotechnical Engineering, The French Society for Soil Mechanics and Geotechnical Engineering, Paris, vol. 2, pp. 943–946.
Terzaghi, K 1936, ‘Stress distribution in dry and in saturated sand above a yielding trap-door’, in First International Conference on Soil Mechanics and Foundation Engineering, Harvard University, Cambridge, vol. 1, pp. 307–311.
Tsai, JS & Chang, JC 1996, ‘Three-dimensional stability analysis for slurry-filled trench wall in cohesionless soil’, Canadian Geotechnical Journal, vol. 33, no. 5, pp. 798–808.
Walker, DM 1966, ‘An approximate theory for pressures and arching in hoppers’, Chemical Engineering Science, vol. 21, no. 11, pp. 975–997.
Wang, WL & Yen, BC 1974, ‘Soil arching in slopes’, Journal of the Geotechnical Engineering Division - ASCE, vol. 100, no. GT1, pp. 61–78.
White, DJ, Take, WA & Bolton, MD 2003, ‘Soil deformation measurement using particle image velocimetry (PIV) and photogrammetry’, Geotechnique, vol. 53, no. 7, pp. 619–631.
Wong, GCY 1984, ‘Stability analysis of slurry trenches’, Journal of Geotechnical Engineering, vol. 110, no. 11, pp. 1577–1590.
Wong, RCK & Kaiser, PK 1991, ‘Performance assessment of tunnels in cohesionless soils’, Journal of Geotechnical Engineering-ASCE, vol. 117, no. 12, pp. 1880–1901.
Wyllie, DC & Mah, C 2004, Rock Slope Engineering, CRC Press. ADDIN EN.REFLIST