Theses and Dissertations

Issuing Body

Mississippi State University


Vahedifard, Farshid

Committee Member

Ramirez-Avila, John J.

Committee Member

Taylor, Oliver-Denzil S.

Committee Member

Peters, John F.

Date of Degree


Document Type

Dissertation - Open Access


Civil Engineering

Degree Name

Doctor of Philosophy (Ph.D)


James Worth Bagley College of Engineering


Department of Civil and Environmental Engineering


Wildfires result in altered landscape as well as altered soil properties. Wildfires result in conditions that are more susceptible to geotechnical hazards introducing a potential for cascading events in the surrounding area. Shallow landslides are common geohazards that result in a post-wildfire landscape. With an ever-increasing trend in wildfires, the need to better understand the impact wildfire-altered soil properties play on shallow slope instability is critical to evaluating risks to existing or planned development, mitigation of potentially hazardous conditions, prioritization of post-wildfire planning, and post-wildfire response preparation. The primary objective of this study is to provide a comprehensive overview of wildfire-altered geotechnical soil properties and their impact on rainfall-triggered landslides. For this purpose, laboratory and field testing has been performed on soil samples collected from four wildfire areas in California. In-situ hydraulic conductivity tests were performed on both burned and unburned soil. Soil samples collected from burned and unburned areas were tested in for index properties, shear strength, organic content, and pH. Results show that the mean angle of internal friction was reduced in burned soil samples for all study areas, the mean pH, organic content, and hydraulic conductivity were all greater in burned soils in all study areas, and cohesion was found to have contradicting trajectories. Resulting soil properties have been used to compare the factors of safety for representative unburned and burned slopes using a finite element seepage analysis and limit equilibrium slope stability analysis. The unburned and burn soil sample results are used to determine relative factors of safety for slope stability at each of the four wildfire areas. Peak historic and predicted precipitation have been used to further evaluate the relative factors of safety for pre and post-wildfire slope stability conditions. The comparative slope stability analysis has been used to provide a quantitative comparison of the role altered soil properties play on the potential for slope instability. Through this study, it is apparent that although soil properties are altered by wildfire, the impact altered soil properties have on the subsequent slope instability is much less than that of other contributing factors, including precipitation and root support.