The Effect of Level of Cementation and Geometry on Stability of Cemented Coastal Bluffs and Slopes

Coastal bluff erosion and recession are among the common mechanisms altering the geomorphology of the coastline in California. The accelerated erosion rate increasingly threatens the stability of structures located on these bluffs. Previous researchers have investigated the effect of material properties and strength on the generation of the shear plane and failure modes of coastal bluffs and cliffs. Monitoring the morphology of the moderately cemented coastal bluffs with time has indicated that a comparison of material strength with the expected in situ minor principal stress distribution can be used as a criterion to assess bluff stability. However, the effect of varying factors such as cementation levels and bluff geometry and dimensions on stress distribution patterns and material properties that determine bluff failure susceptibility requires further investigation. While bond breakage and disturbance during sampling and transportation undermine the quality of recovered soil samples, artificial cementation methods (e.g., Portland cement) may not properly replicate the natural formation processes. Instead, microbially induced carbonate precipitation (MICP) is a ground improvement method that simulates the cementation processes that occur in natural geological settings. This method harnesses the activities of bacteria to generate cementitious precipitation among soil particles. The formation of the cementing agent improves the mechanical properties of the soil. In the past two decades, extensive studies have been devoted to understanding the cementation formation mechanism and the improvement of mechanical properties that can be used as a proxy for natural cemented soil for stability analysis. In the study presented herein, a series of FEM models were developed in SIGMA/W software. The effect of the different cementation levels and variation of bluff geometry on minor principal stress distribution was investigated. Results of the study demonstrated that although the cementation level of the materials determines the failure mode, the stress distribution mainly depends on the bluff geometry. The obtained results offer further insights into the failure mechanism of coastal bluffs as well as MICP-treated slopes for future field implementation of this soil improvement method.