, Volume 53, Issue 5, pp 871-882

Characterization of Mechanical Behaviour of Saturated Sandstone Using a Newly Developed Triaxial Apparatus

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Abstract

Triaxial testing is a reliable and popular test method used to obtain key properties of rock and soil used in geotechnical design and numerical modelling. Testing equipment should be sufficiently equipped to accurately simulate the in-situ stress state and hydrogeological conditions of the specific design region. However, detailed information on the specifications and development of versatile triaxial apparatuses for testing rock to a high degree of accuracy has rarely been reported in the literature. This paper describes details of a triaxial apparatus developed for testing intact and jointed rock. The newly developed apparatus is able to obtain information regarding stress-strain behaviour, pore fluid pressure changes, volume changes, permeability and crack development behaviour of the test specimen. Following the description of the triaxial apparatus, results of a series of undrained triaxial tests performed on Hawkesbury sandstone specimens at different confining pressures (i.e. 2, 5, 8, 10, 12, 18 and 25 MPa) and a constant pore water pressure of 1 MPa, are presented. At lower confining pressures the sandstone showed more brittle characteristics and at higher confining pressures (i.e. greater than 18 MPa) it showed a more ductile behaviour. Mohr-Coulomb diagrams showed a decline in friction angle with increasing confining pressure. Maximum induced pore water pressure was increased linearly with increasing initial effective confining pressure. Volumetric strain variations showed a significant dilation at lower confining pressures with a considerable volume increase. Permeability exponentially decreased with increasing confining pressure. Acoustic emission data revealed that crack initiation occurred close to the peak stress for specimens tested at low confining pressures but it occurred at much lower stresses in specimens tested at higher confining pressures.