Research on the deformation evaluation of loess under wet loading via structural yield behavior

Under wet loading, loess is prone to structural weakening and collapsible deformation. Existing indoor collapsible evaluation methods tend to overestimate the collapsibility of soil, causing engineering waste. Consequently, developing a simple and accurate collapsibility evaluation method is necessary. Taking Malan loess in Guyuan City as the research object, the study analyzed the influences of dry densities ( ρ d = 1.3, 1.4, 1.5 g/cm³) and water contents ( w = 6%~37%) on the compression and collapsibility deformation of loess through multi-stage water content confined compression tests.A total of 18 sets of samples and 216 sets of experimental data were completed. On this basis, the compression curves ( e -lg p ) under different experimental conditions were normalized.Finally, a simple and precise method for judging the wetting collapsibility of loess and predicting the wetting collapsibility coefficient is established. The findings of the study indicate that the structural yield stress ( p sc ) rises with an increase in ρ d and falls with anelevation in w . When the w is 6%, the p sc of the specimens with ρ d = 1.5 g/cm³ is increased by 16.81% compared to ρ d = 1.3 g/cm³, which is due to the increased number of particle contact points, contact area, and enhanced interparticle friction in a dense state, the structure is more stable.Collapsibility coefficient declines with the rise of w and ρ d , and it is not always positively correlated with pressure. After normalizing the e -lg p under various conditions, the data points decrease almost along the same curve. A power index normalization model is established and then is verified based on the internal modeling dataset. The measured data on both sides of the fitted curve are evenly distributed, with an R ² of 0.98, verifying the reliability of the model within the experimental conditions. This model is based on reshaping samples from a single soil source, and further validation is needed to promote it to other regions.A loess wetting collapsibility evaluation method based on the comprehensive physical index ( Z ) is proposed, which avoids the saturation deviation of traditional immersion tests and can simply and accurately evaluate the wetting collapsibility by establishing a quantitative relationship between Z , p sc , and the wetting collapsibility starting pressure. The study achievements can provide a basic reference for the preliminary identification of the collapsibility of loess.