Fractal characteristics of sand grain group changes under freeze-thaw cycles and its correlation with long-term strength北大核心CSCD

Seasonally frozen soils are widely distributed in China in terms of area，and the freeze-thaw cycle effect generated by the alternation of cold and warmth is one of the causes of engineering damage in cold areas during construction，and it is particularly important to restore the nature and state of the soil when it is subjected to freeze-thaw action. Therefore，sandy soil specimens with different numbers of freeze-thaw cycles were prepared，and the long-term strength of frozen sandy soil was tested using a spherical template indenter. Using fractal theory and the microstructure image processing software ImageJ，the change law of grain group and long-term strength of two frozen sandy soils under different numbers of freeze-thaw cycles were studied. The results show that：for fine sand（FS），the fractal dimension DB has a highly significant positive correlation with the long-term strength variation，among which ≥0. 15~0. 20 mm and ≥0. 25~0. 40 mm have the best fit with the long-term strength，and are the dominant grain classes of FS. For medium sand（MS），the fractal dimension DB is slightly positively correlated with the long-term strength，and the variation shows a“vertical N”trend，in which the grain size content of ≥0. 30~0. 40 mm and ≥0. 40 mm fits better with the long-term strength，and is the dominant grain class for MS. The content of other grain groups did not correlate significantly with the long-term strength change. The freeze-thaw action changed the content ratios of coarse and fine grain agglomerates in the soil. With the increase of the overall particle size interval，the dominant particle size also increases，which shows that the long-term strength of frozen sandy soil tends to decrease and then increase with the increase of the content of some particle sizes. The results of the study can provide theoretical reference for the determination of long-term strength in areas subject to freeze-thaw action. © 2022 Science Press (China).

Fractal characteristics of sand grain group changes under freeze-thaw cycles and its correlation with long-term strength

Seasonally frozen soils are widely distributed in China in terms of area， and the freeze-thaw cycle effect generated by the alternation of cold and warmth is one of the causes of engineering damage in cold areas during construction， and it is particularly important to restore the nature and state of the soil when it is subjected to freeze-thaw action. Therefore， sandy soil specimens with different numbers of freeze-thaw cycles were prepared， and the long-term strength of frozen sandy soil was tested using a spherical template indenter. Using fractal theory and the microstructure image processing software ImageJ， the change law of grain group and long-term strength of two frozen sandy soils under different numbers of freeze-thaw cycles were studied. The results show that： for fine sand （FS）， the fractal dimension D_B has a highly significant positive correlation with the long-term strength variation， among which ≥0.15~0.20 mm and ≥0.25~0.40 mm have the best fit with the long-term strength， and are the dominant grain classes of FS. For medium sand （MS）， the fractal dimension D_B is slightly positively correlated with the long-term strength， and the variation shows a “vertical N” trend， in which the grain size content of ≥0.30~0.40 mm and ≥0.40 mm fits better with the long-term strength， and is the dominant grain class for MS. The content of other grain groups did not correlate significantly with the long-term strength change. The freeze-thaw action changed the content ratios of coarse and fine grain agglomerates in the soil. With the increase of the overall particle size interval， the dominant particle size also increases， which shows that the long-term strength of frozen sandy soil tends to decrease and then increase with the increase of the content of some particle sizes. The results of the study can provide theoretical reference for the determination of long-term strength in areas subject to freeze-thaw action.