Leeb Hardness Test for UCS estimation of Sandstone

Yassir Asiri

In the proceedings of: GeoVancouver 2016: 69th Canadian Geotechnical Conference

Session: FUNDAMENTALS - III Soil & Rock Mechanics

ABSTRACT: type) values (HLD) and unconfined compressive strength values (UCS) for sandstone. Moreover, the Leeb test methodology was evaluated, such as sample size and the number of Leeb readings that comprise a valid test result. The laboratory testing was carried out on sandstone samples and combined with other literature values to develop a database with a total of 45 test results. Statistical analysis was carried out on the database and the results of correlation analysis from tests are presented. A reasonable correlation was found to exist between LHD and UCS for sandstone. The results show that the Leeb Hardness test can be particularly useful for field estimation of UCS. The method is fast, simple and equipment costs are low. The hardness testing cannot replace UCS tests but can complement these tests, especially if data is needed immediately or other testing is not possible.

RÉSUMÉ: Une exploration expérimentale a été menée pour étudier la relation statistique entre Leeb Dureté (type «D») des valeurs (HLD) et des valeurs de résistance à la compression uniaxiale (UCS) pour la roche. En outre, la méthodologie de test Leeb a été évaluée, comme la taille de l'échantillon et le nombre de lectures Leeb qui comprennent un résultat de test valide. Les tests de laboratoire ont été effectuées sur des échantillons de grès et combiné avec d'autres valeurs de la littérature pour développer une base de données avec un total de 45 résultats. L'analyse statistique a été réalisée sur la base de données et les résultats de l'analyse de corrélation des essais sont présentés. Une corrélation raisonnable existe entre LHD et UCS pour le grès. Les résultats montrent que le test de dureté Leeb peut être particulièrement utile pour l'estimation du champ de UCS. La méthode est simple, rapide et les coûts d'équipement sont faibles. L'essai de dureté ne peut pas remplacer les tests UCS mais peut compléter ces tests, en particulier si les données sont nécessaires immédiatement ou autres tests est pas possible. 1 INTRODUCTION The unconfined compressive strength (UCS) of rock is a very important parameter for rock classification, rock engineering design and numerical modeling. In addition, this property is essential for judgment about the rocks suitability for various construction purposes. However, determination of rock UCS is relatively time consuming and expensive for many projects. Consequently, the use of a portable, fast and cost effective index test that can reasonably estimate UCS would be desirable. Other index tests, such as the Schmidt hammer and Point Load Test are commonly used for this purpose. However, this work looked at the Leeb Hardness Tester (LHT) which is quick, inexpensive and nondestructive: particularly valuable at preliminary project stages. The LHT method was introduced in 1975 by Dietmar Leeb at Proceq SA (Kompatscher, 2004). The LHT is a portable hardness tester originally for measuring the strength of metallic materials. Recently, it has been applied to various rocks for testing their hardness (e.g. Aoki and Matsukura, 2007; Viles et al., 2011), it can also be correlated with rock UCS according to Kawasaki et al., 2002; Aoki and Matsukura, 2007. Moreover, it is used to assess the weathering effects on hardness values (Kawasaki and Kaneko, 2004; Aoki and Matsukura, 2007; Viles et al., 2011). The LHT can be used in laboratory or the field at any angle (Viles et al. 2011), since the instrument uses automatic compensation for impact direction. It is suitable for applications to cover a wider range of most rock hardness compared with the Schmidt hammer (Aoki and Matsukura 2007). The aim of this study is to investigate the statistical rel(HLD) and UCS for sandstone which is one of most uniform and consistent rocks. For this reason, the laboratory testing was carried out on sandstone and combined with other literature values to develop a database with a total of 45 test results. the LHT methodology was evaluated (sample size and the number of Leeb readings that comprise an average test result). Statistical analysis was carried out on the database and the results of correlation analysis from tests are presented. Reasonable correlations between LHD and UCS for sandstone were developed and their accuracy were assessed. The results show that the LHT can be particularly useful for field estimation of UCS and offer a significant improvement over the field estimation methods outlined by the ISRM (2007). The equations that relate HLD to UCS are simple, practical and accurate enough to apply. The method is fast, simple and equipment costs are low. Although the empirically rock strength predicted from the in-direct LHT results contain some level of uncertainty, but are of significant value for preliminary design. Moreover, it could be used on core to provide a continuous profile of estimated UCS in a borehole log with minimal effort for UCS even beyond the preliminary engineering stage.

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