The weakening of loess structure under hydro-mechanical effect is an important reason for collapsible deformation of loess. Therefore, when establishing the constitutive model of unsaturated loess, it is necessary to consider the influence of loess structure to truly reflect the mechanical characteristics. A modified elastoplastic damage structural constitutive model (MEDSCM) is proposed for unsaturated Q(3) undisturbed loess based on the modified Barcelona basic model (MBBM), assuming that the yield stress of undisturbed loess is a coupling of remolded loess and structure, and adopting the non-associated flow rule. The structural evolution equations of unsaturated Q(3) loess in loading and collapsing are introduced respectively, and obtained the constitutive model of soil skeleton in loading and collapsing. There are a total of 18 parameters for the loading model and 15 parameters for the collapsibility model, which are determined by mechanical tests on unsaturated loess. By comparing the triaxial compression and collapsible test data with the model calculation results, the accuracy of the model is verified, and progress has been made in describing the weak hardening characteristics of unsaturated loess. The research results provide a new attempt for further understanding the mechanical properties of loess.

Vessel collisions pose significant threats on the safety of cross-channel bridges. Previous studies have paid little attention on the impact performance of common arch bridges with gravity foundations in inland waterways. This study aims to comprehensively investigate the anti-impact resistance and analyze the damage and failure mechanisms of arch bridges under vessel collisions. The entire process of vessel-bridge collision is simulated using three-dimensional explicit finite element technique. The damage characteristics, as well as the progressive collapse process of arch bridge are investigated thoroughly. Moreover, the rational calculation method for bridge lateral resistance against vessel collisions (BRaVC) is discussed. The results show that the gravity foundation bottom of arch bridge can be fixed in vessel-bridge collision numerical analysis due to insignificant foundation-soil interaction. The head-on barge collision on the bridge pier leads to indistinctive lateral displacement, while obvious local damage can be observed. The impact displacement of the bridge pier is not positively correlated with the impact energy according to the impact load spectra analysis. Barge collision on the main arch results in the progressive collapse of the bridge due to unbalanced horizontal thrust from the arch on the other side. The rational BRaVC can be calculated by using sectional strength based on elastoplastic analysis.

Artificial frozen sandy gravel exhibits the characteristics of wide distribution of particle size and complex composition, which are quite distinct from frozen fine-grained soils such as clay and silt. It may be more accurate to use both macroscopic and microscopic scales to evaluate the damage of artificial frozen sandy gravel. Therefore, this paper proposes an investigation on the macro-plastic damage and micro-crack damage of artificial frozen sandy gravel through triaxial compression and X-ray CT scanning tests. The two types of damage are obtained from completely different macro-plastic and micro-crack damage theoretical calculation methods. It can be concluded that the evolution law of the two damages is similar, but the value is different. Moreover, the defined cross-scale modified damage which is fitted through the calculated macro-plastic damage and micro-crack damage is proposed. The fitting functions reveal the evolution law of frozen sandy gravel damage more accurate, which is beneficial to the safety of the artificial ground freezing project and provides a valuable reference for subsequent numerical simulations of the frozen sandy gravel constitutive relationship.