Multi-scale characterisation of sensitive clays

Licentiate thesis, 2026

Quick clays are highly sensitive fine-grained sediments that can undergo a pronounced and irreversible loss of shear strength when disturbed, potentially leading to progressive failure and large ground displacements. In Sweden, where glacial and post-glacial fine grained deposits are widespread, the processes responsible for the emergence of high sensitivity remain insufficiently resolved, particularly under natural saturated conditions, where conventional characterisation methods may disturb the intact structure of the clay. This thesis addresses that research gap by combining physicochemical and compositional analyses, liquid-limit testing under different ionic conditions, wide-angle X-ray scattering (WAXS), nano X-ray Computed Tomography (nano-tomography), and rheological testing to investigate natural sensitive clays in the saturated state. The work focuses on identifying
the conditions associated with strain softening upon remoulding and on identifying the length scale at which relevant changes between intact and remoulded states become discernible. Particular emphasis is placed on non-destructive characterisation methods that avoid dehydration-induced artefacts.
The results show that pronounced strength loss cannot be attributed to a single controlling factor. Instead, high sensitivity is best understood as the outcome of coupled effects involving pore-water chemistry, mineralogical assemblage, saturated fabric, and interparticle bonding. Among these factors, pore-water chemistry emerged as particularly important, influencing both index behaviour and changes in the structure at nanoscale, with lower ionic concentrations generally associated with higher sensitivity in the clays investigated. Liquid limit testing further showed that the response to changes in pore water chemistry depends on mineralogical composition, supporting the interpretation that physicochemical effects on sensitivity vary with clay mineralogy. Nano-tomography resolved macropores and coarse particles in the saturated clay matrix, but differences between intact and remoulded states were not consistently captured at the achieved resolution, indicating that the critical changes associated with strength loss occur pre
dominantly at smaller scales. Rheological testing further showed that progressive strain softening can be probed systematically.
Overall, the thesis contributes to a process-based interpretation of the emergence of high sensitivity in natural clays by linking physicochemical conditions and multi-scale characterisation in the saturated state. It also provides a scientific basis for future work aimed at resolving nanoscale processes during shearing and leaching, and ultimately at reproducing key features of quick clay behaviour under controlled laboratory conditions.