Abstract Thermal cycles can remarkably alter the geological and resistance properties of soil beneath structures. This research examined the effect of simultaneous use of glass fiber and nano-SiO2 on strength properties of low plasticity clay (CL) under various thermal cycles. The contents of glass fiber and nano-SiO2 were chosen 1.5%, 2.5%, 3.5% and 0.5%, 1.0%, 1.5% of the soil dry weight, respectively. The strength properties of natural soil and treated clay were estimated via unconfined compression and direct shear tests. Further, the images of scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) tests were used to assess the microstructure of soil affected by freeze and thaw periods. The obtained results indicated that different mixtures of nano-SiO2 and glass fiber can be employed as effective additives to reduce the negative impacts of thermal cycles. The mixture of 1.0% nano-SiO2 and 2.5% glass fiber with clay was found as an optimum mixture content, causing elevation of unconfined compressive strength (UCS) from 0.717 MPa to 1.381 MPa even after 12 thermal cycles. The combined impact of nano-SiO2 and glass fiber on the internal friction angle was greater than its effect on the cohesion of the samples. On the other hand, the cohesion and internal friction angle of the samples treated with 1.0% nano-SiO2 and 2.5% glass fiber were obtained 1.36 and 2.47 times of the natural clay, respectively. Microstructural evaluation through SEM images and BET analyses showed that thermal cycles led to an increase in the micro-voids of clay structure and separated clay minerals from each other. Observation of SEM images reflected the fact that thermal stresses due to freeze and thaw periods caused whiskers' growth from nano-SiO2 surfaces. The whiskers and glass fiber lead to modify strength properties and structure of clayey soil by creating filamentary networks on nano and macro scales, respectively.

中文翻译：

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热循环对纳米处理黏土微观结构和功能特性的影响

摘要 热循环可以显着改变结构下土壤的地质和阻力特性。本研究考察了同时使用玻璃纤维和纳米 SiO2 对不同热循环下低塑性粘土 (CL) 强度性能的影响。玻璃纤维和纳米SiO2的含量分别选择为土壤干重的1.5%、2.5%、3.5%和0.5%、1.0%、1.5%。天然土壤和处理过的粘土的强度特性通过无侧限压缩和直剪试验进行评估。此外，扫描电子显微镜 (SEM) 和 Brunauer-Emmett-Teller (BET) 测试的图像用于评估受冻融期影响的土壤的微观结构。所得结果表明，纳米SiO2和玻璃纤维的不同混合物可用作有效添加剂，以减少热循环的负面影响。发现 1.0% 纳米 SiO2 和 2.5% 玻璃纤维与粘土的混合物是最佳混合物含量，即使经过 12 次热循环，无侧限抗压强度 (UCS) 从 0.717 MPa 提高到 1.381 MPa。纳米SiO2和玻璃纤维对内摩擦角的综合影响大于其对样品内聚力的影响。另一方面，用1.0%纳米SiO2和2.5%玻璃纤维处理的样品的内聚力和内摩擦角分别是天然粘土的1.36和2.47倍。通过 SEM 图像和 BET 分析进行的微观结构评估表明，热循环导致粘土结构的微空隙增加，并使粘土矿物彼此分离。SEM 图像的观察反映了这样一个事实，即由于冻结和解冻期引起的热应力导致晶须从纳米 SiO2 表面生长。晶须和玻璃纤维分别通过在纳米和宏观尺度上形成丝状网络来改变粘土的强度特性和结构。