City Research Online

Abstract

This study investigates the grain scale mechanisms that lead to failure by strain localisation in a slightly cemented sandstone. While the effects of interparticle 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 a soft sandstone during triaxial compression to failure. The material studied is Fontainebleau sandstone, a quartzite formation from the Paris Basin, with a porosity of 21 %. Fontainebleau sandstone is a uniformly graded material with a mean grain size of 260 m. Triaxial compression tests at confining pressures of 2 MPa and 7 MPa were conducted on dry cylindrical specimens of 11 mm diameter by 22 mm 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 8.5 m (0.033d50) allowing a clear identification of the grains. A preliminary analysis has suggested that the failure mechanisms can be different for the samples tested at different confining pressures, which has a direct implication on the permeability of the material.

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

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