Riverbank Stability under the Influence of Soil Dispersion Phenomenon

Erosion is one of the key factors in environmental management and river restoration. Different mechanisms influence riverbank stability and mass failure, such as seepage erosion. The present study investigates the effects of soil dispersion as one of the soil chemical properties on seepage erosion to evaluate the instability criterion for riverbanks. The middle Atrak River in Iran, where extensive riverbank erosion, seepage cavity, and lumped mass failure have been observed, was selected as a case study. Results indicated that there was significant correlation (r=0.90) between the soil dispersion and the volume of the seepage undercutting cavity. Further, the results of numerical simulations suggested that where the depth of the undercutting cavity was large, the safety factor of riverbank stability was about 25% less than that at a location with less undercutting. Attempts were also made to understand the effects of groundwater level on the stability of eroded riverbanks due to seepage. It was also observed that in locations with larger cavity dimensions, an increase in subsurface water table up to 3 m may cause the safety factor to be 5% higher than that at locations with smaller cavity dimensions, although this value is not significant in geotechnical engineering.