Authors: Mercer, KG

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Mercer, KG 2013, 'Ongoing research into anisotropic rock masses using numerical modelling', 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. 237-247,

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This paper details results from the ongoing numerical modelling research into the shear strength characteristics of planar anisotropic rock masses such as those found in the Pilbara region of Western Australia. Numerical simulations using the distinct element code UDEC were used to model different weathered anisotropic rock formations such as shales and Banded Ironstone Formations (BIFs). These simulations confirmed the overall shear strength reduction due to sliding on planar discontinuities at angles sub-parallel to bedding and better quantified the difference between the planar anisotropic transition models (ATMs) for shale and BIF. However, the modelling revealed a zone of upslope shear strength reduction (USSR) which can occur at positive angles of anisotropy (AoA) between 40 to 90° under certain rock mass configurations. This zone was identified but not previously quantified in earlier studies. The magnitude of the shear strength reduction is dependent on the tensile strength of the intact rock as well as bedding parting spacings. The USSR has significant implications especially in relation to the effect on the stability of slopes having particular configurations of anisotropic rocks. The current ALM1 and ALM2 do not take the USSR into account and therefore can potentially overestimates the shear strength of the rock mass in this range of AoA. Consequently a new ALM (ALM3) has been developed which does take the USSR into account. Until the ALM3 is coded into commercial software and the new ALM3 parameters more rigorously defined, care should be exercised when assessing the stability of slopes having these geological formations and geometry.

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