The dredging world is continuously growing, improving and adjusting to new challenges. As the demand for sustainable dredging practices grows and the availability of sand declines, the industry is increasingly exploring alternative materials, including fine-grained soils. This transition presents new challenges, particularly in understanding the behavior of these soils during dredging and reclamation. When stiff cohesive soils are dredged, they often form large lumps or balls, which are subsequently transported and deposited within a reclamation fill alongside a slurry.

The deposited clay lumps create a matrix with significant inter-lump voids, forming a double porosity system, consisting of these inter-lump voids and the voids within the lump, that significantly affects settlement predictability. Current settlement calculation methods typically assume a uniform layer, with soil parameters derived from the soil parameters of dredged material, which are later adjusted based on field feedback. This approach introduces substantial uncertainty, potentially leading to greater risks and increased costs.

This thesis investigates the complex deformation behavior of stiff, lumpy double porosity fills by performing both field data analysis and controlled experimental research. Field observations, including Cone Penetration Tests (CPTs), borehole data, and settlement plate measurements from a real-world reclamation project, are used to evaluate existing settlement models and the limitations of current design assumptions. In parallel, an experimental campaign involving oedometer testing and micro-CT scanning was conducted on clay lumps of varying undrained shear strengths($S_u$) to quantify deformation of macro- and, micro-voids and softening effects.

Findings reveal that traditional 1D-consolidation models, based on homogeneous assumptions, underestimate settlement magnitudes and rates during early loading phases dominated by macro-void collapse. Macro-void closure was observed to occur primarily under vertical effective stresses between 0.5 - 2 $S_u$, after which the fill behaves more homogeneously but remains structurally heterogeneous at the micro-scale. Experimental results highlighted the influence of lump strength and softening processes on overall deformation, with weaker lumps exhibiting void collapse at lower stress levels.

The study concludes that accurate settlement prediction of lumpy fills requires explicit consideration of initial macro-structure collapse, evolving lump strength, self-weight consolidation, and heterogeneous stress transfer. While conventional isotache-based models remain suitable after macro-void closure, early-stage design should incorporate adaptive, probabilistic approaches. Recommendations for future research include refining laboratory testing protocols, improving imaging resolution for micro-structural tracking, and expanding long-term monitoring to better understand the time-dependent evolution of lumpy fills under field conditions.