Prediction of Peak Shear Strength of Natural, Unfilled Rock Joints Accounting for Matedness Based on Measured Aperture

Francisco Ríos-Bayona,Diego Mas-Ivars,Fredrik Johansson

doi:10.1007/s00603-020-02340-8

Francisco Ríos-Bayona, Diego Mas-Ivars + Show 1 more

Open Access

https://doi.org/10.1007/s00603-020-02340-8

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Abstract

The mechanical behaviour of natural, unfilled rock joints is influenced by the interaction between surface roughness and matedness of the contact surfaces. In the field, natural rock joints normally exhibit a mismatch between the contact surfaces, mainly due to different geological processes such as weathering or deformations. Various attempts have been made to estimate how matedness of rock joints influences their peak shear strength. However, the proposed methodologies imply certain difficulties since they are intended to estimate the matedness of rock joints based mainly on visual inspection, and by relating an initial shear displacement to the length of the analysed sample or by relating the opening of saw-tooth and two-dimensional joint profiles with the degree of interlocking. Therefore, a tested peak shear strength criterion for natural, unfilled rock joints that realistically accounts for the influence of matedness on their peak shear strength is still lacking. This paper presents a methodology where objective measurements of the average aperture of natural, unfilled rock joints are used to estimate their matedness as a step in the prediction of the peak shear strength. This measured average aperture is based on high-resolution optical scanning of the surface roughness. The proposed relationship between measured average aperture and matedness of natural rock joints has been included in a further developed peak shear strength criterion. The verification against ten natural rock joint samples of coarse-grained granite showed that the revised criterion can predict the peak shear strength considering rock joint matedness.

Highlights

The assessment of rock joint shear strength is one of the most common problems that engineers face in the design and construction of engineering structures on or in rock masses
In this paper we present a revised peak shear strength criterion with the ability to account for both the threedimensional characteristics of the surface roughness and the matedness of natural, unfilled rock joints
Based on the performed analysis and experiments in the laboratory, it can be concluded that the revised peak shear strength criterion is able to predict the peak shear strength of natural, unfilled rock joints under the conditions tested in this study

Summary

Introduction

The assessment of rock joint shear strength is one of the most common problems that engineers face in the design and construction of engineering structures on or in rock masses (e.g., stability analysis of dams, block and arching stability in tunnels, slope stability analysis). It is widely recognised that the peak shear strength of rock joints is affected by a number of different parameters, for example the normal stress acting on the joint surface, the degree of weathering, mineral coatings and infillings, surface roughness, the matedness of the rock joint and the scale. Over the past few years, technical developments have shown that surface roughness can be accurately and characterised in three dimensions using high-resolution optical scanning measurements (Lanaro et al 1998; Grasselli 2006) This approach led to new criteria that tried to explain rock joint shear strength behaviour based on three-dimensional quantification of surface roughness (Grasselli and Egger 2003; Yang et al 2016; Dong et al 2017; Liu et al 2017). The mechanical behaviour of rock joints has been tackled from a semi-analytical stochastic perspective (Casagrande et al 2018)

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