Bio-Cementation for Structural and Thermal Soil Enhancement with Retained Hydraulic Conductivity

In hot, dry climates, geothermal systems often underperform due to low soil thermal conductivity and heat capacity. Periodic water ingress helps restore both, enabling more effective ground heat transfer. Remediation must therefore improve thermal and mechanical properties without blocking flow. This study tests whether bio-cementation can achieve that balance. We combined unconfined compressive strength, thermal and hydraulic conductivity testing with X-ray computed tomography and flow modelling to track microstructural evolution during microbial and enzyme induced carbonate precipitation (MICP and EICP). While final CaCO₃ distributions were visualized across all strategies, we captured time-lapse 3D X-ray imaging of soybean EICP for the first time, showing that precipitation at grain contacts enhanced strength and thermal conductivity while preserving flow pathways. In contrast, MICP provided comparatively uniform thermal conductivity enhancement before clogging at nine cycles. Jack bean meal achieved the highest thermal conductivity increase (up to 781%), but this enhancement was highly localized. In contrast, soybean EICP produced more uniform CaCO₃ precipitation, yielding consistent thermal conductivity gains (~600%) and an unconfined compressive strength of 17.9 MPa at 26.6 wt% CaCO₃. Soybean curds reduced hydraulic conductivity but conferred no significant improvement in thermal or mechanical performance. These findings support targeted bio-cementation strategies that enhance subsurface thermal functionality without compromising flow, with direct applications in energy piles and geothermal systems in arid climates. • Soybean EICP reached 17.9 MPa UCS while retaining permeability over 25 cycles. • Time-lapse XCT tracked CaCO₃ growth and flow changes across EICP cycles. • Thermal conductivity increased up to 781% via EICP. • Soybean EICP formed thermal bridges by CaCO₃ layering at grain contacts, seen in XCT. • Organic additives lowered permeability without improving thermal conductivity in EICP.