The effects of rock joint characteristics and normal stress level on the stiffness of rock joints
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ORIGINAL PAPER
The effects of rock joint characteristics and normal stress level on the stiffness of rock joints Milad Abolfazli 1,2
&
Ahmad Fahimifar 2
Received: 15 October 2019 / Accepted: 2 September 2020 # Saudi Society for Geosciences 2020
Abstract The present research aims to study the effects of normal stress level on the rock joint stiffness. In addition, the sample size effect was also taken into consideration. A total of 96 direct shear tests on samples with various sizes and different rock materials were conducted and extensively analyzed. Obtained results show as the normal stress applied increases and shear stiffness (Ks) and normal stiffness (Kn) of the joint increase. Travertine and granite have a similar dilative behavior at lower normal stress levels (lower than 1 MPa). However, when normal stress increases (4 MPa and higher), granite tends to retain its dilative behavior yet roughness in travertine has a significant impact on the joint behavior. An empirical natural logarithmic expression was proposed to describe the stiffness ratio of a rock joint. It was also understood that there is a correlation between the parameters of the logarithmic expression and the roughness of the joints. The empirical expression used to predict the stiffness ratio curves of different joint shows high conformity with the experimental results. Keywords Rock joint . Normal stress . Joint stiffness . Direct shear test . Stiffness ratio
Abbreviations τ Joint shear strength σn Normal stress JRC Joint roughness coefficient JCS Joint compressive strength ϕb Basic friction angle ϕb Basic friction angle Vmax Maximum shear load CNL Constant normal load
Responsible Editor: Zeynal Abiddin Erguler * Milad Abolfazli [email protected]; [email protected] Ahmad Fahimifar [email protected] 1
Department of Civil and Construction Engineering, Swinburne University of Technology, Melbourne, Australia
2
Department of Civil and Environmental Engineering, Amirkabir University of Technology, Tehran, Iran
Introduction Joints which exist in rock masses have always been the center of attention for rock engineers who wish to either design or analyze geotechnical structures such as tunnels and rock slopes (Goodman 1989; Indraratna et al. 1998). Numerous direct shear tests have been carried out by several scientists to investigate the effects of various normal stress levels on the mechanical properties of rock joints. Brown (1970), MüllerSalzburg et al. (1973), Jaeger (1969), Barton (1972), Bandis et al. (1983), and Bandis et al. (1981) tested both natural and artificially made joints to study the strength of rock joints. However, previous research for establishing a comprehensive relationship between deformability characteristics of rock mass and those of a single joint has not been enough (Yoshinaka and Yamabe 1986). Deformability of a rock mass is comprised of the summation of deformations occurred in single joints in addition to those of the intact rock blocks surrounded by the joints. Therefore, determining the deformabilit
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