Shear strength model for overconsolidated clay-infilled idealised rock joints

Abstract

Saturated infilled joints can contribute to the instability of rock masses during undrained shearing. This paper reports an experimental investigation into the effect of the overconsolidation of infilled rough joints on undrained shear behaviour. A revised model is presented for predicting the shear strength of rough infilled joints on the basis of experimental tests carried out on idealised sawtoothed joints with natural silty clay as the infill material. Tests were conducted under consolidated undrained conditions in a high-pressure triaxial apparatus on joints having a dip angle of 608. Pore pressure development in the infill materials was monitored. The results show that the effect of asperities on shear strength is significant up to a critical asperity height to infill thickness ratio (t/a), whereas the shear behaviour is controlled by the infill alone beyond this critical value. The proposed model for predicting the shear strength of rough infilled joints describes how the OCR influences the shear strength, pore water pressure development, and critical t/a ratio.

Numerical Analysis Method of Shear Properties of Infilled Joints under Constant Normal Stiffness Condition

“…ese soft fillings significantly weaken the shear strength of jointed rock and make the rock present more obvious heterogeneity and anisotropy. Infilled joints generally become the weakest position under shear which will easily trigger the whole instability of engineering rock [1][2][3][4]. erefore, the study of shear properties of infilled joints is of significance in both stability evaluation and reinforcement of engineering rock.…”

“…ese influenced factors mainly included material type, surface morphology, initial normal stress, infilled ratio, fillings saturation degree, and overconsolidation degree [1,[5][6][7]. Previous test results showed that soft fillings, such as Green mudstone, serpentinite, and clay, will significantly reduce the shear strength of infilled joints [8], while the high-strength fillings, such as mortar and concrete, enhance the shear strength [6].…”

“…Meanwhile, the in lled ratio, that is, the ratio of lling thickness, t, and the asperity height, a, is a signi cant factor controlling the shear properties of in lled joints. A large number of direct shear test results [1,3,[12][13][14][15][16] showed that the in lled ratio, t/a, has a critical value. If the in lled ratio is less than the critical value, the shear failure strength of in lled joints is typically higher than the shear strength of llings but lower than that of asperity.…”

Laboratory Study of the Shear Behaviour of Natural Rough Rock Joints Infilled by Different Soils

“…During the past 30 years much more information has become available on the shear behavior of joints infilled with soil material. Several models have been proposed to predict the shear strength of infilled joints under both constant normal load (CNL) and constant normal stiffness (CNS) boundary conditions, considering the ratio of infill thickness (t) to the height of the joint wall asperity (a), i.e., t/a ratio [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]. The experimental researches to date have tended to focus on modelled joints or replicas rather than natural rock joints.…”

Dynamic modelling of a mining-induced fault slip

“…In contrast, when the infilling material is sufficiently thick, the shear strength is defined only by the friction angle of the infilling material. Equation 2-16 was further modified so as to take into consideration an influence of consolidation of infilling materials by Indraratna, Jayanathan, and Brown (2008). The revised equation is given as:…”