Evaluation of the single compressive strength test in estimating uniaxial compressive and Brazilian tensile strengths and elastic modulus of marlstone

Abstract

Uniaxial strength (UCS), tensile strength (BTS), and elastic modulus (E) are important rock strength parameters used in many engineering projects such as dam, bridge, and tunnel constructions. Several direct and indirect methods have been proposed to measure these parameters. For direct methods, standard samples should be prepared and loaded. Indirect methods are used to estimate these parameters when there is no access to the standard core for various reasons. In this regard, the single compressive strength test (SCS) is one of the indirect methods for estimating these parameters using small specimens. In the present study, the possibility of using SCS test for predicting strength parameters of marlstones is investigated. For this purpose, a total of 10 marlstone blocks were collected from different geological formations of Iran. After preparation of the standard samples, an attempt was made to determine uniaxial strength (UCS), Brazilian tensile (BTS), and elastic modulus (E) of each sample. Next, the samples were crushed and 50 small spherical particles with diameters of 3, 5, 8, 9, and 10 mm were prepared from each sample. A total of 500 particles were used for SCS testing. Then, the single compressive strength index (SCSI) was determined for each particle by plotting load-displacement diagrams; the SCSI of each sample was the average SCSI of 10 same size particles. Subsequently, UCS-SCSI, E-SCSI, and BTS-UCS correlations for specific particle sizes were proposed using the regression analysis. The mean values for the correlation coefficients were obtained as 0.93, 0.89, and 0.91, respectively. The empirical relationships were verified by conducting 100 tests on the control samples, which revealed the reliable validity of the outcomes. The results of this regression modeling, compared with the data obtained from SCS experiments on limestone and sandstone particles mentioned in the literature, demonstrated that the empirical relationships were affected by rock types. Therefore, rock-specific diagrams have to be drawn for particles with different lithologies.