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Topic

Coupled Effects of Pore Fluid pH and Salinity on the Erodibility of Cohesive Soils

Department of Civil Engineering

Date & location

• Friday, December 12, 2025

• 9:30 A.M.

• Virtual Defence

Reviewers

Supervisory Committee

• Dr. Cheng Lin, Department of Civil Engineering, ӣ��Ӱ�� (Co-Supervisor)

• Dr. Min Sun, Department of Civil Engineering, UVic (Co-Supervisor) 

External Examiner

• Dr. Wenbo Zheng, NRES Graduate Program, University of Northern British Columbia 

Chair of Oral Examination

• Dr. Charlotte Norris, School of Environmental Studies, UVic

   

Abstract

Surface erosion of cohesive soils poses significant risks to environmental sustainability and infrastructure stability. The erodibility of such soils is largely governed by the physicochemical properties of both the soil matrix and the surrounding pore fluids. Despite decades of research, the underlying mechanisms linking soil–fluid chemistry to erosion resistance remain insufficiently understood and inconsistently reported. 

This thesis investigates the physicochemical controls on cohesive soil erodibility through an integrated approach combining a comprehensive literature synthesis and targeted laboratory experimentation. The review component compiles and evaluates past studies on the individual / coupled effects of temperature, salinity, and pH on soil erosion behavior, emphasizing their roles in modifying the electric double layer (EDL), soil fabric, and interparticle bonding. The analysis highlights that conflicting conclusions across the literature often stem from inadequate control of chemical variables, incomplete mechanistic interpretation, and a lack of coupled investigations. 

To address these gaps, a series of controlled erosion tests were conducted on kaolinite-based soils using a custom-built Rotating Surface Erosion Apparatus (RSEA) designed with corrosion resistant materials. Nine synthetic pore fluid compositions with systematically varied pH (4–10) and salinity (0–0.5 mol/L NaCl) were prepared to quantify the coupled influence of these factors. Erosion rate–shear stress relationships were established, from which an erosion energy index was developed to characterize soil erodibility. The results demonstrate that both high salinity and pH deviations from neutrality enhance soil structure rearrangement, alter zeta potential, and modify interparticle interactions, leading to measurable changes in erosion resistance. The proposed mechanistic model links these observations to transitions in clay fabric (edge–face to face–face associations) induced by electrochemical effects. 

The thesis provides a unified physicochemical–fabric–erodibility framework that reconciles disparate findings in the literature and elucidates how coupled pH–salinity conditions govern the erosion of cohesive soils. The outcomes contribute to a more consistent understanding of soil fluid interactions and support the development of predictive models for erosion under variable geochemical environments. 

Keywords Cohesive soil, erodibility, pH, salinity, physicochemical interaction, electric double layer, soil fabric