Micromechanical Model of Wet Granular Material

Landslides are one of the main natural threats for both people and infrastructure in mountainousregions. In most cases, landslides are triggered by the loss of cohesion in a soil due to the increasingwater saturation level after long or intense rainfalls. Only little is known on the triggering of failuresat the microscopic scale due to the limited experimental accessibility and the lack ofmicromechanical models that capture the granular mechanics and the fluid transport in the pore spacefor the relevant saturation levels simultaneously [3].We study this problem by a discrete model approach based on contact dynamics, where forcesexcreted from a liquid phase add to the motion of spherical particles. The model can deal witharbitrary saturation levels, ranging from the capillary bridge regime to the fully saturated state. Toaccount for water in the pore space we develop a geometrical pore-scale model similar to the modelsproposed recently by Gladkikh [2] and Motealleh [3]. In our model, we allow the formation ofisolated arbitrary-sized water clusters which can have different Laplace pressures and exchange waterthrough water films on the grain surface. These clusters can grow in size, shrink, merge and split,depending on local conditions and changes of accessible water and the pore space. We calculate thefailure envelope for the dilatant material under multi-axial loading, considering possiblerearrangements of particles and fluid interfaces at changing saturation states. REFERENCES[1] Mani, R., Kadau, D., Or, D. and Herrmann, H.J.: Fluid depletion in shear bands, PhysicalReview Letters 109 (2012), 248001. [2] Gladkikh, M. and Bryant, S.: Prediction of imbibition in unconsolidated granular materials,Journal of Colloid and Interface Science 288 (2005), 526-539. [3] Motealleh, S., DiCarlo, D. and Bryant, S.: Unified Model of Drainage and Imbibition in 3DFractionally Wet Porous Media, Transport in Porous Media 99 (2013), 581-611.