A procedure for determining long-term creep rates of soft clays by triaxial testing

The paper presents a procedure for determining a significantly larger range of creep rates (isotaches) of soft clays than found from standard incremental loading oedometer tests. The test is performed in a triaxial apparatus by first loading up to the virgin compression line at a relevant effective stress level and then determine the creep rates at different stress states along an unloading branch keeping the horizontal to vertical effective stress ratio constant. The test procedure is tested on a soft Norwegian plastic marine clay. Challenges due to the non-linear behaviour of natural soft clays where the standard creep and compression indexes are not constant values are demonstrated, and recommendations for how to account for this effect are given. The obtained results from the test are also compared with results from a parallel long-term creep phase in a standard oedometer apparatus taken from the same block sample

Micro-level investigation of the in situ shear vane failure geometry in sensitive clay

The circumferential failure surface of a shear vane in strain softening soft sensitive clay is studied. A set of shear vane experiments are performed in situ, where the sheared region is retrieved from the ground using an over-coring technique. By producing thin sections, the circumferential failure zone is revealed when viewed under a polarised light microscope. The failure zone is found to first evolve after reaching the peak global resistance. Its shape is not a full cylinder, but rather a rounded square. The structure of the shear zone is non-smooth and characterised by complex shear patterns of micrometre size

Time- and stress-compressibility of clays during primary consolidation

The existence of creep deformation during primary consolidation has been widely accepted; however, there are still contradicting opinions on the mechanisms that govern creep during the primary consolidation phase. This study aims to assess creep effects during primary consolidation such that it is possible to critically evaluate and challenge some of these opinions. A special type of interconnected oedometer tests were designed and conducted. The tests were numerically studied using a soil model based on the isotache concept. These analyses show that the isotache concept can capture the important features of the tests well and thereby describe the time- and stress-compressibility of a soil during the entire soil compression phase

Time- and stress-compressibility of clays during primary consolidation

The existence of creep deformation during primary consolidation has been widely accepted; however, there are still contradicting opinions on the mechanisms that govern creep during the primary consolidation phase. This study aims to assess creep effects during primary consolidation such that it is possible to critically evaluate and challenge some of these opinions. A special type of interconnected oedometer tests were designed and conducted. The tests were numerically studied using a soil model based on the isotache concept. These analyses show that the isotache concept can capture the important features of the tests well and thereby describe the time- and stress-compressibility of a soil during the entire soil compression phase

A generalized 3DLS-DEM scheme for grain breakage

We introduce a new generalized 3DLS-DEM (3D Level Set Discrete Element Method) scheme that incorporates grain breakage, taking an important step towards realistic modeling at the micro-scale with DEM. For the first time, simulating thousands of real 3D grains that are able to break, which was possible due to the algorithm used for grain breakage. The presented scheme is not only capable of efficiently simulating grains with real shapes but also preserving mass and grains morphology with high fidelity when breakage occurs. Hence, with this approach, further works within the original 3DLS-DEM scheme could take into account other physical phenomena at the grain-scale such as electrostatic induced cohesion, heat transfer, or the presence of a fluid, etc. On the other hand, the breakage process modified grain size and roundness distributions, which, in turn, might change the strength and critical state of the sample. Withal, the overall process seems to suggest that grain breakage may be a sufficient condition to exacerbate the prevalence of shear banding within the sample. Finally, our model is able to perform breakage on several real 3D grains of a sample consisting of thousands of grains in a generalized 3DLS-DEM scheme