QUANTIFICATION OF PARAMETERS FOR ENGINEERING BEHAVIOUR OF JOINTED ROCKS

Abstract

To Study the engineering behaviour of jointed rock masses, it is necessary to have a good understanding of the influence of joints on the strength and deformation response of the jointed mass. Compared to the in-situ tests which are expensive, time consuming and difficult to perform, the model studies conducted in a systematic way on rock specimens in the laboratory can yield valuable results which can be applied to the actual field problems. A number of research workers have studied the strength and the deformational response of jointed rocks on modelled materials, to mention a few, Brown (1970), Einstein and Hirschfeld (1973), Yaji (1984), Baoshua et al., (1986), Arora (1987), Roy (1993), Kulatilake et al., (1997), Singh (1997), Yang et al, (1998). It has been observed that the majority of the above mentioned researchers who have conducted model studies on jointed rock specimens have not attempted to show the combined influence of joint frequency, joint orientation, joint roughness or strength along the joint. and other features of the rock mass to reflect the change in quality of the intact rock, whereas they have considered individually either joint sets or joint orientations. In view of this, researchers like Ramamurthy, et al, (1994), Kulatilake et al., (1994) and Singh and Choudhari, (2007) proposed the "Weakness Coefficient concepts" wherein the strength and deformation modulus of jointed rock mass is found by introducing weakening effects of joints on the intact rock properties. In the present study experimental data has been collected related to model studies on jointed rock specimens conducted by various research workers i.e., Brown and Trollope, (1970a,b), Einstein and Hirschfeld (1973), Baoshua et al.,(1986), Arora (1987), Yaji (1984), Roy (1993) Kulatilake et al.,(1997), Singh (1997), and Yang et al., (1998). By using this data base, the applicability of the weakness coefficient concepts like Joint Factor Concept proposed by Ramamurthy et al., (1994), Fracture Tensor concept proposed by Kulatilake et al., (1994), and Modified Joint Factor concept proposed by Singh and Choudhari (2007) has been studied. Based on the analysis carried out, equations have been proposed relating the strength and deformational properties of the jointed rock model specimens to the Joint factor, Modified Joint Factor and Fracture Tensor coefficients.