Utilization of the Brazilian test for estimating the uniaxial compressive strength and shear strength parameters
K Karaman, F Cihangir, B Ercikdi, A Kesimal, S Demirel
Uniaxial compressive strength (UCS) and shear strength parameters
(cohesion and angle of internal friction, C and f) of rocks are important
parameters needed for various engineering projects such as tunnelling and
slope stability. However, direct determination of these parameters is
difficult and requires high-quality core samples for tests. Therefore, this
study aimed to explore the applicability of the Brazilian test (BT) – a
simple, less sophisticated and inexpensive method for both specimen
preparation and testing – to estimate the UCS and shear strength
parameters of rocks. Thirty-seven rock types were sampled and tested, 24
of which were volcanic, 8 were metamorphic, and 5 were sedimentary.
Statistical equations were derived to estimate the UCS and shear strength
parameters of rocks using the BT. The validity of the statistically derived
equations was confirmed using predictive analytics software (PASW
Statistics 18). A strong linear relation was found between BT and UCS
values. BT and UCS values exhibited prominent linear correlations with
the cohesion values of rocks. The Mohr envelope was also used to
determine the cohesion and friction angle of rocks using BT and UCS
values. It is deduced from the current study that the BT values can be used
to estimate the UCS and cohesion. However, no relation was observed
between the angle of internal friction values and the UCS and BT for all
rock types. Therefore, different approaches are suggested for the
estimation of the internal angle of friction for application in the
preliminary design of projects.
Keywords: Brazilian test, shear strength parameters, triaxial compressive strength,
uniaxial compressive strength, Mohr-Coulomb criterion