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Water-Salt Migration and Deformation Characteristics of Saline Soil under Different Replenishment Conditions
YANG Bao-cun, JIANG Jian-bing, YANG Xiao-song, LI Bo-yi
Journal of Changjiang River Scientific Research Institute ›› 2025, Vol. 42 ›› Issue (8) : 118-127.
PDF(8089 KB)
PDF(8089 KB)
Water-Salt Migration and Deformation Characteristics of Saline Soil under Different Replenishment Conditions
[Objective] This study aims to investigate the water-salt migration and deformation characteristics of desert saline soil in southern Xinjiang under the combined effects of water-salt replenishment conditions and salt-freeze-thaw cycles. [Methods] According to the types of saline soil and the distribution characteristics of groundwater and salt in the Aral region of southern Xinjiang Autonomous Prefecture, we selected silty sand as the research subject and prepared synthetic sulfate saline soil specimens to conduct cyclic salt-freeze-thaw experiments under two different salt replenishment conditions to simulate secondary soil salinization, namely, groundwater (saline solution) replenishment and engineering replacement (underlying saline soil) replenishment. The water-salt migration features, phase changes, and deformation characteristics of silty sulfate saline soil under the two conditions were analyzed. [Results] Under saline solution replenishment condition, as the concentration of the replenishment solution increased, the migration height of water and salt decreased. The soil deformation characteristics exhibited initial salt-induced swelling followed by settlement, with the maximum salt-induced swelling deformation of 0.21 mm occurring at a 5% solution concentration. Under saline soil replenishment condition, as the sodium sulfate content in the soil increased, the reduction in water and salt content in the lower layer increased, and the soil deformation was characterized by settlement. The maximum settlement deformation of -1.37 mm occurred at a saline soil content of 1%. [Conclusion] Compared to saline solution replenishment, saline soil replenishment results in greater thermal sensitivity of the soil. Under saline solution replenishment condition, the migration of water and salt in soil pores and the trends of deformation and failure occur more rapidly than those under saline soil replenishment condition. Therefore, replacing the sulfate saline soil foundation with an overlying layer of salt-free silty sand can suppress the sulfate-induced frost heave. However, the thickness of the salt-free silty sand layer should exceed the critical depth of thermal influence. In engineering practice, when silty sand—a soil type prone to settlement deformation—is used as an overlying replacement layer to suppress salt-induced frost heave deformation of sulfate saline soil, attention should be paid to particle gradation and compaction of replacement soil, and the implementation of salt-blocking and drainage measures. This research provides a reference for the engineering prevention and control of secondary soil salinization in southern Xinjiang.
silty sulfate soil / freeze-thaw cycle / water and salt migration / deformation characteristics / Southern Xinjiang
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The regularities of water and salt migration in sulfate saline soil as well as their impacts on the frost heave of soil were investigated via indoor soil column test. The changes in moisture content, electrical conductivity, temperature, and displacement during the freeze-thaw cycles were measured by teros-12 and displacement meter. The experimental results demonstrated that in the freezing process from top to bottom, the bottom water moved toward the freezing front, driving the salt accumulating upwards. Meanwhile, the cycles of temperature rising and falling generated a notable hysteresis effect on volumetric moisture content and electrical conductivity of soil. The soil swelled during freezing, and the vertical deformation can be divided into three stages: the adjustment stage caused by the formation of mirabilite; the rapid deformation stage induced by the combined action of mirabilite and ice crystal; the gradual deformation stage resulted from a small amount of ice crystals. During melting, the vertical deformation of soil mass underwent swift melting at a certain melting rate. For saline soil containing sodium sulfate, the curve of vertical deformation during freeze-thaw cycles against time presented a peach-shaped trend, and the vertical deformation rate of each cycle was basically consistent. The salt frost heaving rate increased with the proceeding of freezing and thawing. Higher salt content had more evident impact on vertical deformation. The research findings offer data support for revealing the hysteresis effect and also for the establishment of water-salt-thermo-mechanics coupling model.
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In order to provide technological reference for the design and construction of advanced level highway in the areas of crude coarse grain clay salty soil, based on the analysis of basic laboratory engineering character of crude coarse grain clay salty soil samples collected from Jiayuguan to Anxi section in G312, China, the representative crude coarse grain clay salty soil samples were selected for the freezing-thawing cycles test which lasted for 48 or 24 hours and were also selected for salt expansion tests with and without additional load. The salt expansion laws of crude coarse grain clay salty soil were researched by three kinds of testing methods. Results show that through freezing-thawing cycles test, crude coarse grain clay chloride sulfate salty soil has the phenomenon of volume contraction; the amount of salt expansion for crude coarse grain clay salty soil under additional covering load exceeds 80%. Comparing without additional load, the moving patterns of moisture contents and salt contents in soil column are different after several freezing-thawing cycles.
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The aim of this study is to explore the connection between salt expansion and frost heave in cooling sulfate saline soil. Freezing deformation tests are conducted on sulfate saline soil samples to examine the variations of salt expansion and frost heave of soil under varying water and salt content. The salt expansion and frost heave are controlled by changing the water content and salt content in the freezing process. Freezing temperature is set as the demarcation point identifying between salt expansion and frost heave. Results reveal a duplicate effect between salt expansion and frost heave in the freezing process, i.e. there is no positive correlation between total deformation of samples and crystalline volume. Total deformation obeys the law of the balance of power between salt expansion and frost heave, which means that total deformation reaches the minimum when salt expansion deformation equals frost heave deformation. The curve between total deformation and ratio of salt expansion displays an M-shape. The research findings are of active significance for further understanding the mechanism, building models, and hazard prevention of salt expansion and frost heave.
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Coarse-grained sulfate soil roadbeds are prone to excessive deformation problems, such as salt expansion and subsidence owing to changes in ambient temperature, and the impact on normal use of the roadbed cannot be ignored. In view of these problems, a test section was selected at the construction site of the Tehran-Qom-Isfahan high-speed railway project in Iran, and long-term monitoring of the roadbed temperature and moisture content was carried out. The variation of temperature and moisture content of the roadbed with time was analyzed. Based on this, a self-designed temperature change test device and field roadbed filling were used to conduct indoor temperature change cycle model tests to study the deformation characteristics of coarse-grained sulfate saline soil. The results show that during the monitoring period, the sensitive depth of the subgrade temperature in the field test is 0.22 m, and the moisture content of the subgrade within the depth of 1.0 m varies greatly. During the nine-cycle test, the temperature and moisture content of the sample depth in the range of 20 cm become more significant over time. However, with a change of the test temperature, there is a certain hysteresis in the change of sample temperature. The soil sample with 1.5% salt content shows salt expansion deformation and frost heave deformation in the first and second temperature change cycle tests, with a maximum deformation of 0.128 mm. The soil sample with 3% salt content exhibits such deformation in the first six cycles of the test, with a maximum deformation of 0.232 mm. Due to the influence of multiple factors such as temperature, ice-salt transformation, salt content, soil particle composition, and test cycle, specimens with different salt content eventually experience subsidence deformation after nine test cycles. The subsidence deformation of the sample with 1.5% salt content is 0.585 mm, which is 5.42 times the final subsidence deformation of the soil with 3% salt content. The research results can provide certain technical references for related projects.
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