Abstract
To explore the mechanism of the microstructural change in salinized soil under freeze-thaw cycles and the strength characteristics of subgrade salinized soil improved by fly ash, an unconfined compressive test, a triaxial shear test, and a scanning electron microscopy test were carried out using salinized soil samples with different fly ash contents along the Suihua to Daqing expressway in China. The results showed that after several freeze-thaw cycles, the unconfined compressive strength, triaxial shear strength, cohesion, and internal friction angle of saline soil showed a decreasing trend. With an increase in the fly ash content, the internal friction angle, cohesion, unconfined compressive strength, and shear strength of the improved saline soil first increased and then decreased. When the fly ash content was 15%, the mechanical indexes, such as cohesion and the internal friction angle, reached the maximum value. Microscopic test results showed that the freeze-thaw cycle will lead to an increase in the proportion of pores and cracks, an increase in the average pore size, and a loosening of the soil structure. The addition of fly ash can fill the soil pores, improve the microstructure of the soil, increase the cohesive force of the soil particles, and improve the overall strength of the soil. Fly ash (15%) can be added to subgrade soil in the process of subgrade construction in the Suihua-Daqing expressway area to improve the shear strength and the resistance to freezing and thawing cycles. These research results are conducive to promoting the comprehensive utilization of fly ash, improving the utilization rate of resources, and promoting sustainable development, thus providing a reference for the design and construction of saline soil roadbed engineering in seasonal frozen areas and the development and construction of saline land belts in seasonal and winter areas.
Highlights
Saline and alkaline soil, as well as the soil following salinization and alkalization, are referred to as saline soil [1,2]
We studied the suitable use of fly ash-modified sulfuric saline soil for roads in cold regions
We found that the strength characteristics of subgrade salinized soil improved by fly ash, and the shear strength, cohesion, and internal friction angle of soil with 15%
Summary
As well as the soil following salinization and alkalization, are referred to as saline soil [1,2]. Due to the large amount of salt in pore water, the structural and strength changes of salinized soil in seasonal permafrost regions are more complex than the changes in the strength and structure of saline soil in non-saline soil [3]. The mechanical properties of saline soil in seasonal permafrost areas are usually poor. If this material is directly used as a basic filling material, a variety of engineering problems may occur [4], such as road grouting, melting settlement, subgrade settlement, and slope stability reduction. To maintain the sustainability of engineering construction in seasonal frozen soil areas and to improve the durability of engineering in these areas, it is of great engineering significance to study the influence of the freeze-thaw cycle on the strength characteristics of saline soil and to improve the properties of saline soil
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