The stability of loess high-fill slopes is a crucial issue in engineering, where the presence of fissures significantly impacts slope stability. This study investigates the seepage-mechanical response and fissure evolution characteristics of loess high-fill slopes under the coupled effects of consolidation, rainfall, and evaporation through model testing. The disaster chain evolution process of the slope under these coupled effects is revealed. The results show that the development of fissures in loess high-fill slopes does not follow a directional pattern and has a uniform influence on soil properties. Under rainfall, the slope exhibits preferential flow paths, which guide the deformation and failure modes. With the development of fissures, the fill material shows a cumulative damage effect, leading to progressive performance degradation and continuous decline in slope stability. This study enriches the theoretical framework for stability analysis of high-fill fissured slopes and provides guidance for disaster prevention and mitigation in loess regions.

With the advancement of ecological and environmental protection construction, the research on the modification of expansive soil using environmentally friendly polymers can make up for the harm to the ecological environment caused by traditional modification. Mechanical and microscopic properties of modified expansive soils were analyzed through indoor tests. The results showed that the liquid limit and plasticity index decreased by 52.14% and 77.36%, respectively, and the plastic limit increased by 20.83%. Maximum dry density decreased by 5.11% and optimum moisture content increased by 28.47%. The compressive and shear strength increases and then decreases with the increase of dosage, and the strength reaches the maximum when the dosage is 4%, and the vertical and lateral deformation of the specimen is the smallest. Modified soil swelling was reduced by 54.57% and swelling forces were reduced by 15-57%. The modified soil cracks developed slowly and the width of the cracks was reduced by 61.68% after the modification. Microscopy showed that no new minerals were generated after doping modifier, while hydrophilic minerals were reduced by 43.14%, and the gel film formed by hydration made the pores smaller and the structure tighter by filling and wrapping on the surface of the particles.

The Qinghai-Tibet Plateau (QTP) has an extensive frozen soil distribution and intense geological tectonic activity. Our surveys reveal that Qinghai-Tibet Plateau earthquakes can not only damage infrastructure but also significantly impact carbon dioxide emissions. Fissures created by earthquakes expose deep, frozen soils to the air and, in turn, accelerate soil carbon emissions. We measured average soil carbon emission rates of 968.53 g CO2 m(-2).a(-1) on the fissure sidewall and 514.79 g CO2 m(-2).a(-1) at the fissure bottom. We estimated that the total soil carbon emission flux from fissures caused by M >= 6.9 earthquakes on the Qinghai-Tibet Plateau from 326 B.C. to 2022 is 1.83 x 10(12) g CO2 a(-1); this value is equivalent to 0.51% similar to 1.48% and 2.34% similar to 5.14% of the increased annual average carbon sink resulting from the national ecological restoration projects targeting forest protection and grassland conservation in China, respectively. These earthquake fissures thus increased the soil carbon emission rate by 0.71 g CO2 m(-2).a(-1) and significantly increased the total carbon emissions. This finding shows that repairing earthquake fissures could play a very important role in coping with global climate change.

Expansive soils exhibit a relatively low permeability coefficient when structurally intact, allowing for their treatment as a homogeneous medium in calculations. However, the susceptibility of the slope's shallow area to numerous primary and secondary cracks under the influence of wetting and drying cycles challenges this approach. Failing to account for the impact of these surface cracks on the soil's permeability can result in a significant discrepancy between calculated and actual conditions. This study initially validated a predictive model for the soil-water characteristic curve that incorporates the effects of wetting and drying cycles. Subsequently, leveraging the fracture volume ratio parameter (pv) and the bimodal distribution characteristics of the dual-pore structure, we proposed a permeability coefficient model for expansive soils that considers fracture effects. This model was integrated with the validated soil-water characteristic curve model to facilitate the analysis of expansive soil's infiltration characteristics under cyclic wetting and drying conditions. The findings indicate that the predictive model accurately captures the hysteresis effect of expansive soil's soil-water characteristics. Moreover, the permeability coefficient model, which accounts for fractures, effectively reflects the infiltration properties of cracked expansive soil and enables the prediction and calculation of its permeability under multiple cycles of wetting and drying. This study introduces a predictive model for the soil-water characteristic curve, leveraging the hysteresis properties of expansive soil. Additionally, it presents a model for calculating the permeability coefficient of expansive soil, utilizing a dual-peak characteristic function. The development of these models establishes a theoretical basis for the computation and analysis of the soil's permeability attributes.

