Abstract: The unfavorable engineering characteristics of saline soil such as salt expansion and solution subsidence have extremely adverse effects on the construction of transportation infrastructure and its safe operation. The mechanism of improving saline soil by adding sodium silicate, cement, lime, fly ash and fiber and the microscopic characteristics of improved soil were investigated via unconfined compression test and SEM-EDS test on the chloride saline soil of subgrade in south Xinjiang. Results manifest that with the 28 d compressive strength as the evaluation standard, the optimal combination in scheme 1 (cement content 8%, lime content 12%, fiber content 0.2%, and fiber length 18 mm, with a salt content of 3%) is suitable for improving medium chloride saline soil; the optimal combination in scheme 2 (fly ash content 20%, lime content 6%, fiber content 0.2%, and fiber length 12 mm, with a salt content of 1%) is suitable for improving weak chlorine saline soil. The improved saline soil modified by the aforementioned two schemes could both retain high compressive strength after reaching stress peak, and the stress-strain curves display strain softening feature with brittle failure. Microstructure and EDS analysis illustrate that the mineral particles of the modified and solidified saline soil are relatively large with sound particle integrity. The cementitious material is composed of flocculent calcium silicate hydrate and acicular ettringite with dense microstructure. The contact mode between particles is mainly face-to-face contact. Compared with those in scheme 2, the improved soil specimen in scheme 1 is of dense internal structure, good internal integrity, and superior strength performance.

Key words: chloride saline soil, orthogonal test, unconfined compressive strength, microscopic characteristics, SEM-EDS test