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Topic

Influence of Soil Structure and Fluid Physicochemical Properties on Surface Erosion of Cohesive Soils

Department of Civil Engineering

Date & location

• Wednesday, December 4, 2024
• 12:30 P.M.
• Engineering Office Wing
• Room 230

Reviewers

Supervisory Committee

• Dr. Cheng Lin, Department of Civil Engineering, University of Victoria (Supervisor)

• Dr. Min Sun, Department of Civil Engineering, UVic (Member)

• Dr. Peter Oshkai, Department of Mechanical Engineering, UVic (Outside Member) 

External Examiner

• Dr. Wenbo Zheng, School of Engineering, University of Northern British Columbia 

Chair of Oral Examination

• Dr. Neil Ernst, Department of Computer Science, UVic 

Abstract

Surface erosion is a process of removing soils and rocks from the ground surface, riverbeds, and seabeds by flows and currents, which pose significant threats to the safety of infrastructure and human well-being. This issue is exacerbated by global warming, resulting in increasing precipitation, rising sea levels, and the growing frequency of floods, storm surges, and hurricanes. While internal erosion has been extensively by the geotechnical community, particularly in the context of dam safety, surface erosion has been generally overlooked. In particular, a considerable gap exists in understanding surface erosion from a geotechnical perspective, especially for cohesive soils.

This study aims to assess the influence of soil structure and fluid physicochemical properties on the surface erosion of cohesive soils. A custom-built Rotating Surface Erosion Apparatus (RSEA) was developed at the University of Victoria in the absence of a relevant ASTM testing standard. Extensive element-scale experiments were conducted using the RSEA to examine the erodibility of cohesive soils with varying fine contents, water contents, and stress conditions. The effects of fluid physicochemical properties on soil erosion were also evaluated. In the end, a surface erosion erodibility model for cohesive soils was proposed based on the conservation of energy.

The findings of this research indicate that soil erodibility was influenced by both soil structure and fluid physicochemical conditions. An increase in the void index resulted in higher soil erosion resistance, whereas the unloading process increased soil erosion susceptibility. An inverse proportional relationship was observed between soil erodibility and the over-consolidation ratio (OCR). This relationship became insignificant once the OCR exceeded 4. Under identical hydraulic conditions, the erosion rate of natural soil was found to be 38% lower than that of laboratory-reconstituted soil. Additionally, fluid temperature was shown to primarily affect soil erodibility through physical processes, independently of pH and salt concentrations. Under low salt concentration conditions, soil erosion rates rose by up to ninefold as pH increased from 3 to 11. However, under high salt concentration conditions, erosion rates showed minimal variation with pH changes. Finally, the proposed erosion model was validated against the experimental data obtained from the RSEA, showing reasonable agreement.