The physical and mechanical characteristics of saline soil are significantly influenced by salt content, with macro- and mesoscopic mechanical properties closely correlated. This study investigates the strength and deformation behaviors of saturated saline sand through indoor triaxial shear testing under varying confining pressures and salt contents. The key innovation lies in developing a coupled finite element and discrete element analysis model to simulate the mesoscopic behavior of saline sand under triaxial shear stress state. Flexible boundary conditions were applied, and appropriate contact models for salt-sand interactions were selected. By adjusting mesoscopic parameters, stress-strain curves and variations in porosity, coordination number, particle displacement, and contact force chains were analyzed. The study further explores shear band development and shear failure mechanisms by examining relative particle displacement and the breaking of contact force chains. Additionally, the influence of salt particle size on the overall strength of the DEM model was assessed. The findings provide valuable insights into the internal structural changes of saline sand during shear deformation, contributing to a better understanding of its mechanical behavior in engineering applications.

A large diameter triaxial specimen of 61.9 mm was made by mixing coconut shell fibers with red clay soil. The shear strength of coconut shell fiber-reinforced soil was investigated using a dynamic triaxial shear test with confining pressure in a range of 50-250 kPa, a fiber content of 0.1%-0.5%, and a loading frequency of 0.5-2.5 Hz. The Hardin-Drnevich model based on the coconut shell fiber-reinforced soil was developed by analyzing and processing the experimental data using a linear fitting method, determining the model parameters a and b, and combining the influencing factors of the coconut shell fiber-reinforced soil to improve the Hardin-Drnevich model. The results show a clear distinction between the effects of loading frequency and fiber content on the strength of the specimens, which are around 1 Hz and 0.3%, respectively. Hardin-Drnevich model based on coconut shell fiber-reinforced soil can better predict the dynamic stress-strain relationship of coconut shell fiber-reinforced soil and reflect the dynamic stress-strain curve characteristics of the dynamic stress-strain curve coconut shell fiber-reinforced soil.

Resourceful utilisation of tailings waste remains a hotspot in global research. While silica-aluminate-rich copper tailings can serve as raw materials for geopolymer preparation, their high Si/Al ratio significantly limits the geopolymerization degree. This study investigates the feasibility of developing copper tailings-based geopolymers for road base applications, using copper tailings as the primary raw material supplemented with 30 % soft soil, 15 % fly ash, and 5 % cement. The effect of NaOH content on the strength characteristics of copper tailings-based geopolymers was explored by the unconfined compressive strength test and triaxial test. The mineral composition and microstructure of copper tailings-based geopolymers specimens were characterised based on the microscopic technique. The results show that: (1) With the increase of NaOH content, the unconfined compressive strength of the copper tailings base polymer increases and then decreases, and reach the maximum value when the NaOH content is 1 %. Compared with the sample without NaOH, the addition of 1 % NaOH increased the unconfined compressive strength by 47 % at the early stage and 69 % at 28d curing age. (2) An optimal NaOH content significantly improves the shear performance of the copper tailings-based polymer, primarily by enhancing its cohesion. Triaxial test results demonstrate that 1 % NaOH addition increases cohesion by 73 % at 28d curing age. (3) The NaOH promotes the formation of geopolymer gel, refines the pore structure, and increases sample density, thereby enhancing strength. Overall, the research results can provide a reference for the application of copper tailings solid waste in roadbed materials.

The structure, strength, and deformation characteristics of artificial structural loess can be manually controlled, which has significant advantages in scientific research on loess. By preparing and testing artificial structured loess, the natural properties of structured loess can be better investigated and studied. In this paper, the influence of varying moisture contents and additive dosages on artificial structured loess strength characteristics through triaxial shear tests were analyzed. The moisture content and additive dosage reflecting the structural properties of natural loess were obtained. Based on the microscopic test results, the mineral components, micromorphology, and pore characteristics of artificial structural loess were analyzed, and the mechanism of the structural evolution of loess under mechanical action was revealed. The results show that the minimum differences in the peak strength between W-16-Y2.0C2.0 and undisturbed soil under confining pressures of 50, 100, and 200 kPa are 6.481 kPa, 7.676 kPa, and 4.912 kPa, respectively. The minimum differences in the cohesion and inner friction angle between W-16-Y2.0C2.0 and undisturbed soil are 2 kPa and 0.2 degrees, respectively, indicating that W-16-Y2.0C2.0 is the optimal structural soil with a structural strength closest to that of undisturbed soil. Compared with the undisturbed loess, the content of calcite in the artificial structure loess increases from 9.8% to 11.2%, the proportion of plagioclase decreases from 20.5% to 17.4%, amphibole is consumed completely, and 2.1% of halite is generated. Furthermore, the pores of structured soil exhibit a three-peak distribution and are divided into four types, including micropores (= 13.5 mu m). When the pressure increases from 50 kPa to 200 kPa, micropores increase by 4.67%, small pores increase by 4.97%, medium pores decrease by 2.4%, and large pores decrease by 7.24%. The trend of pore structure changes in W-16-Y2.0C2.0 is similar to that of undisturbed loess. The research results provide a reference for preparing and applying artificial structural loess.

