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.

With the gradual development of urban construction, more high-rise buildings with deep foundations are been constructed near tunnel groups. Analyzing how tunnels and surrounding strata respond to diverse construction strategies and challenging conditions during the excavation is crucial. This examination is instrumental in safeguarding infrastructure and minimizing construction expense. This paper explores the deformation response of structures and ground caused by irregular deep foundation pits that are excavated in structural strata adjacent to a tunnel groups (<5 m), as well as the effect of displacement control through grouting rectification techniques and Metro Jet System (MJS) isolation piles. Firstly, a finite element (FE) model is established to investigate the effects of MJS geometric and mechanical properties on deformation response for tunnels and surroundings. Then, an evaluation of the disturbance of underlying structural strata of the site is carried out to analyze the impact on deformation response. Finally, the displacement control effect of rectification technology is analyzed through a case of adjacent excavation. The results indicate that: (1) Strengthening the geometric and physical properties of MJS piles within a certain range positively contributes to deformation reduction. Additionally, increasing the length of MJS piles preferentially with the same amount of mud improves displacement control more effectively; (2) Increased soil disturbance weakens its structural integrity, amplifying the impact of excavation on structures and surroundings; (3) Employing rectification techniques proves effective in preventing excessive tunnel deformation. This study offers valuable insights for design and construction of deep excavation projects adjacent to tunnel groups.