Research on the influencing factors of the mechanical properties of metro jet system by full-scale test

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.