Determination of the Uniaxial Compressive Strength of Rocks from the Strength Index

Abstract

The uniaxial compressive strength (UCS) is classified as one of the basic mechanical properties of rocks, which is widely used in mining and construction practice. For example, it allows geomechanics to classify individual rocks and soils into groups with the same or similar mechanical properties. An example is the (RMR) Rock Mass Rating, Barton’s Q system. [1,2]. As a rule, only an indicative determination of the uniaxial compressive strength is sufficient for this classification. The uniaxial compressive strength is determined in the laboratory on regular test pieces. The preparation of these test bodies is often a time-consuming and costly process, and in some cases, the recommended shape cannot be prepared for a small amount of rock sample or, in the case of highly fractured and friable rock. For this reason, alternative methods for determining compressive strength are being sought. These methods are supposed to be faster and cheaper and to provide results directly in situ. The paper presents information obtained from the indirect determination of the uniaxial compressive strength according to the strength index measured with a field press on various rock types from the Czech Republic. Keywords: Point load index; Rock testing; Uniaxial compressive strength.