Correlations of rock mass classifications applied to ferruginous caves

Paula Leal Oliveira,Hernani Mota De Lima

doi:10.1590/0370-44672019730017

Paula Leal Oliveira, Hernani Mota De Lima

Open Access

https://doi.org/10.1590/0370-44672019730017

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Abstract

Abstract For the Brazilian iron ore mines, the presence of caves presents a challenge, since most of them are located within the ore deposit. The National Environment Commission (CONAMA 347 Resolution/2004) establishes that the speleological heritage, as well as its area of influence, cannot sustain irreversible environmental impacts. The physical integrity of caves adjacent to mining operations is an issue of pivotal importance to be scrutinised in studies towards the delimitation of the cave’s protection radius. This article presents the study of various models of correlation between the RMR and Q systems used for the stability assessment of natural iron ore caves. In order to study a correlation between the RMR and Q systems, the most popular rock mass classifications, and their application as a validation tool, a selection of measurements of Q and RMR, organized in a database from seven natural caves of ferruginous lithology, are submitted to a study and statistical analysis. An empirical equation was obtained from the data, using a simple linear regression. The result of the regression was compared with selected correlation equations and the best fit for the data was chosen. The best fit was the Rutledge & Pearson correlation equation, which presented the best combination of R² and S, after the equation created on basis of the real values for RMR, though the other equations have results similar to it. As the results were quite similar, the recommendation still is that correlations should be used with caution, and associated to other methods and field analysis.

Highlights

Caves are natural openings formed underground, as the speleological definition, wide enough for man's entrance
The stability assessment of a rock mass begins by understanding its behavior and the rock mass classification systems are considered the best tools for this (Barton et al, 1974 and Bieniawski, 1989)
The objective of this study is to identify among the existing correlations, which one fits better for the study of the stability of ferruginous cavities, returning the smallest errors

Summary

Introduction

Caves are natural openings formed underground, as the speleological definition, wide enough for man's entrance. The demand for protection of these structures, imposed by Brazilian legislation, has led to an intensification and deepening of speleological studies, but research concerning caves of ferruginous lithologies is recent. These consisted of 14% of the Brazilian speleological potential (CECAV 2018), only recently did the scientific community consider iron formations as a lithology favorable to the formation of caves. One of the criteria is the geotechnical fragility of the cavities – a factor linked to the stability of the cavities, their genesis and evolution. There is no system developed for application in underground cavities, but classifications can be applied for this purpose, with appropriate adaptations such as Genis e Çolak(2015), Noce (2016), Dutra (2017), Jordá-Bordehore (2017) andPaula et al (2018)

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