Experimental investigation into the salinity effect on the physicomechanical properties of carbonate saline soil

Abstract

For engineering structures with saline soil as a filling material, such as channel slope, road subgrade, etc., the rich soluble salt in the soil is an important potential factor affecting their safety performance. This study examines the Atterberg limits, shear strength, and compressibility of carbonate saline soil samples with different NaHCO3 contents in Northeast China. The mechanism underlying the influence of salt content on soil macroscopic properties was investigated based on a volumetric flask test, a mercury intrusion porosimetry (MIP) test, and a scanning electron microscopic (SEM) test. The results demonstrated that when NaHCO3 contents were lower than the threshold value of 1.5%, the bound water film adsorbed on the surface of clay particles thickened continuously, and correspondingly, the Atterberg limits and plasticity index increased rapidly as the increase of sodium ion content. Meanwhile, the bonding force between particles was weakened, the dispersion of large aggregates was enhanced, and the soil structure became looser. Macroscopically, the compressibility increased and the shear strength (mainly cohesion) decreased by 28.64%. However, when the NaHCO3 content exceeded the threshold value of 1.5%, the salt gradually approached solubility and filled the pores between particles in the form of crystals, resulting in a decrease in soil porosity. The cementation effect generated by salt crystals increased the bonding force between soil particles, leading to a decrease in plasticity index and an improvement in soil mechanical properties. Moreover, this work provides valuable suggestions and theoretical guidance for the scientific utilization of carbonate saline soil in backfill engineering projects.