Abstract: The repeated freeze-thaw cycles with seasonal alternations have an obvious effect on soil structure. To reduce the sensitivity of saline soil to temperature and then use it in engineering, a combined treatment method is proposed, where lime, fly ash and modified polyvinyl alcohol (MPA) are used as solidified materials. Unconfined compressive strength (UCS) and microstructure characterization tests are firstly used to evaluate the solidified effect and obtain the parameters scope of solidified materials. Then the tests of shear strength (cohesion and internal friction angle) and the orthogonal experiment are used to analyze the influence of each factor, and then obtained the optimal combination of solidified parameters. The results indicate that the combination of lime, fly ash and MPA can improve the strength of saline soil. After combined treatment, the UCS is 1 130.25 kPa, which is 5.18 times than that of saline soil (218 kPa). The strength of combined solidified saline soil meets the requirements of engineering specification (JTG 3430－2020). The stable value of UCS of combined solidified saline soil under freeze-thaw cycles is 700 kPa. The fluctuation is about 5% after three freeze-thaw cycles. The cohesion and the internal friction angle of combined solidified saline under the most appropriate ratio can be 208.2 kPa and 38.56°, respectively after three freezing-thawing cycles. The sensitivity ranking of the factors is as follows: curing time, lime content, MPA content, dry density, salt content, and times of freeze-thaw cycles. With an increase in lime, fly ash and MPA content, the strength of combined solidified saline soil increases and then tends to become stable. The optimization of solidification parameters can effectively weaken the influence of freeze-thaw on coastal saline soil. Based on tests results of compressive strength and shear strength, it can be concluded that the optimal combination of solidified parameters is 14% of lime, 30% of fly ash, 1% of MPA, 28 days of curing time, and a dry density of 1.65 g/cm3.

Key words: mechanical property, freeze-thaw performance, combined solidified method, compressive strength, shear strength, microstructure, saline soil