Experimental investigation of the tensile failure of rock in extension

Abstract

ABSTRACT : This research has studied the behaviour of intact rock in extension, as observed by the behaviour of specimens of sandstone and marble. The thesis consists of four parts: the first part, presents a literature review of the behaviour of rock in extension, the fracture mechanics used to describe this behaviour and observations of natural fractures formed in extension. In the second part a new way of measuring the ultimate strength of rock in extension, the Hoop tension test, has been extensively investigated both in theory and in practice. Experimental investigations using photoelasticity, holography and SEM observations are used to corroborate the theoretical findings of the mathematical and FEM analyses relating to the tensile and compressive regions which exist in the hoop shaped specimens. The third part of the thesis is concerned with the application of the Hoop tension test to the behaviour of sandstone and marble in extension and the influence of rate of loading, saturation, hoop size and boundary conditions between rock and platens. This part concludes with a comparison of the results obtained from conventional tensile tests and the Hoop test. Part four is devoted to the conclusions of this research which may be summarised as follows: - the Hoop tension test provides a trustworthy and predictable method of failing rock in extension, and studying the behaviour of rock in extension. - rock behaviour in extension appears to be a far more sensitive indicator of the contribution that fabric and possibly mineralogy, and stored strained energy, may make to the mechanical behaviour of intact rock, than measures of cohesion, friction and stiffness gained from compressive shear.