Optical visualization of the full-field swelling of laminated rocks

Swelling laminated rock exhibits inherent anisotropy due to the preferred orientation of mineral grains and/or cracks which consequently impact its deformation behavior in terms of strain distribution and crack pattern during water-rock interaction (WRI). The classical method of measuring swelling deformation with dial gauges can not reveal the complex process of strain accumulation and the complex characterization in such interaction of water-anisotropic rock. In this work, we applied optical techniques along with image processing to measure tensile strain development across the surface of laminated rocks with various lamination angles under unconfined swelling testing conditions, thereby investigating their swelling behavior. Full-field strain development was monitored over time and the role of lamination in the overall expansion of the samples was identified utilizing the digital image correlation (DIC) technique. The results show that the tensile strain is distributed at the laminations and localizes at the cracks formed during imbibition. The direction of laminated rock expansion is perpendicular to the lamination and independent of the angle of the lamination. Laminated rocks preferentially crack in the lamination plane during free imbibition and form cracks that intersect the lamination planes at a small angular angles.