Abstract
To investigate the mechanical properties of frozen saline soil, the deep calcareous clay in the Huanghuai mining area was chosen as the research object, and an orthogonal test was carried out to study the true triaxial mechanical properties of frozen saline calcareous clay under the influence of multiple factors. The stress–strain characteristics, strength, and influence trend of salted frozen calcareous clay with different salt content, stress paths, and water content, and the relationships among the above-mentioned factors, were investigated. The analysis of the test results by an orthogonal test revealed the order of importance of the factors that influenced strength. The primary and secondary order of influence σ1 is as follows: confining pressure σ3, water content ω, temperature T, medium principal stress coefficient b, and salt content φ. Under the influence of multiple factors, the strength of frozen soil in the real state is not the result of single factors with independent influences that are then simply superimposed. Instead, the complex interactions of various factors affect strength. The stress path significantly influences the stress–strain relationship of frozen calcareous clay. As the coefficient of the intermediate principal stress b increases, its influence on the strength of salted frozen calcareous clay diminishes, and the optimal principal stress coefficient b = 0.33 maximizes the strength of the specimen. The influence of the moisture content on the strength of the sample is negatively correlated. The effect of different moisture contents on the deformation and failure characteristics of unsaturated saline calcareous clay is not significantly different, and this difference does not exceed 5%.
Highlights
More water in the soil means that the volume of ice crystals increases at low temperatures, which in turn increases the strength of frozen soil [14]
When the middle principal stress coefficient b increased from 0.67 to 1, the large principal stress increased from 11.067 MPa to 11.193 MPa, which marks an increase of only 1.13%, and the intermediate principal stress increased from 8.622 MPa to 9.079 MPa, which marks an increase of only 5.03%
When the water content ω increased from 17.5% to 20%, the large principal stress decreased from 9.258 MPa to 7.855 MPa, which marks a decrease of 15.15%, and the intermediate principal stress decreased from 8.111 MPa to 7.357 MPa, which marks a decrease of 9.30%
Summary
The artificial ground freezing curtain is used as a temporary support measure for underground structures because it creates dry conditions for underground engineering construction. Previous studies [26,27] have investigated the influence of water content, consolidated confining pressure, the coefficient of intermediate principal stress, and intermediate principal stress ratio on the strength of frozen clay through true triaxial tests. The above-mentioned studies clarified the unilateral relationship between the compressive strength of frozen soil and the temperature, water content, salinity, and coefficient of intermediate principal stress, but did not investigate the strength characteristics of frozen soil under the influence of multiple factors. This study selected the deep calcareous clay in the Huanghuai mining area as the raw material and investigated the relationship between the strength of the frozen calcareous clay and different water content, salt content, temperature, confining pressure, and principal stress coefficient b by artificially mixing water and CaCl2.
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