Discrete Element Modelling for biocemented sand: effect of calcite distribution at the microscopic scale

Abstract

The mechanical efficiency of the biocementation process is directly related to the microstructural properties of the biocemented soil, such as, the volume fraction of calcite, its distribution within the pore space (whether localized at the contact between grains or over the grain surfaces) and the contact properties: coordination number, contact surface area, contact orientation, type of contacts (frictional even after treatment, purely cohesive via a calcite bridge or combining friction between particles and cohesion of the localized calcite). Dadda et al, (2018) have used microscopic properties computed from 3D images obtained by X-ray tomography of biocemented sand samples with different levels of biocementation as an input in current analytical models to estimate the elastic properties (Young’s and shear modulus) and the strength properties (Coulomb cohesion). They pointed out the important role of some microstructural parameters, notably those related to the contact, on such effective parameters. However, the precise evaluation of the effect of microstructural parameters such as the contact surface distribution on the global mechanical behaviour of the soil requires the use of more advanced modelling methods. The paper presents the results of Discrete Element Modelling of triaxial tests with the open source code Yade in which the real microstructural properties of biocemented soil computed on 3D X-ray microtomography images are used as input parameters. A particular attention has been paid to take into account the actual distribution of contact surface in the model and not only the average value. It appears that the model is then able to reproduce the evolution of the macroscopic properties (in particular that of the cohesion) with the calcite content.