Impact of mineralogical features on the mechanical behaviors of granite: A study using physically informed 3D microstructural model

Mineralogical features, including mineral spatial distribution, shape, and orientation, are important in determining the mechanical behaviors of granite. This effect was investigated by using the X-ray micro-computed tomography (micro-CT) scan on granite specimens (10 mm diameter and 15 mm height) before and after uniaxial compressive strength (UCS) testing. The X-ray micro-CT scan generated thousands of CT images, which were processed using advanced digital image processing (DIP) techniques. Specifically, the Residual Network–Visual Geometry Group16–UNet (Res–VGG16–UNet) model and the circular threshold segmentation technique were applied to identify and map minerals within the CT images. The coordinate information extracted from these mapped minerals was then used to create 3D Subspring Network Breakable Voronoi (SNBV) microstructural models that incorporate the mineral characteristics of tested granite specimens. The models consist of a mesh (3D Voronoi tessellation) of rigid, breakable, Voronoi blocks. The extracted coordinate information, forming a large dataset, was managed by the k-Dimensional Tree (KD-Tree) algorithm to facilitate mineral type assignment in SNBV models. The models were calibrated by comparing their results with the experimental data obtained from UCS tests. This study further explored the variations in biotite grain spatial distribution, shape, and orientation within a calibrated SNBV model, and examined their impact on the UCS and fracture behaviors of granite, based on a set of simplified microproperties. The results illustrate that as the SNBV model resolution (defined by the number of rigid blocks contained in models with identical physical dimensions) increases, mechanical properties, including UCS and crack initiation and damage strains and stresses, reach constant values. Additionally, the spatial distribution, shape, and orientation of biotite grain affect the UCS of granite, while their effect on the failure strain is minimal. The aspect ratio of biotite grains affects UCS, with z-axis elongation (aligned with compression) yielding higher UCS than x-axis elongation (perpendicular to compression).