Abstract
Undisturbed loess is affected by external environmental disturbances, such as wetting and freeze-thaw cycles, which cause microstructural changes that have an important impact on the structural strength of the loess. These changes in turn affect the stability of structures such as embankments, slopes, and guards. This article takes the Q3 undisturbed loess in Lintong District, Xi’an, as an example. The effects of wetting and freeze-thaw cycles on the loess expansion ratio and pore structure were studied by wetting tests, freeze-thaw cycle tests, and scanning electron microscopy (SEM). The changes in the compression index and compression modulus were studied by a confined compression test. The loess e-lgp compression curve was obtained according to the confined compression test, and the newly defined concepts of the loess structural strength, residual structural strength, and structural strength damage variable, in addition to the e-lgp compression curve, were combined with the experimental data to calculate the damage value generated by the disturbance during the sampling and preparation of loess. The deterioration of the structural strength and damage variable of loess was analyzed. Based on the microscopic statistical damage theory and Weibull distribution, the model used the volume expansion ratio as a variable to establish a statistical damage model under wetting and freeze-thaw cycles. Finally, on the basis of the test, the model parameters were determined. The models were verified by taking loess from a foundation pit in the northern suburbs of Xi’an and were in good agreement with the results of the test. Ultimately, the models have good practicability and can provide guidance for engineering design and construction.
Highlights
Loess is a porous, weakly cemented Quaternary sediment and is mostly distributed [1, 2] in arid and semiarid regions in Asia, Europe, North America, and South America
(3) Figures 18(c)–18(f ) show that when wP < w ≤ wL, the compression index Cc increases greatly with the number of freeze-thaw cycles, and the compression modulus Es changes less, which indicates that the volume increase due to the water phase change has a greater influence on the spatial arrangement of the microstructure, and the structural strength is reduced at a faster rate
Soil and water action can reduce the bonding force of the cementing material between the loess microparticles or the microparticle aggregates, and the lubricating property of water significantly reduces the friction between the microparticles or the microparticle aggregates, reducing the structural strength of the loess
Summary
Weakly cemented Quaternary sediment and is mostly distributed [1, 2] in arid and semiarid regions in Asia, Europe, North America, and South America. (2) Figures 18(a) and 18(b) show that when w ≤ wP, the compression index Cc and the compression modulus Es change little as the number of freeze-thaw cycles increases, which indicates that the volume increase due to the water phase change has little effect on the structural strength of the loess. (3) Figures 18(c)–18(f ) show that when wP < w ≤ wL, the compression index Cc increases greatly with the number of freeze-thaw cycles, and the compression modulus Es changes less, which indicates that the volume increase due to the water phase change has a greater influence on the spatial arrangement of the microstructure, and the structural strength is reduced at a faster rate. When w > wL, the compression index Cc and the compression modulus Es both change slowly with the number of freeze-thaw cycles, which indicates that the loess has rheological properties and that the microstructure of the loess is self-healing due to the rheological action after the solid water melts; the rate of structural strength reduction is slowed down
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