To investigate the influence of sample preparation conditions and testing methods on the shear properties of compacted silt, samples with different moisture contents were prepared by saturation and drying methods. The shear mechanical properties of the samples were tested by direct shear and triaxial compression tests. When the designed moisture content wd of the sample is lower than the optimal moisture content wop, the structural strength of the drying sample is higher than that of the water-added sample, and the brittle failure is more obvious in the drying method, and the shear strength and parameters are larger. This is due to the influence of the gradation properties of the silt and the stress history in the process of sample preparation. When the intended water content of the sample is higher than the optimal water content, the mud particles are easily adjusted, and the deformation and stability process before shearing makes the two sample structures tend to be the same. So that the failure trend and shear strength properties are close to each other. Under the influence of the stress state of the sample in the direct shear and triaxial test and the uniformity of the distribution of clay particles in the water addition method, the change rule of the aggregate strength of silt particles on the shear surface is different with the thickness of the water film. The change rule of shear strength and water addition method parameters differs with the change of wd, while the shear strength and drying method parameters decrease with increasing wd.

In order to investigate the impact of plant root systems on the stability of loess shallow slope, this study conducted plant morphology investigations and direct soil shear tests to analyse the morphological characteristics of alfalfa and the shear characteristics of alfalfa root-loess composites under different soil bulk densities and soil moisture saturation levels. Additionally, the reinforcing effect of the alfalfa root system on the reliability of loess slopes was assessed using the Monte Carlo method. Slope reliability analysis refers to the estimation of the probability of slope failure under specific conditions. The results showed that plant weight and root weight both decreased following an exponential function with increasing soil bulk density. Root weight had a positively linear correlation with plant weight. The cohesion and internal friction angle of both loess samples without roots and with roots increased with increasing soil bulk density. The cohesion and internal friction angle of the two kinds of samples could decreased at less and more than 30% soil moisture saturation. The cohesion and internal friction angle of the root-soil composites were significantly higher than those of the rootless soil. The decrease of soil bulk density and the increase of soil moisture could increase the difference of the two mechanical parameters between the two kinds of samples. Assuming the thickness of the landslide body was 0.3 m, the failure probability of loess slopes covered with alfalfa significantly decreased from 34.97 to 14.51% compared to slopes without vegetation cover. Alfalfa roots significantly increased the reliability of the loess slopes in stability.

The mechanical properties of frozen-concrete interfaces affect the stability and durability of engineering structures in cold regions. To investigate these properties, laboratory tests and numerical simulations were conducted to study the mesoscopic evolution of the shear stress-displacement relationship and the shearing process at the interface. The direct shear tests were performed at different environmental temperatures (-2 degrees C, -5 degrees C, and -10 degrees C) and normal stresses (100 kPa, 200 kPa, and 300 kPa) on the frozen soil-concrete interface, and Particle Flow Code (PFC) model of direct shear was developed. The mesoscopic parameters (particle displacement, rotation, force chain, stress, coordination number, porosity, fabric, etc.) of the interface during shearing were simulated using the PFC model. Moreover, the relationship among the interface temperature, cohesion, and friction coefficient was determined based on experimental data, and the accuracy of the PFC model was verified using previous experimental data. The results of the PFC shear model aligned well with those of the laboratory test, and the formation of shear bands was simulated well. The displacement of the soil particles on the upper layer outside the shear zone was uniform, and the direction was the same, whereas the particles inside the shear zone showed significant differences in the dislocation and rotation of the soil particles. The force chain, stress field, coordination number, and porosity were similar in the shear process and showed a concentrated distribution in the opposite direction of the shear motion, which reflected the consistency of the microcosmic response of the particles under the action of macroscopic external forces. The regression equations for the temperature, cohesion, and friction coefficient in this study can be used to simulate the shear behavior of frozen soil-concrete interfaces under different temperatures and normal stresses.

Soil-rock mixture (SRM) is commonly used as backfill materials in high-fill roadbed slopes. The stability of these slopes depends on the mechanical properties of SRM, which are complex and difficult to accurately measure. To accurately assess the safety of the roadbed slopes constructed with SRM, it is crucial to develop a more precise experimental approach for investigating the shear mechanical properties of SRM. The discrete element method (DEM) is a powerful tool for analyzing the heterogeneous geomaterials. In this paper, a reverse reconstruction method to simulate rock blocks was initially proposed, along with a novel loading approach for simple shear tests. Subsequently, numerical models of SRM were established for direct shear and simple shear tests respectively. Finally, the shear mechanical properties of SRM under the two tests were systematically investigated, including block rotation, force chain distribution, crack distribution, particle damage state, normal displacementshear strain curve, and shear stress-strain curve. The numerical results demonstrate that, compared to the direct shear test, the shear zone of SRM in the simple shear test exhibits a more uniform distribution, with a greater thickness of the shear zone and a larger rotation angle of principal stresses. Therefore, the simple shear test is more representative of the actual slope load conditions and provides more accurate shear strength parameters.

