Analysis of Factors and Mechanisms Influencing the Matric Suction and Water-Holding Capacity of Carbonate Saline Soil

Unsaturated saline soils are widely present in engineering, and their matric suction is crucial for engineering design and stability analysis. To explore the factors influencing matric suction characteristics, the filter-paper method was used to measure the matric suction of unsaturated saline soils under different compaction degrees and salt contents. The results show that matric suction decreases with increasing water content, and the change is more obvious in the absorbed film regime (water content = 14–22%). The increase in compaction degrees leads to an increase in matric suction, but the impact is relatively minor in the low suction regime. The increase in salt content indirectly changes the thickness of the bound water film, causing the matric suction to decrease first and then increase; the threshold value of the salt content is 1.2%. In addition, the applicability of traditional soil–water characteristic curve models is limited in saline soils. However, the modified Gardner model considering the bound water content can more accurately describe the soil–water relationship of saline soils. These research findings provide a key foundation for the in-depth comprehension of the engineering properties of saline soils and their effective application in practical engineering.