Unsaturated Hydraulic Conductivity Variation of Expansive Yazoo Clay with Wet-Dry Cycles

Abstract

Expansive soils are subjected to shrink-swell behavior with moisture variation in Mississippi, United States. With successive moisture and temperature variations over the seasons, the hydraulic conductivity of expansive soil is subjected to change because of the development of shrinkage cracks, which can be as large as as 1.2 cm wide and 1.5 m deep in the field, affecting the vertical hydraulic conductivity (Kv), whereas the horizontal hydraulic conductivity (Kh) remains fairly constant. The current study intends to investigate the hydraulic conductivity of highly expansive Yazoo clay at different wet-dry cycles. To observe the changes in the hydraulic conductivity with different wet-dry cycles in the laboratory, an instantaneous profile method to measure the permeability was utilized. Compacted Yazoo clay samples at different initial moisture content instrumented with moisture sensors at different depths to monitor changes in the moisture content were investigated. The samples were subjected to one, two, and three numbers (1N, 2N, and 3N) of wetting and drying cycles. For the drying process, testing chambers are kept in a controlled high-temperature booth of about 37°C simulating high summer temperatures in Mississippi. After the end of the wet-dry cycles, the test is performed to investigate the changes in the hydraulic conductivity of soil with the presence of shrinkage cracks. The hydraulic conductivity of highly plastic clay is very low at a fully compacted state and was observed to be (1.0×10-8 cm/s) at the 1N wetting phase. However, with an increment in the wet-dry cycles, the Kv of Yazoo clay increases (3.70×10-4 cm/s) after the sample is exposed to three wet-dry cycles. Even though the changes in the Kv of highly plastic clay define the infiltration behavior, which mostly controls the slope failure and pavement distress, consideration of the climatic loads is ignored in the design phase of the highway embankment and levees. By inclusion of the climatic variation, and evaluating the performance, the design life and resilience of the structures can be significantly increased