Impact of Freeze-Thaw Cycles on Porosity Change in Shalles and Its Implications on Erodibility

Cut slopes for transportation assets can expose near-surface shales, which are highly degradable materials. Initially, these cuts appear stable, but the material can quickly weather into loose sediment. Predicting this degradation is essential because intact shale is a stable, non-erodible geomaterial, whereas weathered sediment is highly erodible and leads to sediment transport that must be managed. While studies have highlighted the importance of porosity changes in relation to shale erosion, the relationship between weathering, porosity evolution, and fracturing in fine-grained sedimentary rocks like shale has not been extensively studied, despite extensive research on soil erosion. The objective of this thesis is to understand how freeze-thaw cycles affect the hydraulic conductivity and porosity of shales over time. This research focuses on predicting degradation due to freeze-thaw cycles, which alter porosity, reduce strength, and increase erosion susceptibility. Shale samples were collected in Shelby tubes from five cut slopes in Kansas. The samples were saturated and directly tested in a custom falling head hydraulic conductivity test. They were subjected to freeze-thaw cycles ranging from -10°C to 40°C, replicating Kansas soil temperatures, until the specimen mass stabilized. This process of saturation, hydraulic conductivity testing, and freeze-thaw cycling was repeated until the samples sustained damage or detached from the Shelby tubes. Using the Kozeny-Carman Equation, porosity was determined from the hydraulic conductivity data. A prediction model was developed based on these results to estimate the number of cycles required for intact shale to reach the porosity of weathered rock, which was then validated with additional samples. The results showed that hydraulic conductivity and porosity increased with freeze-thaw cycling for all samples. The prediction model identifies that two sites will degrade within four years, one within years, and one 13 years. Two validation tests conducted to observe the accuracy of the prediction model indicate an error margin of less than 1% for the predicted porosity for a specified number of cycles through 50 cycles. The measured increase in porosity due to freeze-thaw cycles supports the observation of rapid shale deterioration and increased erodibility, highlighting the need for protective strategies during construction and maintenance to ensure stability. Understanding these dynamics is essential for predicting erosion and managing environmental and infrastructure safety issues related to sediment displacement and debris accumulation.

Name thesis:degree_name

Master of Science

Level thesis:degree_level

Masters

Discipline thesis:degree_discipline

Civil Engineering

Grantor

Texas State University

Year dc:date.issued

2024

Author dc:creator

• Barman, Konica

Advisor dc:contributor.advisor

• Kulesza, Stacey

Committee members dc:contributor.committeemember

• Espinoza Chavez, Wilson F.
• Wang, Feng

• hydraulic conductivity
• porosity
• freeze-thaw cycles
• shale degradation

Language dc:language.iso

en

Handle dc:identifier.uri

https://hdl.handle.net/10877/19282

OAI identifier oai:identifier

oai:digital.library.txst.edu:10877/19282