Investigation of the effective hydro-mechanical properties of soil-rock mixtures using the multiscale numerical manifold model

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This study focuses on determination of the effective hydro-mechanical properties of a widespread geological mélange, the Soil-Rock Mixture (SRM), using the multiscale Numerical Manifold Method (NMM). Influences of the Volumetric Block Proportion (VBP), block size, block shape, block orientation angle and micro-dynamics on the effective properties are investigated thoroughly. The SRM structural models are generated within the NMM framework in a statistical manner. The effective properties are extracted using the multiscale theory where micro-dynamics is fully considered based on the extended Hill-Mandel lemma. Through numerical simulations, the VBP and block orientation angle prove to be the first and second most influential factors. A growing VBP leads to increasing deformation moduli but decreasing effective permeability and Biot’s factor. Normal components of permeability and deformation tensors are positively proportional to the corresponding normal intersecting areas formed by sample cross-sections and blocks while shear components are positively proportional to sums of the normal and shear intersecting areas. Introducing micro-dynamics and diminishing the time step make the effective permeability and deformation moduli rise while Biot’s coefficient decrease. The accuracy and stability of the multiscale NMM are validated by comparing present results with those of empirical formulae and single-scale numerical methods.