Abstract
Uniaxial compressive strength (UCS) is the most used parameter to measure rock strength. However, restrictions in sampling large volume of material, the need of very large set of results and onsite characterisation of UCS non-destructively are requirements in many scientific and engineering investigations. The estimation of UCS from a single non-destructive or minimally invasive technique (NDT) may result incomplete because each NDT is sensitive to different compositional and textural factors. This paper combines open porosity, P-wave velocity, Leeb hardness and micro-drilling resistance force to estimate USC for a wide range of carbonate sedimentary rock types with different petrographic characteristics. Results reveal that mineralogical composition significatively affects micro-drilling resistance force profiles and P-wave velocity values, especially for quartz-bearing rocks. In addition, texture controls substantially the reproducibility of tests sensible to rock surface properties, such as Leeb hardness and micro-drilling resistance force. Fifteen simple and multiple expressions for UCS are fitted. Linear expressions have shown better coefficients of determination (R 2 ) than non-linear equations because of the linearity shown by individual parameters. Curve fitting improves as the number of petrophysical parameters increase in the multiple linear regression analysis. The best correlation is found when the equation incorporates all the mechanical parameters obtained non-destructively as well as open porosity (R 2 = 0.910). Leeb hardness is always the most significant variable of the fitted regressions and its addition into multiple linear equations causes an increase of R 2 . Open porosity also improves R 2 whereas drilling force and P-wave velocity have a lower statistical weight in the expressions. The UCS estimation from all NDT, without considering open porosity, shows a good correlation (R 2 = 0.899), which presents the advantage that they can be obtained non-destructively with portable equipment and can provide a numerous set of results at relatively low cost. • Compositional and textural factors affect differently to the mechanical parameters. • Leeb hardness is the most significant variable in the fitted regressions. • The best UCS estimation incorporates all NDT parameters as well as open porosity. • Portability is one of the main advantages of NDTs.
Highlights
Uniaxial compressive strength (UCS) is, arguably, the most relevant parameter in most fields of applied geosciences, engineering and ma terial science, as it establishes the mechanical response of material under unconfined conditions
This paper aims to estimate the uniaxial compressive strength by combining non-destructive or minimally invasive techniques for a wide range of carbonate sedimentary rock types with different petrographic characteristics
We classified the studied rocks based on the following textural properties: (i) rocks were divided into three textural groups depending on the particle size: fine-grained (F), where the mean particle diameter is smaller than 0.5 mm; medium-grained (M) with particle diameter 0.5–2 mm; and coarse-grained (C) for particle diameter larger than 2 mm.[20] (ii) studied rock samples were classified into non-porous or low porous, with porosity values lower than 10%, and porous (P), in which porosity is greater than 10%
Summary
Uniaxial compressive strength (UCS) is, arguably, the most relevant parameter in most fields of applied geosciences, engineering and ma terial science, as it establishes the mechanical response of material under unconfined conditions. Recent investigations on physico-mechanical properties and dura bility of rocks are focusing on the use of onsite and non-destructive or minimally invasive techniques (NDT) for UCS estimation.[1,2,3,4,5,6,7,8] There is a wide range of portable NDTs used for these estimations: the most common and widely tested techniques include the measurement of the ultrasonic wave velocity, surface hardness using impact-based equipment (such as Schmidt hammer or Leeb hardness test) and the Drilling Resistance Measurement System (DRMS) test (so-called micro-drilling). Research on the relationships between these techniques and UCS for a wide variety rock types is an increasingly hot topic.[9,10,11]
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