The Metro Jet System (MJS), widely utilized for reinforcing weak foundations, relies critically on the mechanical properties of its piles to ensure effective soil stabilization. Unlike laboratory-scale tests that often overlook real-world constraints and soil heterogeneity, this study conducted full-scale field experiments to replicate in-situ MJS pile formation. Core samples extracted post-construction were analyzed to evaluate the effects of cement content, radial non-uniformity, and surrounding soil characteristics on compressive strength, stress-strain behavior, and failure modes. Complementing the experiments, discrete element numerical simulations were employed to microscopically validate the mechanisms underlying macroscopic observations. The research findings indicate that the stress-strain relationship of the pile specimens exhibits strain-softening behavior, and post-peak brittleness of the specimens increases with higher cement content. The mechanical properties of the pile body specimens are significantly influenced by cement content and distance from the pile center, with less correlation to the strength of the surrounding strata. Higher cement content, shorter distance from the pile center, and increased strength are observed to be interrelated. Numerical simulation results show that as cement content increases, the rate of reduction in the coordination number of the specimens decreases. In the early stages of numerical experiments, the rate of increase in the number of cracks becomes progressively lower. A numerical model considering cement content for the mechanical properties of the piles was established, demonstrating good predictability for pile compressive strength. These results underscore the necessity of full-scale testing for reliable in-situ performance assessment and provide actionable insights for optimizing MJS pile design in geotechnical engineering.

Loess is a distinctly structured soil. Undisturbed loess is prone to geological hazards, such as liquefaction and landslides under dynamic loads. There are also problems such as the inhomogeneity, anisotropy, and disturbance of in situ sampling. An artificial structural loess is prepared to accurately display the dynamic characteristics of undisturbed loess. This study took artificial structural loess as the study object, through dynamic triaxial tests, analyzed the effects of the confining pressure (sigma 3), dry density (rho d), and cement content (D) on its dynamic strength. Then, a dynamic strength index model of artificial structural loess was established. Our results show that the dynamic strength of artificial structural loess rises with enhanced sigma 3, rho d, and D. The dynamic cohesion (cd) and dynamic friction angle (phi d) increased with the rise of rho d, and D. The dynamic strength of artificial structured loess is closer to that of undisturbed loess when the rho d is 1.60 g/cm3 and D is 2%. The R2 values of the phi d and the cd model were 0.97 and 0.98, respectively, fitting the dynamic strength index of artificial structural loess with different D, rho d, and sigma 3. Our study outcomes can serve as references and guides for engineering construction in loess areas.

This study examines the dynamic shear strength properties of expanded polystyrene lightweight soil (EPS LWS) samples through dynamic triaxial tests, focusing on the effects of EPS bead content, cement concentration, and confining pressure. The results indicate that increasing the cement content positively correlates with the dynamic strength of EPS LWS due to the formation of reticulate cement hydrates that bond soil particles. When the cement content is below 10%, EPS beads have minimal impact on dynamic shear strength. However, at cement contents of 15% or higher, increasing EPS bead content reduces dynamic strength because the low-strength EPS beads break under these conditions. Elastic deformation in EPS LWS remains stable, with elastic strain increasing as EPS particle content and confining pressure rise. This highlights the significant impact of these factors on elastic strain, which is crucial for achieving the desired density and strength in engineering applications. The nonlinear behavior under dynamic stress and strain, showing strain hardening at critical levels. Higher EPS content reduces the dynamic stress required for bearing capacity due to decreased stiffness. Additionally, the dynamic elastic modulus increases with cyclic loading frequency, while higher confining pressure enhances hoop stress effects, requiring more dynamic stress to achieve the same strain. This study provides insights into the dynamic shear strength properties of EPS LWS, emphasizing the critical roles of cement content, EPS bead content, and confining pressure in influencing its performance in engineering applications.

Adding cement to soft soils may lead to brittle behavior and the occurrence of sudden damage. Methods to further improve the tensile and flexural properties of cemented clay are noteworthy topics. This paper mainly focuses on the effect of cement and moisture content on the strength and flexural properties of cemented clay reinforced by PVA fiber. The selected clayey soil was a kaolin with cement content of 5%, 10%, and 15% and moisture content of 50%, 56%, 63%, and 70%. The results show that the incorporation of 0.6% fiber can effectively improve the deformability of cemented clay in unconfined compression tests (UCS). The strengthening effect of fiber, as seen in the peak strength and post-peak strength of UCS, was significantly related to cement content. As the water content increased, the compressive strength of the fiber-reinforced cemented clay decreased, but its load-bearing capacity enhanced. When the cement content was 15%, the splitting tensile strength of fiber-reinforced cemented specimens increased by 11% compared to cemented soil, but the deformability of the specimens became poor. In the cement-content interval from 5% to 10%, the bending toughness was significantly improved. Sufficient cement addition ensures the enhancement of PVA fibers on strength and flexural properties of cement-stabilized clayey soil.

In order to identify the upper and lower boundary cement content for modified marine soft soil (i. e., semi-solidified soils), physical, compaction, and unconfined compressive strength tests of cement-treated soils with a wide range of cement content were carried out to study their variation law of physical-compaction-mechanical properties. The test results show that cement-treated soil can be divided into uselessly treated soil, semi-solidified soil, and solidified soil with the increase of cement content. For uselessly treated soil, the treated soil cannot be compacted even after compaction delay. Cement hydration in semi-solidified soil significantly improved its physical and compaction properties. However, compaction destroyed the skeleton structure of solidified soil, resulting in lower strength than compacted semi-solidified soil. Based on the cement-soil particles-water relationship, soil particles-water transfer mechanism, cement hydration mechanism and the state of soil particles-water before and after treated, the bound method of semi-solidified soils based on cement content and moisture content ratio of untreated soil was established. The test parameters of bound method are simple, easily obtained and have small dispersion, which provides design basis and theoretical support for resource utilization of marine soft soil.