This study conducts several triaxial cyclic and plane strain cyclic impact tests on fissured soil under varying effective consolidation pressures, impact peak loads, and frequencies through the true triaxial test system to investigate the mechanical response characteristics. The results indicated that, under plane strain conditions, the specimens' shear resistance increases compared to that under triaxial loading. Moreover, the influence of fissures is challenging to quantify under triaxial loading compare to the mechanical response to fissure failure under the plane strain condition. As a result of the lateral confinement under plane strain conditions, the excess pore pressure, stress path, and lateral stress coefficient exhibit changes in sensitivity due to fissure damage, facilitating the analysis of the fissures' influence. Lower consolidation stress tends to increase the likelihood of fissure failure. As the peak impact stress escalates, the specimen deformation and excess pore pressure rise. When the impact peak stress reaches a critical value, the sample undergoes substantial deformation and fails rapidly. The impact of the frequency on specimen deformation correlates with the peak impact stress. Under low-impact peak stress, higher frequencies result in smaller deformations. However, under high-impact peak stress, a critical frequency exists. As the frequency increases, the difference between the maximum and minimum pore water pressure expands, with the change in this difference relating to fissure damage. Inherently, fissures in the soil significantly affect the mechanical properties under the impact load in the plane strain condition. The findings from this study can provide technical support for determining and evaluating the mechanical parameters of the fissured soil layer in light of the impact load.

Rapid dynamic loads, such as those caused by earthquakes or traffic, induce medium strain rates in expansive soil, impacting its mechanical properties, which are vital for geotechnical engineering design. This study aims to deepen understanding of the rate effect on expansive clay under plane strain conditions. It conducts various isotropic triaxial and plane strain shearing tests at different medium strain rates. Post-testing, the microstructures of the clay, affected by varying shearing rates, are examined using scanning electron microscope and nuclear magnetic resonance. The experimental findings revealed that the strength at higher strain rates surpasses that at lower ones. In addition, the strength under plane strain at the same consolidation stress level exceeds that under triaxial loading. The strain rate effect is more pronounced in the clay studied under low consolidation pressure, which is more significant in the triaxial state than under plane strain. Excess pore water pressure initially peaks at low strain rates before decreasing but increases at higher strain rates. The specimen's intermediate principal stress coefficient (b) rises with the increase in consolidation pressure and strain rate. In addition, the expansion of fissures and changes in internal structure account for the strain rate effect in undisturbed expansive soil under specific loading rates. These new insights aid in better understanding the behavior of expansive clay under medium strain rates, enabling engineers to establish appropriate design parameters and criteria. This ensures the safety and stability of structures under dynamic loading.

The Yuncheng Basin is part of the Fenwei Graben System, which has developed ground fissure hazards that have caused serious damage to farmland, houses, and roads and have brought about huge economic losses. Located in Wanrong County on the Emei Plateau in the northwestern part of the Yuncheng Basin in China, the Wangjiacun ground fissure is a typical and special ground fissure developed in loess areas, and its formation is closely related to tectonic joints and the collapsibility of loess. In order to reveal the formation and genesis of the Wangjiacun ground fissure, the geological background, developmental characteristics, and genesis pattern of the Wangjiacun ground fissures were studied in detail. A total of three ground fissures have developed in this area: a linear fissure (f1) is distributed in an NNE-SSW direction, with a total length of 334 m; a circular fissure (f2) is located near the pool, with a total length of 720 m; f2-1, a linear fissure near f2, has a fissure length of 110 m and an NE orientation. This study shows that tectonic joints in loess areas are the main controlling factors of the linear fissure (f1); differential subsidence in the pool caused by collapsible loess is the main source of motivation for the formation of the circular fissures (f2, f2-1), and tensile stresses produced by the edges of subsidence funnels lead to the cracking of shallow rock and soil bodies to form ground fissures (f2, f2-1). This study enriches the theory of ground fissure genesis and is of great significance for disaster prevention and the mitigation of ground fissures in loess areas.