Direct Tensile Test on Brittle Rocks with the Newly Developed Centering Apparatus

Abstract

Failure of brittle rock normally initiates from tensile fracture due to its extraordinary lower resistance to tension rather than to compression. Intensive study on the deformability and accurate acquirement of the mechanical properties of rock under tensile stress is crucial for the stability analysis of rock slope and rock caverns. A new set of centering apparatuses, which consist of the specimen bonding part and the axial pulling part, were developed in this study. The misalignments when bonding the specimen and conducting the uniaxial tensile test can be effectively eliminated. Direct tensile tests were conducted on various brittle rocks cored from several large-scale hydropower station sites in China. The tensile strength, tensile elastic modulus, maximum tensile strain, and complete stress-strain curves were successfully obtained. The direct tensile test results indicated that the fracture surface formed in the central part of the specimen, which was under uniform tensile stress. The fracture surfaces were mostly perpendicular to the specimen axis. Fresh fractures without accumulation of rock fragments can be observed and characterized as tensile brittle failure. The microscopic failure modes of brittle rocks under the direct tensile test were not unique but consisted of the intragranular and intergranular fractures. The direct tensile strength (DTS) was generally lower than the Brazilian tensile strength (BTS) (DTS/BTS = 0.60~0.71). The direct tensile test was therefore recommended for the measurement of the tensile mechanical properties in order to ensure the safety of rock engineering.

Loading Rate Effect of Rock Material with the Direct Tensile and Three Brazilian Disc Tests

“…To carry out the direct tensile test, the bond and centring device (see Figure 1) was used in this research [28,29]. is device can effectively solve the eccentric problem of the rock specimens.…”

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

“…However, the mechanical response of these geomaterials under tensile stress and its water-induced variation have been poorly analysed due to the difficulties in tensile testing (Briševac et al, 2015;Hashiba and Fukui, 2015;Okubo and Fukui, 1996). This is a relevant research topic because the tensile failure of rock masses is the main failure mode in engineering practice (Huang et al, 2021;Liao et al, 1997;Zhang et al, 2018). In particular, an understanding of the rock behaviour under tension is of paramount importance in the design, execution and stability analysis of underground structures such as galleries, mining roofs, storage caverns, tunnel boring, drilling or blasting (Coviello et al, 2005).…”

Horizontal Compression Test: A Proposed Method for Indirect Determination of Tensile Strength of Stiff Soils and Soft Rocks

“…Several solutions have been adopted to address the aforementioned problems, such as preparing the specimen in a dumbbell shape (e.g., Tolooiyan et al, 2014;Demirdag et al, 2019) or etching a notch on the surface to force the specimen to fracture at the middle portion, using special connectors between the specimen and the loading frame (e.g. Fairhurst, 1961;Hawkes and Mellor, 1970;Okubo and Fukui, 1996;Perras and Diederichs, 2014), and using a centering apparatus (Zhang et al, 2017). Some of these techniques are effective, but complicated and expensive (Mellor and Hawkes, 1971;Butenuth et al, 1993;Coviello et al, 2005).…”