City Research Online

Abstract

This study investigates the grain scale mechanisms that lead to failure by strain localisation in specimens of Fontainebleau sandstone with different degrees of cementation. While the effects of inter-particle bonding on the mechanical behaviour of granular geomaterials, including soft rocks, have been largely studied, the physical micro-scale mechanisms governing the material deformation are still poorly understood. In this study, laboratory techniques have been developed to allow a non-invasive investigation of the internal deformation of sandstones during triaxial compression to failure. The material investigated was Fontainebleau sandstone, a quartzite formation from the Paris Basin (France) which can be found as very hard, tightly cemented sandstone or more permeable and less cemented material. Specimens with porosities 6% and 21% were investigated. Triaxial compression tests at confining pressures of 2MPa and 7MPa were conducted on dry cylindrical specimens of 11mm diameter by 22mm height. Three-dimensional images of the full specimen were obtained by carrying out x-ray micro-tomography scans at key points throughout the test. The high-resolution tomographic images have a voxel size of 8.5um (0.033d50) allowing a clear identification of the grains. The analysis suggests that dilatancy of the material which depends on the degree of bonding between grains, plays a fundamental role on the failure mode of the granular media.

Publication Type:	Conference or Workshop Item (Paper)
Publisher Keywords:	fabric-structure of soils, soft rock, laboratory tests, x-ray micro-tomography
Subjects:	T Technology > TA Engineering (General). Civil engineering (General)
Departments:	School of Science & Technology > Engineering

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