Abstract
The frost heave and thaw settlement caused by freeze-thaw cycles will seriously affect the engineering properties of soil. This paper attempts to comparatively investigate the deterioration effect of freeze-thaw cycles on the mechanical properties of compacted clay in closed and open systems. The specimens were frozen and thawed from the top to bottom in two systems. The moisture contents and deformations after freeze-thaw cycles were measured. Mechanical parameters of soil were examined through triaxial compression tests. Results show that the moisture content and deformation of soil change evidently with the increase of freeze-thaw cycles in the open system, while these parameters in the closed system change little. In the open system, the attenuation rate of failure strength, elastic modulus, and angle of internal friction of soil subjected to 7 freeze-thaw cycles are all about 2 times as large as that in the closed system and the attenuation rate of cohesion is even 4 times of that in the closed system. These differences reveal that the deterioration effect of freeze-thaw cycles on soil strength is aggravated after water supply. These findings indicate that soil structure damage and moisture content increase is the dominant factor affecting engineering properties of the soil in the open system.
Highlights
When the soil completely freezes in situ, the volume of free water in the voids increases by 9%, which is very common in coarse-grained soil, such as sand
For the clayey soil, when the freezing rate is low, especially when there is an external source of water supply, the migration and aggregation of unfrozen water to the frozen front under the driving of cryosuction [1] lead to the formation of the segregated ice, that is, the ice lens, resulting in the frost heave of the soil [2]
E study on the effect of freeze-thaw cycles on the mechanical properties of soil generally adopts two kinds of test methods. e one is the freeze-thaw cycles test in the closed system where no outer water is available during the freezing process, and the other is in the open system where outer water is supplied from the bottom of the sample during the freezing process [8]
Summary
When the soil completely freezes in situ, the volume of free water in the voids increases by 9%, which is very common in coarse-grained soil, such as sand. Referring to the viewpoint of Wong and Haug [8] that the development rate of frost depth is greater than that of moisture migration in soil, numerous authors have studied the influence of freeze-thaw cycles on the mechanical properties of soil under the closed system [9,10,11,12]. Considerable studies have been carried out on the deformation characteristic properties (frost heave and thaw settlement) and water migration property of soils during freeze-thaw processes [16, 17]. Erefore, it is necessary to study the variation of mechanical properties of soil after freeze-thaw cycles under the open system when there is water supply during freezing. Erefore, it is inevitable to study the microstructure changes of soil in the investigation on mechanical properties of clay under freezethaw cycles. The unconsolidated undrained triaxial compression tests on specimens subjected to freeze-thaw cycles were carried out, and typical specimens of the closed and open system were selected for SEM tests, respectively
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