Empirical strenqth envelope for shale

Abstract

Effectively, strength envelope describes behavior of a rock body when subjected to common stresses in construction, namely compressive, tri-axial and tensile. This study is aimed at investigating the strength envelope for shale, a sedimentary rock obtained from dam project site in Baram, Sarawak. Series of triaxial compression tests were carried out to obtain the strength envelope for the rock samples. For verification of failure criterion, uniaxial compression and Brazilain tests were also conducted on the rock samples. Results from the related tests were analysed using RocData software to obtain the strength envelope. Subsequently, Mohr-Coulomb and Hoek-Brown failure criterion are used to determine failure envelop for the rock samples. Based on the failure envelopes and the related strengths (i.e. compressive and tensile strength), suitability of both approach, in defining strength envelope for shale, is verified. The study shows that for highly laminated sedimentary rock like shale, Hoek-Brown criterion gave a more representative failure behaviour. The failure envelope clearly shown all the strength limits when the rock subjected to triaxial, uniaxial and tensile stress, which is not observed in Mohr-Coulomb. Hoek-Brown criterion is more superior for describing rock body as mass strength rather than material strength.