Characterization of Mechanical and Thermal Properties of Highly-Cemented Edmonton Clay Subjected to Freezing/Thawing

Abstract

Deep soil mixing (DSM) with cement has been utilized to enhance soft ground and stabilize problematic soils worldwide and has become more commonly used in cold regions, which requires a thorough understanding of the behavior of DSM-treated natural soils (soilcrete) exposed to severe cold environments. Previous research on soilcrete was concentrated on determining the performance of lightly-cemented soilcrete under temperate conditions. Therefore, the present thesis is aimed at investigating the performance of soilcrete with a high cement content (over 20%) under the freezing/thawing (F/T) cycles, including physical, mechanical, hydraulic, thermal, and microscopic properties. In the present study, cylindrical soilcrete specimens were prepared in the laboratory by mixing Edmonton clay with high contents of ordinary Portland cement. The uniaxial compressive and tensile behavior of soilcrete with/without F/T cycles were examined with unconfined compression strength (UCS) and tensile tests on specimens cured for 1 to 300 days after 1 to 20 F/T cycles at freezing temperatures from ¬−2 to ¬−20 °C. The results showed that the compressive and tensile strength of soilcrete increased with curing age and decreased significantly with F/T cycles. Additionally, the lower temperature caused more severe damage to the samples than the number of cycles. The mechanical properties of soilcrete in isotropically consolidated undrained (CIU) triaxial tests were determined and the permeability was measured by conducting tests on soilcrete specimens with a cement content of 22%. Meanwhile, the damage of F/T cycles on the solids phase alone was examined with UCS tests on dry soilcrete samples. Results of CIU tests indicated that the cohesion of soilcrete decreased with the declining freezing temperature, while the friction angle remained nearly unchanged after F/T cycles. In addition, the permeability of soilcrete showed a significant increase after F/T cycles and the impact of lower freezing temperatures on permeability was more noticeable than that due to the number of cycles. UCS results of dry samples showed that the damage from F/T cycles was negligible, probably confirming that F/T damage on soilcrete was primarily due to the water phase of specimens. The thermal conductivity of soilcrete has seldom been studied in the literature. The thermal conductivity of soilcrete under a cold environment was estimated using a temperature control system, which mimics a radial heat transfer flow and uses dry sand with a known thermal conductivity as the medium. Temperature distribution in soilcrete and sand confirmed that a steady state was achieved. The thermal conductivity of soilcrete at various freezing temperatures was calculated based on the temperature distribution. Thermal conductivities of soilcrete obtained in the present study were in line with those values determined using empirical equations in the literature and back-analyzed from finite element simulations. The microstructure of soilcrete after F/T cycles at different freezing temperatures was investigated using the X-ray computed tomography scanning method. Results showed that the volumetric cavity ratio of the soilcrete changed significantly after the F/T cycle and increased with the declining temperature. The cavity was divided into planar cracks and bulky holes based on their geometry. The volumetric distribution of planar cracks was illustrated and the equivalent diameter distribution of bulky holes varied with temperature