Estimating uniaxial compressive strength, density and porosity of rocks from the p-wave velocity measurements in-situ and in the laboratory

André Cezar Zingano,João Felipe Coimbra Leite Costa,Rafael Ubirajara Rocha,Paulo Salvadoretti

doi:10.1590/0370-44672021740022

André Cezar Zingano, João Felipe Coimbra Leite Costa + Show 2 more

Open Access

https://doi.org/10.1590/0370-44672021740022

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Abstract

Knowledge of the physical properties of rock masses is fundamental for the economics and safety of mining projects. The determination of these properties in rock samples in the laboratory requires time, expensive equipment and qualified personnel, which considerably increases the information's cost. Indirect methods were developed to obtain properties related to rock masses, which have been shown to be a viable alternative to traditional procedures. The determination of the compressional mechanical wave velocity (Vp) and subsequent correlation with lithological mechanical properties are indirectly obtained. This study’s objective was to obtain correlations between Vp and the resistance to uniaxial compression, UCS (Unconfined Compressive Strength), as well as the density and porosity of the siltstone and sandstone lithologies present in the coalfield of Candiota, located in the southern region of Rio Grande do Sul, Brazil. The Vp records were obtained in laboratory samples, using ultrasonic velocity sensors, and in-situ by geophysical well logging (directly in boreholes). The results indicate the possibility of using Vp to determine the physical parameters of the investigated lithologies. In the specific case of the correlations between Vp and Unconfined Compressive Strength, determination coefficients R2 above 0.70 were obtained, indicating sufficiently high reliability for using this information (e.g. in roof support projects). The correlation between Vp and density was also high.

Highlights

The mechanical and physical properties of rocks are vitally important in the planning of open-pit or underground excavations and analysis of the stability of slopes, caves and other geological structures
This study investigates how uniaxial compressive strength (UCS) versus Vp regressions obtained by sonic logging can be established in carboniferous basins in Brazil, with a coefficient greater than or equal to 0.70, which is considered acceptable from the point of view of international practice
The correlations obtained in this mined by sonic profiling and Pundit) and resistances, porosity, density) of sandstones study involved wave velocities Vp

Summary

Introduction

The mechanical and physical properties of rocks are vitally important in the planning of open-pit or underground excavations and analysis of the stability of slopes, caves and other geological structures. The determination of these properties through the testing of rock samples is a time-consuming and costly activity, which requires accuracy in obtaining, preparing, and testing the samples. There is a need for simple and reliable, indirect techniques to determine the mechanical and physical properties of rocks. Determination of P-wave velocity (Vp) is an applied, non-destructive technique that has increased in its use in geotechnical engineering and can be used to determine geomechanical parameters, either in-situ or in the laboratory. Among the parameters that influence P wave velocity are elastic modulus, density, porosity, shape, anisotropy, presence of water, confining pressure, temperature, and discontinuities

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