During winter construction of earthworks such as earth dams and embankments, the structural properties of the soil may deteriorate due to freeze-thaw cycles. A new measure to combat freeze-thaw damage, incorporating phase change materials (PCMs) into the soil to regulate temperature, has been verified and applied in roadbed and pavement engineering. However, the law of deterioration from freeze-thaw cycles for this novel construction material is not clear yet. This study investigated the characteristics and mechanism of deterioration of clay mixed with paraffin-based PCM (PPCM-clay) through freezing and thawing using freeze-thaw tests, unconfined compression tests, permeability tests, and macro-micro structural analysis. The results show that the freeze-thaw resistance of PPCM-clay is better than that of pure soil. The amount of PPCM added is proportional to the effect of inhibiting soil strength and permeability degradation. Under the same number of freeze-thaw cycles, the compressive strength of PPCM-clay is greater than that of pure soil. Micropore expansion and frost heave are also not significant in PPCM-clay. This indicates that the low initial water content, relatively large porosity, thermal hysteresis, frost contraction, hydrophobicity, and high viscosity of PPCMs are the main reasons for the improvement in PPCM-clay freeze-thaw resistance. These findings provide a theoretical basis for the potential application of PPCM-clay as a dam or embankment material for weakening soil frost damage in winter construction in cold regions.

Compacted loess is widely used in construction and road engineering in the Loess Plateau region. It inevitably undergoes vertical deformation and desiccation-induced cracking due to environmental effects. This study investigates the deformation and cracking characteristics of compacted loess under vertical pressure during desiccation. Samples with initial water contents ranging from 5% to saturation are prepared for desiccation under vertical stresses of 0-100 kPa. Changes in resistivity are simultaneously monitored during desiccation. After desiccation, the microstructural characteristics of the soil are examined using X-ray computed tomography (CT), mercury intrusion porosimetry (MIP), and scanning electron microscopy (SEM) techniques. The effects of initial water content and vertical pressure on vertical strain, drying cracks, and electrical resistivity of compacted loess are analyzed. The results indicated that high vertical pressure and water content lead to significant compressive and desiccated deformation of compacted loess, which is reflected in the microstructure by a smaller pore size distribution (PSD). Lower initial water content and higher vertical load are more effective in suppressing cracking during the desiccation of compacted loess. The surface crack ratio (Rsc) of compacted loess is reduced by 99.54% as pressure increases from 0 to 100 kPa and water content decreases from saturation to 5%. The directions of cracks in loess during desiccation and the microstructural changes caused by deformation are effectively characterized by resistivity measurements. This study explores the variations in mechanical properties during desiccation of compacted loess and provides a theoretical foundation to use resistivity for characterization.

Shanghai soft clay is a typical marine clay with specific structural characteristics. The tunnel and overlying soft clay may undergo repeated surface surcharge loading, such as the temporary soil stacking. Assessing the extent of structured soft clay deformation and tunnel displacement caused by repeated surface surcharge loading is of great significance for evaluating of the safety of ground structures and underground tunnels. In this study, the effects of repeated surface surcharge loading on the soil and tunnel displacement were numerically investigated. The finite element code DBLEAVES with an elasto-plastic constitutive model (Shanghai model) that describes the mechanical properties and structural characteristics of natural clay was used to simulate the soil response. The parameters of the constitutive model were obtained through geotechnical testing. The effects of the soil structural characteristics, seepage conditions, and loading conditions on the soil response and tunnel displacement were analyzed. The numerical results show that the maximum excess pore pressure of clay decreased as the number of loading cycles increased. The effects of the structural characteristics cause greater displacement, whereas the effects of the degradation parameters of the structure are more significant than the initial degree of the structure. The differences in the vertical displacement of the tunnel and overlying soils owing to the structural characteristics become apparent with an increase in surface surcharge loading. However, the effects of structural characteristics become less significant as the depth increases. The seepage conditions and loading method primarily affect the build-up of excess pore pressure and the development of effective stress paths. For soils inside the surcharge area, a flexible surcharge produces a greater vertical displacement than a rigid surcharge. As the burial depth increased, the effects of the seepage conditions and loading method showed a declining tendency.