Effect of Freeze-Thaw Cycles on Triaxial Strength Property Damage to Cement Improved Aeolian Sand (CIAS)

Investigating the strength, hydraulic conductivity, and durability of the CSG (cemented sand-gravel) check dams: a case study in Iran

This paper aims to find a proper admixture of the cemented sand-gravel (CSG) material for constructing a hardfill embankment located in cold weather. To this end, the compaction, strength, permeability of the cemented sand-gravel mixtures with cement contents of 5, 7.5, 10, and 12.5% are experimentally studied. Besides, the freeze–thaw durability of native grains of the soil and stabilizing soil is examined. According to the test results, even though the compaction specifications of all mixtures do not considerably depend on the cement content, however the cement content in the mixture significantly influences the compressive strength, stiffness, and permeability of mixtures. The soil aggregates inherently have high water absorption and are thus severely fractured after 50 cycles of freeze–thaw. After stabilizing the soil grains with cement, the freeze–thaw durability of the cemented soil mixture is considerably improved, and the weight loss of all mixtures becomes less than 5% after 12 cycles of freeze–thaw. However, the freeze–thaw cycles reduce the mixture strength up to 40% in comparison with the intact mixture. The analysis of scanning electron microscope images implies that four factors including disintegration of the calcium-silicate-hydration complex, imposing new porosity, releasing interlayered water, and establishing the secondary ettringite are the main reasons for strength reduction of the cemented sand-gravel mixtures after encountering the freeze–thaw cycles which have not been observed in the previous researches.

Model Test Study on Stability Factors of Expansive Soil Slopes with Different Initial Slope Ratios under Freeze-Thaw Conditions

Expansive soil is widely distributed in seasonally frozen areas worldwide. Due to the special expansion and shrinkage characteristics of expansive soil related to water content, there are potential engineering disasters in the subgrade and slope engineering. To investigate the physical and mechanical changes within the expansive soil slope, four freeze-thaw cycles tests were performed on expansive soil slope models in an environmental chamber with slope ratios 1:1.5, 1:1 and 1:0.5. Nuclear magnetic resonance (NMR) technology is used to explain the pore changes in expansive soil during freezing and thawing. Model tests were carried out to monitor the changes in cracks, moisture content, temperature, displacement and soil pressure of the slope model. The results show an increase in the slope ratio may give rise to more intense temperature changes, promote the development of cracks in the model, and increase the temperature gradient and moisture migration rate during freezing and thawing. Following freeze-thaw cycling, the soil structure is destroyed and reassembled, and the soil pressure decreases as the slope ratio increases. Combined with the displacement of slope model and NMR test results, the slope can maintain a stable state after multiple freezing–thawing cycles under a specific moisture content ωs.