Ili loess is susceptible to substantial collapsible deformation due to water infiltration, leading to various engineering failures. To investigate the characteristics of water infiltration and the mechanisms of collapsible deformation, a field immersion test was conducted in the collapsible loess region of Ili. The changes in water content, water diffusion form, infiltration water volume, and surface collapsible deformation during immersion were analyzed. Numerical simulations explored surface collapsible deformation characteristics under varying saturation infiltration ranges. The results showed that the average vertical diffusion rate in the experimental area was 0.38 m/d, while the average radial diffusion rate was 0.17 m/d. Over time, the water diffusion pattern transitioned from elliptical to conical, with a wet front angle of 41 and a saturated front angle of 20. The quantitative analysis of the vertical and radial water diffusion rates and infiltration water volume of Ili loess over time was conducted. A mathematical relationship between infiltration range and cumulative infiltration volume per unit area was derived. The correction coefficient for collapsible in the experimental area was determined to be 0.74, exceeding the recommended value of 0.5 in the specifications. The surface collapsible deformation correlates with water infiltration and can be divided into four stages: stable immersion, severe collapse, slow collapse, and consolidation settlement. As the saturation front angle increases, the surface collapsible deformation value maintains good consistency with the calculation results of the subsidence trough formula. The variation in the width of the subsidence trough aligns with the influence range of surface collapsibility, both following an exponential increase.

The research investigated the mechanical behaviors of ice- soil interface under different temperatures (- 1 degrees C, - 2 degrees C, and - 3 degrees C) and initial soil moisture contents (14%, 16% and 18%) using direct shear tests. The shear stresses of interface were described by generalized Duncan-Chang model and the shear stiffness expression of interface was derived. The results showed that at temperature of - 1 degrees C, the effect of initial moisture content on the interface strength was minimal. As the temperature drops to - 2 degrees C and - 3 degrees C, the higher initial moisture content in the soil enhances the bonding strength of interface. The shear stiffness and strength were sensitive to the initial moisture content at temperature of - 3 degrees C, as initial moisture content increases from 14 to 18%, the shear stiffness increases by 55.5% from 9.09 x 104 kPa/m to 2.04 x 105 kPa/m, the peak strength increases by 43.5% from 156.8kPa to 277.3kPa, and the residual strength increases by 51.1% from 114 to 233kPa. The finite element model of the ice- soil interface was established using COMSOL Multiphysics and the model parameters were assigned based on experimental results, the variations of Mises stress, displacement, friction stress, and adhesive stress of interface during shear process were analyzed.

The evolution of loess microstructure exerts a direct impact on its collapse evolution during dry and wet (DW) cycles. In this study, a hydro-mechanical coupling numerical model considering DW cycles and mechanical loading was established by extending the Barcelona Basic model, meanwhile combining with the test results to reveal the effect of DW cycling on the collapse deformation and strength response of loess. Additionally, the microscopic mechanism of loess collapse evolution was revealed through microscopic tests. Results indicated DW cycles caused the net compaction of loess, with the first DW cycle exerting the most significant effect on its deformation, consequently deteriorating the loess. Wetting under constant loading leads to a collapse of macrostructures formed by aggregates. Moreover, DW cycles transformed the structural units from line and surface contact to point. The basic structural units exhibited obvious grade properties, in which DW cycles trigger the collapse of compound aggregates, with the number of relatively stable mononuclear aggregates and intergranular pores increasing. DW cycles in an open environment induced the loss of cementing materials such as soluble salts and reduced the bonding strength among basic structural units. This subsequently tended to weaken the structural properties of loess and decreased the mechanical properties.

Investigations on the liquefaction resistance of an open-cast lignite mine soil under loading by earthquake-typical signals For the embankments of the planned opencast mining lakes in the Rhenish mining area, the proof of the stability under earthquake action must be provided. According to the guideline for the investigation of the stability of slopes in lignite opencast mines (RfS - Richtlinie f & uuml;r Standsicherheitsuntersuchungen [1]), the permanent slopes must be designed and constructed in such a way that a soil liquefaction is not to be expected. For the proof, in which actions and soil resistances are locally compared with each other, the irregular earthquake signal is converted into a regular signal with an equivalent number of cycles and constant amplitude. In this paper, this conversion is investigated for a typical earthquake signal of the Rhenish area, which was obtained from a dynamic finite element calculation. Triaxial tests with vertical cyclic loading and hollow cylinder triaxial tests with cyclic torsional loading are performed to investigate the liquefaction behaviour of an opencast mine soil under the influence of this earthquake signal. The results of these tests are compared with data from further tests with constant amplitude. It can be shown that the factor beta for converting irregular to regular signals depends on the type of loading and the magnitude of the static shear or deviatoric stress. On the basis of the experiments, recommendations for the choice of beta for the Rhenish mining area are given.