After the construction of the frozen wall of the vertical shaft is completed, it will undergo a long thawing process. Accumulation of damage under load may lead to the rupture of frozen walls and cause engineering accidents. The changes in mechanical properties during the thawing process of frozen rocks are key issues in controlling the stability of frozen walls. In view of the instability problem of the frozen wall of the vertical shaft, this article chooses the saturated sandstone of the Cretaceous system as the research object. Conduct triaxial compression tests under different temperature and confining pressure conditions. Obtain relevant parameters for analysis. And nuclear magnetic resonance technology was used to detect the changes in pore water content in saturated sandstone at different temperatures. The results indicate that: (1) At room temperature, pore water mainly exists in the form of free water, while at low temperatures, pore water mainly exists in the form of adsorbed water. (2) Compared with frozen soil, frozen rocks also exhibit significant supercooling phenomena. (3) According to the variation of unfrozen water content in saturated sandstone at different temperatures, it can be divided into three stages: freezing cessation (- 20 degrees C similar to - 6 degrees C), stable freezing (- 6 degrees C similar to - 2 degrees C), and rapid freezing (-2 degrees C similar to 20 degrees C). (4) As the temperature increases, the closure level of saturated sandstone gradually increases, while the initiation and expansion levels gradually decrease. (5) There is an exponential relationship between the unfrozen water content and the peak strength of saturated sandstone, with a good correlation. And show the same trend of change under different confining pressures. The research results can provide theoretical support and experimental basis for evaluating the instability and failure induced by thawing of frozen walls.

This study systematically examines the influence of joints on the mechanical properties of loess, highlighting the impact of joint dip angles on soil deformation and failure mechanisms. By employing an innovative layered compaction method to prepare jointed specimens, and conducting comparative experiments with different simulation materials (wax paper, rice paper, and plastic film), a series of controlled indoor triaxial compression tests were performed. The key findings are as follows: (1) The joint dip angle plays a decisive role in the evolution of failure mode, with five typical failure mechanisms identified based on fracture characteristics: shear failure, sliding failure, conjugate shear failure, sliding-shear failure, and sliding-conjugate shear failure. (2) The weakening effect of joints exhibits confining pressure dependency: Under low confining pressure (50 kPa), jointed specimens demonstrate increased axial displacement and a reduced shear strength attenuation ratio. (3) Mechanical parameters are significantly influenced by the dip angle: When the joint dip angle falls within the critical dip range of 60 degrees-75 degrees, both cohesion and internal friction angle reach their minimum values, forming zones of weakened mechanical properties. (4) A comparative analysis of simulation materials indicates that single-layer rice paper, due to its optimal thickness and tensile strength, effectively replicates the contact behavior of natural joint surfaces. This study establishes the quantitative relationship between joint geometric parameters and mechanical responses, providing an experimental basis for the engineering geological assessment of loess.

In order to study the strength characteristics of organic-matter-contaminated red soil and the improvement effects of different modifiers, the red soil in the Yulin area was taken as the research object, and triaxial compression tests were carried out to study the effects of different mass fractions (0%, 2%, 4%, 6%, 8%) of organic matter (sodium humate) on the strength characteristics of red soil. Unconfined compressive strength (UCS) tests and scanning electron microscopy (SEM) tests were carried out to study the improvement effects of different amounts of lignin, fly ash, and xanthan gum on organic-matter-contaminated red soil (organic matter content of 8%). The results of the tests showed that the cohesion and internal friction angle of red soil both tended to decrease with the increase in organic matter content. When the organic matter content increased from 0% to 8%, the cohesion of the red soil decreased from 60.98 kPa to 40.07 kPa, a decrease of 34.29%; and the internal friction angle decreased from 17.42 degrees to 7.28 degrees, a decrease of 58.21%. The stress-strain relationship curves of organic-matter-contaminated red soil all show a hardening type. Under different confining pressures, as the organic matter content increased, the shear strength of the red soil decreased continuously. The unconfined compressive strength of organic-matter-contaminated red soil increased with the increase in lignin content, and increased first and then decreased with the increase in fly ash content and xanthan gum content. Through comparative analysis, it was found that the fly ash with a content of 15% had the best improvement effect. The lignin-amended red soil enhanced the connection of soil particles through reinforcement, reduced pores, and improved soil strength. Fly ash improved the acidification reaction, and the hydrates filled the pores and enhanced the soil strength. Xanthan gum improved the red soil by absorbing water and promoting microbial growth, further enhancing the bonding force between soil particles. This study can provide a reference for engineering construction and red soil improvement in red soil areas.

