Indraratna, B, Oliveira, DAF & Jayanathan, M 2008, 'Revised Shear Strength Model for Soil-Infilled Rock Joints Considering Over-Consolidation Effect', in Y Potvin, J Carter, A Dyskin & R Jeffrey (eds), Proceedings of the First Southern Hemisphere International Rock Mechanics Symposium
, Australian Centre for Geomechanics, Perth, pp. 523-532.
An infilled rock joint is likely to be the weakest plane in a rock mass. The most pronounced effect of the presence of infill material is to reduce the friction of the discontinuity boundaries (i.e. rock to rock contact of the joint walls). The thicker the infill the smaller the shear strength of the rock joint and, once the infill reaches a critical thickness, the infill material governs the overall shear strength and joint walls (rock) play no significant role. However, some infilled joints may gain strength over time due to consolidation mechanisms, but may be weakened upon subsequent joint movements. Several models have been proposed to predict the peak shear strength of infilled joints under both constant normal load (CNL) and constant normal stiffness (CNS) conditions, taking into account the ratio of infill thickness (t) to the height of the joint wall asperity (a), i.e. t/a ratio. CNS models provide a much better accuracy of the infilled joint behaviour in the field but none of these models have focused on the over-consolidation effect of the infilling material. This paper presents a critical review on the existing models and a series of laboratory investigations carried out on idealised saw-toothed rock joints at the University of Wollongong in order to verify the effect of over-consolidation. The tests show how the over-consolidation ratio (OCR) influences the shear strength. The critical thickness, i.e., t/acrit, decreases with increasing OCR. A revised model for predicting the peak shear strength of rough infilled joints considering the effect of OCR is presented on the basis of the laboratory tests performed.
Barton, N. (1974) Review of shear strength of filled discontinuities in rock. Publication No. 105. Oslo: Norwegian Geotechnical Institute, 38 p.
de Toledo, P.E.C. and de Freitas, M.H. (1993) Laboratory testing and parameters controlling the shear strength of filled rock joints. Géotechnique 43, No. 1, pp. 1–19.
Indraratna, B. and Jayanathan, M. (2005) Measurement of pore water pressure of clay-filled rock joints during triaxial shearing. Géotechnique 55, No. 10, pp. 759–764.
Indraratna, B., Welideniya, H.S. and Brown, E.T. (2005) A shear strength model for idealised infilled joints under Constant Normal Stiffness (CNS). Géotechnique 55, No. 3, pp. 215–226.
Indraratna, B., Haque, A. and Aziz, N. (1999) Shear behaviour of idealised infilled joints under constant normal stiffness. Géotechnique 49, No. 3, pp. 331–355.
Indraratna, B. (1990) Development and applications of a synthetic material to simulate soft sedimentary rocks. Géotechnique 40, No. 2, pp. 189–200.
Indraratna, B., Jayanathan, M. and Brown, E.T. (2008) Shear strength model for over-consolidated clay-infilled idealised rock joints. Géotechnique 58, No. 1, pp. 55–65.
Ladanyi, B. and Archambault, G. (1977) Shear strength and deformability of filled indented joints. Proc. 1st Int. Symp. on Geotechnics of Structurally Complex Formations, Capri, pp. 317–326.
Ladd, C.C. and Foott, R. (1974) New design procedure for stability of soft clays. J. Geotech. Engrg., ASCE 100, No. GT7, pp. 763–786.
Papaliangas, T., Lumsden, A.C., Hencher, S.R. and Manolopoulou, S. (1990) Shear strength of modelled filled rock joints. Proceedings Int. Conf. on Rock Joints, N.R. Barton and O. Stephansson (eds.), Balkema (Rotterdam), pp. 275–282.
Patton, F.D. (1966). Multiple modes of shear failure in rocks. Proc. 1st Congr. Int. Soc. Rock Mech., Lisbon, pp. 509–513.
Phien-Wej, N., Shrestha, U.B. and Rantucci, G. (1990) Effect of infill thickness on shear behaviour of rock joints. Rock Joints, Proceedings Int. Conf. on Rock Joints, Loen, N.R. Barton and O. Stephansson (eds.), Balkema (Rotterdam), pp. 289–294.