In the loess-filling project, the original structural loess under the filling will produce creep deformation under the isometric consolidation stress state, affecting the upper building's safe construction and later operation. Therefore, studying the creep deformation characteristics of structural loess under different consolidation coefficients is significant. In this paper, the following results are obtained by combining test and theoretical analysis. In view of the structural loess under the filling, the triaxial creep test of undisturbed loess under different isometric consolidation coefficients, confining pressures and shear stress levels was completed, and the creep deformation law of structural loess was obtained. The creep characteristics of undisturbed loess are found to be diversified under different coefficients, confining pressures, and shear stresses, including initial instantaneous deformation, subsequent creep attenuation deformation, and final stable creep deformation. The damage creep constitutive model of undisturbed loess is established, taking the binary medium model as the framework, the cementation element adopts the Nishihara model, the friction element introduces the overstress model and considers the isometric consolidation effect, and the damage creep constitutive model of undisturbed loess is established. The theoretical model is obtained by determining the relevant parameters of the constitutive model. The theoretical curve is compared with the experimental curve and shows that the damage creep model established in this paper can better reflect the creep of structural loess under isometric consolidation conditions well. The research results can provide systematic theoretical support and an experimental basis for the deformation problems involved in the filling project in the loess area.

Disintegration fragments the loess body, causing erosion and the emergence of significant geohazards. The impact of vibrations on soil disintegration has been slightly documented; however, the contribution and mechanism of train vibration frequency in the disintegration of undisturbed loess remain unclear. In this study, train vibrations were monitored in situ, and the resulting vibrational parameters were used in loess disintegration tests using a customised vibration-disintegration apparatus. The changes in the meso-parameters of the disintegrated loess and aqueous solutions were quantified, and the microstructural differences in the residual loess after disintegration were compared under non-vibrating and vibrating conditions. The results revealed that train vibrations in the loess progressively diminished with increasing distance from the track, with dominant vibration frequencies ranging from 17 to 49 Hz. Increasing the vibration frequency accelerated loess disintegration and enhanced the dispersion of the disintegrated fragments. Notably, the acceleration effect of disintegration was particularly pronounced in the early stages of increasing vibration frequency, and it tended to plateau above 15 Hz. The relationship between the vibration frequency and disintegration velocity (DV) of loess influenced by the initial water content can be expressed as a power function with variables. Vibrations accelerate loess disintegration primarily attributed to repetitive particle displacement and the vibrations of free water in the pores which lead to frictional damage to the weakly cemented structure and pore expansion. Higher vibration frequencies generate greater inertial forces and facilitate more frequent particle jumps, allowing the loess to reach the disintegration threshold conditions more readily than at lower frequencies. These findings provide theoretical value for the prevention and mitigation of water-induced loess geohazards and land degradation in vibrating environments.

On July 20, 2021, over 2000 ground subsidence events and collapses occurred in Zhengzhou, China, after a heavy rainstorm. These events were mostly caused by the reduced mechanical properties of loess under moistening and repeated dynamic loading. After the conducted dynamic triaxial tests considering varying moisture content, envelope pressure and 10,000 vibrations, the dynamic properties evolution of undisturbed loess under moistening has been clarified. The experimental results showed that the dynamic strain of undisturbed loess under moistening conditions increases gradually with increasing dynamic stress, following the Hardin-Drnevich hyperbolic model. The initial dynamic shear modulus, maximum dynamic shear stress, and dynamic strength decrease linearly with increasing moisture, while the dynamic strain is the opposite, and the damping ratio is less affected by the increased moisture. The dynamic strain rises with increasing dynamic stress and moisture content considering the same vibrations. Increased vibrations and greater moisture content under identical dynamic stress cause a faster accumulation of dynamic strain in undisturbed loess, making it more susceptible to damage. The results are of guiding significance for the evaluation and analysis of the dynamic properties of loess and provide technical support for disaster prevention and mitigation in Zhengzhou.

To solve the problem that the mechanical behavior of undisturbed loess in seasonally frozen soil area is affected by freeze-thaw action, triaxial shear tests of undisturbed loess under freeze-thaw condition were carried out. The results show that the mechanical properties of undisturbed loess are greatly affected by factors including freeze-thaw process, water content, natural density and confining pressure. Freeze-thaw action has a certain impact on the failure surface shape and stress-strain curve. Before and after freeze-thaw, the shape of the shear failure surface is complex, including single oblique failure surface, double oblique failure surface, vertical failure surface, X-shaped failure surface, bulging failure, etc. And under the conditions of low water content, low confining pressure and high dry density, the stress-strain curve tends to be softened. Conversely, the curve tends to harden. Freeze-thaw action can make the stress-strain curve transition from softening to hardening. In addition, the freeze-thaw action significantly weakens the failure strength, shear strength, cohesion, initial tangent modulus and failure ratio of undisturbed soil, but does not change the internal friction angle obviously. Also, the heterogeneity of natural soil is also an important factor affecting the mechanical parameters, failure surface shape and stress-strain curve of undisturbed loess.

During tunnel excavation in loess, the surrounding loess at vault and waist exhibits deformation and structural strength anisotropy. Structural strength plays an important role in the mechanical and deformation characteristics of loess, which are clearly discussed in this paper. Undisturbed loess samples were taken from the Wangjiagou and Gongjiawan Tunnels in northwestern China. A series of tests including triaxial shear, unconfined compression, tensile strength, loading-unloading cycles, and confined compression were conducted on undisturbed loess in the vertical and horizontal sampling directions. Considering the influence of loess structure on its anisotropy, a scanning electron microscopy (SEM) test was also performed to analyze the main reasons for the anisotropy of undisturbed loess. The results indicated that the ratio of strain in the horizontal direction to that in the vertical direction decreased with increasing confinement pressure, but first increased and then decreased with increasing normalized deviated stress. The deformation parameters of undisturbed loess were anisotropic. The ratio of vertical to horizontal elastic modulus, the lateral compression modulus, the pre-consolidation pressure, and the compression coefficient of undisturbed loess were respectively 1.20, 1.15, 1.35, and 0.88. A geometric model of the structural strength anisotropy of undisturbed loess was also constructed, and related structural strength parameters were also proposed.