To improve the substandard engineering properties of saline soil in cold regions and to mitigate the environmental pollution caused by conventional calcium-based stabilization materials, ionic soil stabilizer (ISS) along with lime and fly ash are added to saline soil. Triaxial tests and discrete element numerical simulations are employed to investigate the macro-microscopic mechanical properties of the ISS stabilized saline soil in a frozen state. The results demonstrate that adding ISS significantly improves the mechanical properties of lime and fly ash-stabilized saline soil under frozen conditions. The strength of the ISS stabilized soil reaches its peak at an ISS content of 3 %, but further increase in ISS content leads to a decrease in strength. The discrete element method (DEM) indicates that a failure surface forms an angle of approximately 55 degrees degrees to the horizontal plane, with particle displacement symmetrical about the failure surface. The pore structure is significantly influenced by confining pressure during loading, and a quantitative analysis is conducted on the changes in porosity and coordination number. This research offers valuable insights for improving the undesirable engineering properties of saline soil in seasonal frozen regions using ISS and for studying its macro-microscopic mechanical characteristics. Additionally, it contributes to reducing the use of inorganic materials, thereby promoting environmental protection.

The macroscopic and microscopic mechanical characteristics of subgrade soil in cold regions play an important role in the stability of embankment engineering in cold regions. In this study, we conduct triaxial tests and isotropic loading -unloading tests on frozen clay in the cold region subgrade. The tests are conducted under different temperatures and confining pressures to obtain its macroscopic strength and deformation characteristics. Meanwhile, we establish a discrete element model of frozen clay based on the Discrete Element Method (DEM) to simulate conventional triaxial and isotropic loading -unloading tests, and analyze its mechanical characteristics from a microscopic perspective. The results of the study indicate that the strength and deformation of frozen clay are greatly affected by the cooling temperature and confining pressure. As the cooling temperature decreases, the cohesion of the specimen significantly increases, and the internal friction angle slightly increases, along with the elastic moduli. Under low confining pressure, the specimen exhibits significant volumetric expansion, while under high confining pressure, the specimen mainly undergoes volumetric contraction. Through discrete element numerical simulation, we obtain the microscopic mechanical characteristics of frozen clay, explain the bulging phenomenon of the specimen from a microscopic perspective, and verify the applicability of the flexible membrane. Meanwhile, the influence rules of various microscopic parameters on the mechanical properties of frozen clay are also obtained through a series of parameter calibration works.

A series of large-scale direct shear tests were carried out to study the stress -strain relationship of the interface between the spoil mixture and concrete under different roughness conditions. The results showed that roughness significantly affects the shear strength properties and dilatancy characteristics of the interface. Under different roughness conditions, the shear stress ratio and the normal deformation of the interface tend to be stable after larger shear strain, and the interface presents the characteristics of a critical state. With the increase of shear strain, the void ratio of the interface shows the law of transformation from the initial void ratio to a certain stable void ratio. Based on the void ratio prediction formula of the interface, the relationship between roughness and critical state parameters was established, and the interface state parameters were introduced into the hyperbolic model. Finally, a state -dependent hyperbolic model of the interface considering the roughness was established. Importantly, the model can well reflect the shear stress -strain relationship of the interface under different roughness conditions.

For the high-fill slope with soil-rock mixtures (SRMs), the bedrock under the SRMs can be excavated into many benches to improve the mechanical properties of bedrock-SRMs interphase and the stability of the slope. However, this improvement effect by bench size is still unclear. The continuous-discrete coupled method is a powerful tool for analyzing the interaction between soil and structure, soil and rock, etc. Firstly, this paper proposes a fine discrete element modeling method for rock blocks and develops a continuous-discrete coupled method for the benched bedrock-SRMs interphase. Then, a series of numerical direct shear tests for the benched bedrock-SRMs interphases with different bench sizes are conducted. The effect of bench size on the shear mechanical properties of the interphase is systematically investigated in terms of rock block rotation, contact force chain distribution, crack distribution, shear stress-displacement curve, and shear strength. The numerical results demonstrate that the bench size has a considerable impact on the strength and deformation properties of interphase. Raising the height or height-width ratio of the benched bedrock can enhance the interaction and skeletons between the benched bedrock and SRMs, thereby improving the strength and deformation properties of the interphase. Compared to increasing the bench height, increasing the height-width ratio has a more significant effect. Finally, a shear strength prediction method for the benched bedrock-SRMs interphase is proposed based on the Mohr-Coulomb strength criterion, which is practical in the design and stability evaluation of high-fill slope with SRMs. A reverse reconstruction method for building the refined SRMs model is proposed.A coupled FDM-DEM is proposed to simulate the benched bedrock-SRMs interphase.The impacts of bench size on mechanical properties of the interphase are discussed.A shear strength prediction method for the interphase is proposed.