Chemical stabilization is among the methods utilized to improve the shear strength properties and volumetric changes of problematic soils. This research assesses the possibility of using sludge ash from a wood and paper mill (SAWP) as an industrial sludge to improve the fat clay engineering characteristics. Thus, unconsolidated-undrained triaxial, direct shear, one-dimensional swelling, and consolidation tests were conducted. Results showed that shear strength parameters (both in short and long-term) increase with increasing SAWP contents and curing period due to the production of sufficient cementitious components and the formation of strong bonds between the particles. Investigating the direct shear test results indicated that the failure envelope in stabilized samples with high SAWP contents was slightly curved. Stabilized samples with high amounts of SAWP at low vertical stresses show brittle failure, while the type of failure observed for these samples at high vertical stresses is more ductile. Moreover, the magnitude of free swell gradually decreased with increasing SAWP contents. The replacement of clay particles with SAWP and flocculation and/or agglomeration of clay particles were the main reasons for this issue. Finally, the compression index, swell index, and coefficient of volume compressibility decrease with increasing SAWP content for the applied load increment, indicating the effect of stabilization in reducing the consolidation settlement of the layers. The test results revealed that the sludge ash used in this study can be used to enhance the engineering properties of fat clay.

To investigate the efficacy and strength properties of Fe2+-activated persulfate remediation for 1,2-dichlorobenzene-contaminated soil with varying persulfate concentrations, we conducted degradation, microscopic, particle size, liquid-plastic limit, unconfined compressive strength (UCS), and undrained shear tests. The results indicate that adding 15.0% Fe2+-activated persulfate achieves a 92.59% removal rate of 1,2-dichlorobenzene. Furthermore, the reaction produces sodium sulfate, calcium sulfate, and ferric hydroxide. Small amounts of sodium sulfate and calcium sulfate fill the pores between soil particles, leading to a denser soil structure. However, the expansive effect of excessive sodium sulfate crystals weakens the inter-particle cohesion, leading to soil loosening. After remediation, the clay content increases, while the silt and sand content decreases. The liquid limit, the plastic capacity and the plastic index increase, while the plastic limit decreases with the increase of the persulfate dosage. The UCS and the maximum shear stress decrease with the increase of the persulfate dosage. The UCS of the soil treated by 10.0% persulfate is 310.75 kPa, 20.34% higher than the strength of untreated soil. The maximum deviator stress at shear failure is 142.73 kPa.

Against the backdrop of saline soil solidification and the resource utilization of solid waste and aeolian sand in cold and arid regions, this study employs locally accessible fly ash and aeolian sand to solidify saline soil. By combining unconfined compressive strength tests, X-ray diffraction analysis, scanning electron microscopy, orthogonal experiments, and single-factor analysis, the strength characteristics, mineral composition, and interfacial structure changes of saline soil solidified with different freeze-thaw cycles and varying amounts of fly ash, aeolian sand, and alkali activators were investigated. The effects of each factor were analyzed to determine the optimal mixture ratio and to explore the solidification mechanism.The results indicate that the unconfined compressive strength of saline soil is most significantly enhanced when solidified with a combination of fly ash, aeolian sand, and alkali activators. The optimal mixture ratio was found to be 24 % fly ash, 7 % aeolian sand, and 4.5 mol/L alkali activator. With the incorporation of these solidifying materials, the failure mode of saline soil transitions from plastic to brittle, and the stress-strain curve exhibited a strain-softening behavior. The combined solidification method demonstrated the most pronounced effect in mitigating freeze-thaw damage, with the unconfined compressive strength of the solidified soil reaching 7.01 MPa after seven freeze-thaw cycles, compared to 0.03 MPa for the untreated soil, an increase by a factor of 234.This significant enhancement is attributed to the formation of substantial gel substances, which mitigate the strength loss caused by freeze-thaw cycles. The gel locking mechanism between particles in the solidified soil far exceeds the detrimental effects of freeze-thaw cycles, effectively inhibiting freeze-thaw deterioration. Additionally, the reaction pathways involving AFt and AFm phases reduce the content of SO 4 2- and Cl-in- in the solidified soil, effectively suppressing salt expansion and significantly improving the soil's strength.