The enzyme-induced calcium carbonate precipitation (EICP) technique strengthens soil and reduces permeability by cementing soil particles with calcium carbonate. However

limited penetration of solutions between soil particles hinders cementation in saturated environments

necessitating systematic investigation of EICP reinforcement in underwater

unconsolidated sandy layers

such as seabed and lakebeds. In this study

we developed a model test system for underwater EICP grouting and implemented controlled pore-water flow in underwater sandy layers using a perfusion–drainage liquid cycle. During EICP reinforcement

we measured the conductivity

pH

and Ca concentration of the reaction solution in embedded and drainage pipes to characterize changes in mineralization efficiency in saturated sand. Additionally

by tracking the model’s overall permeability as a function of reinforcement cycles and applying electrical-resistance tomography

we systematically characterize reinforcement effects and the spatiotemporal evolution of grout diffusion in underwater sands. 1) The perfusion–drainage system enables EICP grouting reinforcement in water-rich sandy layers. The saturated-sand permeability decreases from 1.28×10 m/s to 9.66×10 m/s after 10 EICP treatments. 2) The slurry diffuses from both sides of the grouting pipe toward the center pumping pipe

with high conductivity

low pH

and Ca enrichment

indicating continued diffusion and mineralization as resistivity declines toward stabilization and pore space becomes filled. 3) Resistivity varies significantly with depth and location

indicating uneven reinforcement in large-scale soil masses. These findings provide a theoretical basis for applying EICP technology to seabed foundation reinforcement and submarine landslide mitigation.