Effect of Bio-Cementation on Wave-Induced Pore Water Pressure in Sand

Coastal dunes are protective structures and shield coastal communities and infrastructure from inundation, particularly during intense storms. However, the buildup of wave-induced pore water pressure in sandy soil can lead to localized regions of liquefaction, ease soil particles to detach, and facilitate erosion, ultimately causing failure. A two-dimensional sand profile has been numerically modeled and subjected to repeated wave loading to investigate the wave-induced pore pressure regime in the soil. Oscillatory and residual soil responses are the causes of pore pressure in the soil during storms. The oscillatory pore pressure is due to the water pressure fluctuation at the seabed under the wave loading and can cause momentary liquefaction. Due to wave-induced cyclic shear stress, the principal stress orientation rotates continuously and can accelerate plastic deformations and, therefore, buildup residual pore pressure. This study used equilibrium and continuity equations, including a source term, as the governing equation for predicting the residual and oscillatory components' pore water pressure due to repeated wave loading. As bio-mediated soil improvement techniques are being adopted to improve the shear strength and stiffness of soil, the microbially induced calcite precipitation (MICP) treatment was applied to the surface of the soil to reduce the impact of wave-induced instability of the slope. This study incorporated bio-cementation parameters into the equations mentioned above to capture the pore pressure response within the treated soil. The numerical results indicate that the bio-treated layer decreases the upward pore pressure gradient in the susceptible region close to the ground surface. Moreover, due to shear strength improvement, the rate of pore pressure generation in treated soil is significantly lower than in untreated soil.