Abstract
The evaluation of shear stress versus shear displacement curves is in the main focus of geotechnical engineering. Such curves, depending on the rock assessed, consist of a quasi-linear section, followed by a “kick” representing the peak shear strength, and a residual part, mostly parallel to the abscissa. The aim of the present study is to facilitate the future automatic detection of these crucial characteristics to take a step towards replacing their visual/analogue determination via modern statistical tools. Breakpoint detection methods (Cross-Entropy, Change Point Model) were applied to curves obtained from laboratory shear tests describing the shearing along discontinuities of nine Mont Terri Opalinus Claystone samples. Smooth and moderately rough claystone surfaces were studied. Results indicated that the end of the rising section and the kick observed on the shear strength curves was effectively approximated with the Change Point Model framework. An additional practical advantage of applying statistical tools such as breakpoint detection to shear strength determination is that it ensures the comparability of the obtained results.
Highlights
Shear strength is a crucial parameter in assessing the behavior of soil and rock masses in geotechnical engineering
Besides the properties of the intact soft and well-cemented rocks (Contreras et al 2018; Zhang et al 2018), the properties of the jointed rock and rock discontinuities are very important (Casagrande et al 2018; Renaud et al 2019). One such property is the shear strength along discontinuities, which is a function of the surface roughness, dilatancy and weathering of the rock surface (Barton 2013; Ulusay and Karakul 2016)
In this paper we suggest a statistical toolset not applied before in shear stress versus shear displacement detection, which allows saving significant amount of time and resources and ensures comparability
Summary
Shear strength is a crucial parameter in assessing the behavior of soil and rock masses in geotechnical engineering. Besides the properties of the intact soft and well-cemented rocks (Contreras et al 2018; Zhang et al 2018), the properties of the jointed rock and rock discontinuities are very important (Casagrande et al 2018; Renaud et al 2019) One such property is the shear strength along discontinuities, which is a function of the surface roughness, dilatancy and weathering of the rock surface (Barton 2013; Ulusay and Karakul 2016). It is a fact that samples of different origin characterized by the same joint roughness coefficient can produce very different strengths This implies, that shear stress versus shear displacement curves rarely constitute results that can be approximated with well-defined shear strength envelope curves (Hencher 2015). This creates a challenge for their objective evaluation, due to the fact that, without defining the peak and residual strength it is not possible to draw the envelope curve
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