Effects of thermal cycles on microstructural and functional properties of nano treated clayey soil

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. •Mixing glass fiber and nano-SiO2 lead to modify strength reduction by thermal cycles.•Thermal stresses cause whiskers to grow from the nano-material surfaces.•Whiskers improve the strength properties of clay in the nano scale filamentary.•Glass fiber modify the soil resistance in the macro scale filamentary network.•Impact of nano-fiber on soil friction angle was greater than its effect on cohesion.