Biologically induced rock modifications harness biogeochemical activities to influence the properties and behavior of surrounding rock mass. It often relies on bio-mediated reactions, such as enzyme-induced carbonate precipitation (EICP), which utilizes biomineralization by promoting the formation of calcium carbonate (CaCO3) in rock discontinuities. Yet, there is still a lack of knowledge on the impact of bio-mediated methods (such as EICP, biopolymers) on the hydraulic properties of rock masses at varying scales. Additionally, there is no understanding of how biomineralization mechanisms at the pore-scale can be mapped to the bulk-scale spatial distribution and flow path property modification. Therefore, this study uses non-destructive methods to investigate the micro- (localized) and macro- (bulk) scale effect of biological-induced alterations on the pore volume (porosity) and flow pathways (permeability) in rock masses, and to quantify its impact on pore networks, and validate identified changes with scale-bridging evidence. The results demonstrate that both EICP and biopolymer treatments can significantly modify the hydraulic properties of rock, with distinct effects observed across scales. EICP reduced porosity by 46% at the micro-scale and 7% at the macro-scale, while biopolymer treatment led to porosity reductions of 18% and 2% at the micro and macro scales, respectively. In terms of permeability, EICP exhibited a more pronounced impact, decreasing macro-scale permeability by 68% in EICP compared to 32% for biopolymer, and micro-scale permeability reduction by 18% EICP versus 11% biopolymer. The greater reduction in macro-scale permeability is attributed to preferential bio-clogging near the specimen surface and obstruction of primary flow channels that dominate bulk fluid movement. Additionally, EICP’s superior effectiveness is linked to calcium carbonate (CaCO₃) mineralization along pre-existing discontinuities, in contrast to the biopolymer’s soluble mucilaginous matrix. Accordingly, this work proposed effective fracture spacing as a novel, scale-bridging metric that captures the reduction in hydraulically active pore networks and fractures due to biocementation, even when geometric fracture spacing remains unchanged. These findings provide new insight that advances understanding of porosity-permeability decoupling and informs the design of nature-based engineered solutions for flow control in geomaterials.
Ngoma et al. (Fri,) studied this question.