The consequences of changes in the structure of loess as a result of cyclic freezing and thawing

Abstract

The effects of freeze/thaw cycles change the structure of loess, which causes the deterioration of the specimen strength, leading to the occurrence of engineering disasters. In order to study the structure changes of loess body under freezing/thawing environment, taking Yanan city in Huangling County loess as the test object, this paper investigates the changes of the structure under different initial water content and different freezing/thawing cycles, and then analyzes the test results based on computer image processing technology, defines the damage variables, and quantitatively evaluates the damage state of the specimen. The results show that, with the increase of freezing and thawing times: the frost heaving force appears continuously; in the pores, the ice-water phase change volume expands; the local micropore stress concentration causes the specimen skeleton connection mode to change, from the surface–plane contact to the point–surface, point–point contact; the specimen structure is damaged by the number of fissures; and the total area changes. Therefore, this paper defines the porosity as a damage variable. As long as the damage variable and its evolution rule are known, the damage behavior of the material can be described, the damage variable increases with the increase of the freezing/thawing cycle, the specimen structure deteriorates, and the high density area of the specimen decreases, the low density area increases, and the integrity of the loess decreases. The continuous development of specimen porosity and fissure makes the migration channel change continuously, causing transfer channel elongation, widening, and new channel generation, resulting in the increase of ice generation.