Numerical Study on Bentonite Permeability Evolution upon Water Hydration

Water permeability plays a key role in many geomechanical problems, but its experimental determination in unsaturated conditions still represents a challenging task. Such complexity is even more evident when dealing with active clays, like bentonite. Bentonite primarily consists of montmorillonite and, when compacted, is characterized by a multi- porosity structure. Its microstructure evolves upon water saturation, influencing the hydro-mechanical response at the laboratory scale. Experimental evidences highlight how bentonite saturated permeability spans over several orders of magnitude in the range of the most common dry densities and significant permeability variation occurs upon desaturation and pore structure evolution. The present work aims to analyze and reproduce by mean of numerical simulations a set of experimental swelling pressure tests in isochoric conditions performed on bentonites characterized by different initial dry densities and initial microstructures (i.e. granular bentonite and compacted blocks). Taking advantage of numerical simulations, performed via the finite element codeLAGAMINE, the hydro-mechanical response of these bentonite assemblies is examined and a better understanding on the influence of the multi-porosity evolution on permeability is provided.