Salt crystallization causes a decrease in compressive performance and microstructral damage of lime cured sulfate soil. A series of tests, including unconfined compressive strength test, SEM observation, and EDS test, were conducted on lime stabilized soil with a salt content of 0.3% to 5% to study the relationships between salt content, compressive strength, and microstructure indicators. The results show that: (1) The compressive strength of the soil first increases and then decreases with the increase of salt content, and the strength of stabilized soil with salt content of 1.5% reaches its maximum. (2) When the salt content is less than 1.5%, the shape of soil particles tends to be an ellipse, and the soil structure becomes compact. After the salt content is more than 1.5%, the shape of soil particles tends to be a circle, leading to the instability of the soil structure. (3) For soil with low salt content, some salt particles fill the soil pores and play a role as soil skeleton, improving the strength of the soil. But the salt content is more than 1.5%, and salt swelling plays a dominant role, weakening the structural stability of the soil. Therefore, lime can be used to stabilize the soil with a salt content less than 1.5% to meet the requirements of oil and gas pipeline foundation engineering. Saline soil with a salt content above 1.5% cannot be directly used in engineering, and special research should be conducted.

Generally, synthetic fiber, mineral fiber and plant fiber are added into soil to enhance the strength and deformation resistance of soil. The unconfined compressive test and splitting tensile test of three fiber-lime-soils under freeze-thaw cycle were carried out to study the variation of compressive and tensile properties of soil with freeze-thaw times. The test results showed that the optimum fiber rates of polypropylene fiber-lime-soil, basalt fiber-lime-soil and palm fiber-lime-soil were 0.2%, 0.2%, and 0.4% respectively, whether under freeze-thaw cycle or not. With the increase of freeze-thaw times, the compressive strength and tensile strength of the three fiber-lime-soils demonstrated phased downward trend, and the failure strains of fiber-lime-soil were greater than that of lime-soil. Under freeze-thaw cycle, the compressive strength, tensile strength, and deformation resistance of polypropylene fiber-lime-soil were better than those of basalt fiber-lime-soil and palm fiber-lime-soil. The interface force and the spatial constraint between fibers and soil particles enhanced the freeze-thaw durability of soil. By comparing and analyzing the test results of three types of fiber-lime-soil, it was found that the freeze-thaw resistance of polypropylene fiber-lime-soil was the optimum.