Assessing water-induced changes in tensile behaviour of porous limestones by means of uniaxial direct-pull test and indirect methods

Abstract

Understanding the uniaxial tensile behaviour of rocks and its water-induced variation are key issues for designing effective mining and civil engineering structures and for assessing numerous geotechnical hazards. However, these aspects remain poorly analysed because conducting uniaxial direct pull tests is a difficult and time-consuming laboratory task that requires the use of sophisticated equipment and complex rock sample preparation and processing. This work attempts to expand knowledge by determining several tensile properties of three porous limestone lithotypes under dry and water-saturated conditions through two different approaches: by conducting direct tensile tests and by means of indirect methods (i.e. Brazilian and point load tests). The results revealed that water saturation generated important reductions in their uniaxial tensile strength (UTS), tensile elastic modulus (Et), Brazilian tensile strength (BTS) and point load strength index (Is(50)). In addition, their petrological characteristics and mineralogical composition are used to discuss the main causes of the observed tensile softening. Furthermore, highly accurate correlation functions were established between the direct tensile strength parameters (UTS and Et) and the indirect ones (BTS and Is(50)) for the whole set of tested rocks. The proposed relationships are a novel and useful contribution to geomechanics because they enable the estimation of pure tensile parameters using alternative, cheap, rapid and versatile tests.