Application of microbially induced calcite precipitation in erosion mitigation and stabilisation of sandy soil foreshore slopes: A preliminary investigation

Abstract

Eroding foreshores endanger the floodplains of many estuaries, as such, effective and environmentally friendly interventions are sought to stabilise slopes and mitigate erosion. As a step in forestalling these losses, we developed laboratory microcosms to simulate tidal cycles and examined the mechanisms of erosion and failure on sandy foreshore slopes. As an experimental aim, we applied microbially induced calcite precipitation (MICP) to selected slopes and compared the effectiveness of this microbial geo-technological strategy to mitigate erosion and stabilise slopes. To assess shoreline stability, thirty cycles of slowly simulated tidal currents were applied to a sandy slope. Significant sediment detachment occurred as tides moved up the slope surface. For steeper slopes, one tidal event was sufficient to cause collapse of the slopes to the soil's angle of repose (~35°). Subsequent tidal cycles gradually eroded surface sediments further reducing slope angle (on an average 0.2° per tidal event). These mechanisms were similar for all slopes irrespective of initial slope inclination. MICP was evaluated as a remedial measure by treating a steep slope of 53° and an erosion-prone slope angle of 35° with Sporosarcina pasteurii and cementation solution (0.7 M CaCl2 and urea) before tidal simulations. MICP produced 120 kg calcite per m 3 of soil, filling 9.9% of pore space. Cemented sand withstood up to 470 kPa unconfined compressive stress and showed significantly improved slope stability; both slopes showed negligible sediment erosion. With efforts towards optimisation for upscaling and further environmental considerations (including effect of slope saturation on MICP treatment, saline water and estuarine/coastal ecology amongst others), the MICP process demonstrates promise to protect foreshore slope sites.

Review of the use of microorganisms in geotechnical engineering applications

“…In a study to mitigate soil erosion [146], a maximum increase of 0.6 MPa in the UCS of a soil treated with MICP was obtained. Studies by Jijian [147] revealed an improvement in the UCS of a sand column of up to 1.91 MPa after employing a biogrouting method which effectively hardened black sands.…”

Bio‐mediated soil improvement: The way forward

“…In another case, MICP was found to have the potential to simultaneously immobilize heavy metals in a brownfield soil as well as strengthening the soil for construction purposes (Jiang, Liu, Du, & Bi, 2019a). Other multi-functional applications of MICP including shoreline protection (Salifu, MacLachlan, Iyer, Knapp, & Tarantino, 2016), geological hazard mitigation (Jiang, Tang, Yin, Xie, & Shi, 2019b), soil and water conservation, and pollution control for radionuclides are also under active research, though mostly at a preliminary stage. Nevertheless, more research effort is needed to develop multifaceted MICP protocols that could address multidisciplinary engineering challenges by coupling soil engineering performance enhancement with ecological, environmental and carbon footprint benefits.…”

Feasibility Study of Native Ureolytic Bacteria for Biocementation Towards Coastal Erosion Protection by MICP Method

“…Therefore, sustainable and eco-friendly materials and systems are in demand for the protection against coastal erosion. Countermeasures against coastal erosion protection have been studied by many researchers [1], including hard and soft structures focusing on urea degradation bacteria. However, all these methods have an adverse effect on the surrounding landscape, environment, and ecosystem [2]; moreover, eco-sustainability is another major concern.…”