Effect of freezing-thawing cycles on mechanical properties and microscopic mechanisms of loess
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摘要:
青海地处多年冻土地区，属于青藏高原大陆性气候带，冻融循环是路基和地基基础的一种常见破坏因素，为研究冻融循环作用对青海地区实际工程的影响，揭示冻融循环作用对其损害的机理，通过对青海西宁地区原状黄土和重塑黄土进行冻融循环试验、无侧限抗压强度试验和电镜扫描试验，分析不同冻融温度和不同冻融循环次数对原状黄土、重塑黄土无侧限抗压强度和微观结构的影响。结果表明：当黄土经历0～6次冻融循环时，原状黄土和重塑黄土的强度逐渐降低，而8～10次冻融循环后其强度先增大后趋于稳定；原状黄土的强度随冻融温度降低而降低，而重塑黄土的强度随冻融温度降低先增大后减小；从微观角度分析，冻融温度的降低和冻融循环次数的增加，均导致黄土大颗粒逐渐分解为小颗粒，颗粒的排列方式发生改变。
Abstract:Qinghai is located in a permafrost region, which belongs to the continental climate zone of the the Qinghai-Tibet Plateau. At the same time, freezing-thawing cycles are common destructive factors for roadbeds and foundations. In order to examine the effects of freezing-thawing cycles on actual projects in Qinghai and reveal the mechanisms of freezing-thawing cycles on damage of the projects, the freezing-thawing cycle test, unconfined compressive strength test and electron microscope scanning test of the undisturbed loess and remolded loess in the Xining area of Qinghai are conducted to analyze the influence of different freezing-thawing temperatures and different freezing-thawing cycles on the strength and microstructure of the undisturbed loess and remolded loess. The results show that when the loess undergoes 0-6 freezing-thawing cycles, the strength of the undisturbed loess and remolded loess gradually decreases. After 8-10 freezing-thawing cycles, the unconfined compressive strength of the loess first increases and then tends to be basically stable. The strength of the undisturbed loess decreases with the decrease of the freezing and thawing temperature. However, the strength of the remolded loess first increases and then decreases with the decrease of temperature. From a microscopic point of view, the decrease in freezing-thawing temperature and the increase in the number of freezing-thawing cycles both lead to the decomposition of large loess particles into small particles, and the arrangement of the particles has changed. The results are of reference value for actual project construction and construction in the Xining area of Qinghai.
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Key words:
- freezing-thawing cycle /
- loess /
- temperature /
- mechanical properties /
- micromechanism
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表 1 基本物理性质指标
Table 1. Basic physical properties
天然
含水率/%天然密度/
（g·cm−3）最大干密度/
（g·cm−3）最优
含水率/%液限/% 塑限/% 塑性指数 13.1 1.5 1.7 14.2 25.0 13.8 11.1 
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