An experimental study of salt expansion in sodium saline soils under transient conditions

Abstract

Salt expansion in sulfate saline soils that are widely distributed in northwestern China causes serious infrastructural damages under low-temperature conditions. However, the mechanism of salt expansion under low temperatures is not clear. In this study, we conducted a series of cooling experiments combined with salt crystallization to study this mechanism, and employed an ionic model to calculate the supersaturation ratio of the solution. During the experiments, the strength and the process of salt expansion were examined under different cooling rates and various crystal morphologies. The relationship between temperature and supersaturation ratio under transient conditions was also considered. Results indicate that the initial supersaturation ratio of a sodium sulfate solution is closely related to environmental conditions, and that this ratio decreases with slowing the cooling rates and stabilizing the crystal forms. Higher initial supersaturation ratios lead to an increased non-steady-state zone, resulting in less salt expansion. On the other hand, chloride ion content has a distinct influence on the crystallization supersaturation ratio of the sodium sulfate solution, and higher chloride ion content can inhibit salt expansion in sodium saline soils. These findings help explain salt expansion mechanisms in complex conditions such as seasonally frozen soils, and thus help search for improved methods of preventing salt expansion in sulfate saline soils.

Experimental Study on Influence of Vaporous Water on Salt Expansion of Sulfate Saline Soil

“…In addition, standard sand with uniform gradation distribution is used to prepare dry sulfate saline soil samples for the tests in this paper, while salt expansion of sulfate saline soil is also significantly affected by the particle size distribution, density, porosity, and overlying load of the soil sample [5, 10-14, 20, 26]. e effects of these factors on salt expansion are more complicated [10,13,14], which need to be verified by further research.…”

“…Wu et al [12] and Wan et al [13] investigated the salt expansion characteristics of sulfate saline soil under variable water content. Wan et al [14,15] studied the precipitation law of sodium sulfate decahydrate crystals in sulfate saline soil during the cooling process and established the relationship between varying water content and temperature reduction. Chen et al [16] and Lv et al [17] experimentally studied the reduction law of salt expansion of sulfate saline soil under the action of insulating layer and soilbag.…”

The Equilibrium Time and Salt Expansion Characteristic of Sulfate Saline Soil upon Cooling

“…When the water content and the degree of compaction are under the same level, the salt expansion rate of the Qinghai silty clay shows an increasing tendency with the decrease of the cooling rate. Wan et al [8] found that the salt expansion rate of sulfate saline soil increased with a reduced cooling rate through the one-dimensional salt expansion test under closed conditions. As the cooling rate decreases, the water and salt migration behavior become more distinct.…”

“…e salt crystallization behavior is driven by the temperature difference between daytime and nighttime, and such dissolution effect may easily cause engineering diseases in the continuous salt swelling-collapse process. To better illustrate the temperature effect on the salt expansion process, Lai et al [7] and Wan et al [8,9] conducted salt expansion experiments with different cooling rates. In conclusion, with an increased initial concentration of sulfate content, the cooling rate is slowed down, followed by decreased maximum supersaturation rate, increased salt crystallization rate, and higher salt expansion rate.…”

“…e stabilization time is dependent on the soil size and the cooling pattern [20]. Previous studies [8,33] set each testing stage (with a change of temperature level) as lasting from 2 to 8 hours. e salt swelling development is insufficient when the stabilization time is short.…”