Abstract
The warm and ice-rich frozen soil (WIRFS) that underlies roadway embankments in permafrost regions exhibit large compression and thaw deformation, which can trigger a series of distresses. Cement and additives were used in this study to improve the compressibility and thaw-settlement properties of WIRFS. We, therefore, selected optimum additives and studied the improvement effect on the frozen soil with 30% water content based on our previous research. Given constant load and variable temperatures, compression coefficients, thaw strains, and water content changes were obtained at temperatures of −1.0 °C, −0.5 °C, and 2.0 °C to evaluate the effect of improvements. A scanning electron microscope (SEM) was then used to observe the microstructure of improved soils and analyze causal mechanisms. Data show that hydration reactions, physical absorptions, cement, and additives formed new structures and changed the phase of water in frozen soil after curing at −1.0 °C for 28 days. This new structure, cemented with soil particles, unfrozen water, and ice, filled in the voids of frozen soil and effectively decreased the WIRFS compression coefficient and thaw strain.
Highlights
Warm and ice-rich frozen soil (WIRFS) is a kind of substrate that has a temperature above−1.5 ◦ C and an ice content above 20% [1], as well as high environmental sensibility, low mechanical strength, large compressibility, and huge thaw settlement [2,3]
Particle size distributions within samples, as well as their physical and chemical properties, are shown in Table 1 and additives selected for evaluation in this study were super absorbent polymer (SAP), ordinary Portland cement (P·O 42.5), geopolymer (GP), anti-freezing agent (AFA), early strength agent (ESA), metakaolin (MK), and three soil stabilizers (i.e., EN-1, an inorganic additive (IA), and Toogood)
We show that unreacted fly ash particles perform as solid spheres because their diameters are distributed from several micrometers to hundreds of micrometers, while calcium silicate hydrates (CSH) gels are cemented onto the surface of partially reacted fly ash particles [25]
Summary
Warm and ice-rich frozen soil (WIRFS) is a kind of substrate that has a temperature above−1.5 ◦ C and an ice content above 20% [1], as well as high environmental sensibility, low mechanical strength, large compressibility, and huge thaw settlement [2,3]. Because of the existence of the WIRFS, permafrost regions have enhanced the occurrence of geological hazards and asymmetrical embankment settlements of roadways [4,5]. These phenomena have affected operational safety and increased the maintenance cost of roadways [6]. Studies on the compressibility and thaw settlement of WIRFS is significant to calculate embankment settlement and analyze deformation characteristics. Ice-rich frozen soil settlement during thawing is relative to dry density and the compression coefficient, based on the calculation model of the total settlement of the embankment that can be constructed [8]. We know that settlement deformation comprises three stages that are interactive and simultaneous, thawing settlement, creep, and settlement caused by freezing and thawing [9,10]
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