The objective of this study was to enhance the mechanical properties of gravelly soil and to consider the binding and filling effects of xanthan gum and calcium lignosulfonate. To this end, gravelly soil samples were prepared with various dosages of xanthan gum and calcium lignosulfonate, and their curing effects were investigated. The mechanical properties and strength parameters of the cured gravelly soil were investigated using unconfined compressive strength (UCS) tests and conventional triaxial compression tests. Furthermore, scanning electron microscopy (SEM) was employed to examine the microstructure and curing mechanisms of the gravelly soil treated with these additives. The findings demonstrate that as the dosage increases, both xanthan gum and calcium lignosulfonate markedly enhance the compressive strength and shear strength of the gravelly soil. The curing effect of xanthan gum was found to be more pronounced with higher dosages, while the optimal curing effect for calcium lignosulfonate was achieved at a dosage of 4%. The gravelly soil treated with xanthan gum exhibited superior performance compared to that treated with calcium lignosulfonate when the same dosage was used. Moreover, at elevated confining pressures, the binding effect of xanthan gum and calcium lignosulfonate on the gravelly soil was less pronounced than the strength effect imparted by the confining pressure. This suggests that the impact of dosage on the shear strength of the gravelly soil is diminished at higher confining pressures. The stabilization of crushed stone soil by xanthan gum is a complex process that involves two main mechanisms: bonding and cementation, and filling and film-forming. The curing mechanism of calcium lignosulfonate-cured gravelly soil can be summarized as follows: ion exchange, adsorption and encapsulation, and pore filling and binding effects. The findings of this research offer significant insights that are pertinent to the construction of high earth–rock dams and related engineering applications.

Muddy siltstone combines the characteristics of both sandstone and mudstone, and is prone to instability over time. To study the long-term stability of tunnel engineering in this stratum, this article taking the cross-river metro tunnel section as the engineering background, and conducting research on the stress and deformation of the tunnel surrounding rock. Firstly, uniaxial compression creep tests were conducted on muddy siltstone to study the creep deformation law under graded loading. Secondly, a nonlinear damage creep model was established based on the Burgers model, and the experimental results were fitted. Finally, the proposed creep model was applied to the COMSOL Multiphysics numerical simulation software to perform multi field coupled calculations on the operation of metro tunnels. The research results show that: (1) Muddy siltstone undergoes the entire process of decaying creep, steady creep and accelerated creep. (2) The proposed nonlinear damage creep model can accurately describe the creep characteristics of muddy siltstone, especially in the accelerated creep stage. (3) Applying nonlinear damage creep model to tunnel numerical simulation calculation, it was found that the most obvious part of tunnel rock creep deformation is the tunnel arch crown. By comparing with on-site monitoring data, indicated that the established creep-fluid-structure coupling tunnel model can be used to predict surrounding rock deformation. The creep-fluid-structure coupling tunnel model proposed in this study provides a new perspective for the design and safety assessment of cross river tunnels in soft rock formations, which helps to achieve more accurate long-term stability prediction.

This study aims to analyze the impact of varying dosages of N-(n-butyl) thiophosphoric triamide (NBPT) on the physical and mechanical properties of microbial-induced calcite precipitation (MICP) grouting improved red clay. The research includes XRD and SEM experiments to examine the micro-structural characterization of the specimens and understand the mechanism of NBPT's action on MICP improved red clay. A comprehensive evaluation is conducted to assess the properties of red clay after the introduction of NBPT microbial improvement, the results show that The mechanical properties and peak strength of MICP improved red clay samples showed a tendency to increase and then decrease with the increase of NBPT doping, and the stress-strain curve showed a change from softening to hardening and then back to softening; the improvement effect was in the optimal state at the cut-off point when the doping amount of NBPT was 0.1%. The shrinkage deformation, initial water content, and shrinkage coefficient of the MICP improved red clay samples decreased gradually as the doping amount of NBPT increased. In the residual shrinkage deformation stage (δs2), the water content of the specimen needed to reach the ultimate linear shrinkage gradually increased with NBPT doping, causing it to enter the stable shrinkage deformation stage (δs3) earlier. The difference in CaCO₃ content between the upper and lower parts of the specimens gradually decreased with the increase of NBPT doping, and finally tends to be stabilized. The urease inhibitor NBPT can affect the crystal morphology and distribution of the product and intervene in the morphological transformation of vaterite to calcite.