Abstract
The salt expansion disease is severe for the soil containing sodium sulfate in cold regions. This paper carried out one‐dimensional salt expansion tests of saline soil, the crystallization test of saturated sodium sulfate solution, and the numerical cooling tests to explore the stability time of the salt expansion test and determine the standard procedure of salt expansion tests. The test results demonstrate that (i) the temperature equilibrium and the crystallization process are almost simultaneously completed in both sulfate saline soil and sulfate solution upon cooling; (ii) referring to the deformation equilibrium standard used in soil consolidation test, an expansion rate of less than 0.02 mm/h is suggested in the saline expansion test; and (iii) the equilibrium time is found to have a quadratic polynomial relationship to sample size and is much shorter under liquid bath conditions than under gas bath conditions. Based on these findings, a standard procedure of the one‐dimensional salt expansion test is proposed, in which the test equipment, the test process, the deformation stabilization time of salt expansion, and the data processing method are provided. As the deformation and the temperature are synchronized, the deformation stabilization time of samples with different sizes in different cooling media is recommended.
Highlights
Saline soil is widely distributed in northwestern China [1]
The sulfate crystallization effect and chemical reactions between sulfate and building materials will cause damage to building foundations, pile structures [2, 3], and slope structures [4]. e soil is defined as saline soil with soluble salt content equal to or greater than 0.3% [5]. e subgrade composed of sulfate saline soil is more vulnerable to diseases, such as dissolution, salt heave, frost heave, and mud boiling, among which the salt heave is the most severe disease [6]
Test Procedure under Air Bath Condition. e onedimensional salt expansion test procedure is as follows. e C4600 programmable constant temperature test chamber can automatically adjust the temperature change according to the set cooling program. e test uses 25°C ⟶ 12°C ⟶ 8°C ⟶ 4°C ⟶ 1°C as the cooling gradient. e cooling rate of the incubator cooling stage is set according to the test plan. e sample is cured at 25°C for 24 h, and the temperature is reduced to 12°C at the set cooling rate
Summary
Saline soil is widely distributed in northwestern China [1]. In the northwestern region, the sulfate crystallization effect and chemical reactions between sulfate and building materials will cause damage to building foundations, pile structures [2, 3], and slope structures [4]. e soil is defined as saline soil with soluble salt content equal to or greater than 0.3% [5]. e subgrade composed of sulfate saline soil is more vulnerable to diseases, such as dissolution, salt heave, frost heave, and mud boiling, among which the salt heave is the most severe disease [6]. E solubility of sodium sulfate decreases sharply with a decrease in the environmental temperature, accompanied by the salt crystallization and salt swelling effect in sulfate saline soil. Some researchers [9, 10] obtained the initial crystallization temperature of soils with different salt concentration contents through experiments. There still lacks a criterion for the stabilization time in the salt expansion test. (b) Determine the deformation stabilization time of the salt expansion test. Glauber’s salt in saline soil at different temperatures and established an empirical model for salt expansion. An essential influencing factor to the salt expansion test is the temperature stabilization time [29,30,31,32]. It is necessary to balance and determine a reasonable salt swelling
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