Experimental investigation of capillary collapse of partially saturated granular soils during saturation

• Applicant: Professor Dr.-Ing. Jürgen Grabe
• Subject Area: Geotechnics, Hydraulic Engineering
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 516409567

The objective of the second project phase is to formulate a constitutive model for the capillary collapse of granular soils with bimodal porosity within a continuum mechanics framework. Capillary collapse is defined as an irreversible volumetric deformation triggered by an increase in the degree of saturation of unsaturated soils. This phenomenon is governed by several interacting factors, including irrigation conditions, the applied stress state, and the porosity of the soil. The ongoing first project phase has already provided an extensive experimental basis, ranging from macroscopic tests to particle-scale investigations. These studies have demonstrated that capillary collapse is strongly linked to soil water retention behaviour and to the imposed boundary conditions. In particular, the presence of porous lignite particles has been shown to influence the collapse mechanism. Therefore, evaluating soils with varying lignite contents is essential to capture the true extent of this effect. The main challenge now lies in developing a mathematical expression that integrates the governing factors and accurately predicts the magnitude of collapse. Achieving this will provide the foundation for predictive constitutive modelling. Using the comprehensive experimental dataset already available, the proposed work aims to derive, formulate, and validate a constitutive model that links bimodal porosity, water retention behaviour, and collapse mechanisms. This model will establish the basis for future computational applications and the extension of predictive tools in unsaturated soil mechanics.

• DFG Programme: Research Grants