Publication Date
12-2025
Date of Final Oral Examination (Defense)
10-7-2025
Type of Culminating Activity
Thesis
Degree Title
Master of Science in Geophysics
Department
Geosciences
Supervisory Committee Chair
Qifei Niu, Ph.D.
Supervisory Committee Member
Lee Liberty, M.S.
Supervisory Committee Member
Jennifer Pierce, Ph.D.
Supervisory Committee Member
Bhaskar Chittoori, Ph.D.
Abstract
The Critical Zone (CZ) of Earth is a dynamic region where climate, organisms, relief, parent material, and time (CLORPT) interact to shape the processes that sustain life. The bedrock in the CZ is constantly transformed into regolith as a result of chemical and physical weathering. This creates the porous regolith layer that supports life on Earth. Understanding how weathering alters regolith properties is essential for interpreting subsurface processes such as water retention. Recently, geoelectrical methods have been increasingly used in CZ hydrology to characterize subsurface structure and to monitor water dynamics in CZ. However, to interpret these field geoelectrical data accurately, one needs to know how weathering affects the geophysical properties of CZ materials. This research focuses on how weathering changes basic soil properties in granitic regolith and how those changes affect its hydraulic and electrical properties.
This study collected regolith samples from different depths along a climatic gradient within the Dry Creek Experimental Watershed (DCEW), Idaho. Various laboratory analyses were performed to determine mineralogy, texture, surface area, surface chemistry, hydraulic properties, and electrical properties. The hydraulic and electrical data were modeled using the van Genuchten and Waxman-Smits equations respectively. Model parameters were then correlated with the measured physical and chemical properties of regolith to determine any relations.
The results demonstrate that weathering transforms primary minerals (such as feldspar) into secondary clays and alters basic soil properties such as mineralogy, texture, and surface chemistry. These changes influence hydrological and geophysical properties of the weathered regolith. Soil hydraulic behavior is best captured by the van Genuchten model. According to the results, fitting parameter n̅ (pore-size distribution index/ shape parameter) is controlled by the uniformity coefficient (Cu; R^² = 0.905), indicating that broader grain size distribution gives more gradual water retention curves. Inverse air-entry pressure (α) is best predicted by effective grain size (D10; R^² = 0.946)), and the residual water content (θr) is most strongly associated with clay content (R^² = 0.959). The complex electrical behavior of regolith is captured by the Waxman-Smits model. According to the results, the saturation exponent (n) is linked to Cu (R^² = 0.942). The real surface conductivity (σ′s) and imaginary surface conductivity (σ″s ) are strongly controlled by the cation exchange capacity (CEC; R^² = 0.966 and 0.943, respectively). These results show that surface charge and clay content are the dominant controls on electrical conductivity and polarization. Together, these results show how weathering influences the relationships between basic soil properties and hydraulic and electrical properties of granitic regolith within the CZ.
DOI
https://doi.org/10.18122/td.2461.boisestate
Recommended Citation
Liyanage, Surani, "A Laboratory Investigation of the Dominant Controls on Hydrologic and Electrical Properties of Granitic Regolith" (2025). Boise State University Theses and Dissertations. 2461.
https://doi.org/10.18122/td.2461.boisestate