Micro-disturbance grouting: soil and bridge substructure responses and pore pressure analysis using in situ tests and DEM simulations

This study investigates the effects of micro-disturbance grouting on highly sensitive silt and bridge substructures through in-situ tests, theoretical analysis, and numerical simulation. A calculation method for the average volumetric strain of silt is proposed based on cavity expansion theory, and the residual displacement differences between soils and structures are interpreted. The results indicate that larger grout volumes enhance soil consolidation and reduce post-grouting displacement of both soil and bridge piers, whereas smaller volumes result in greater residual deformation. By analyzing soil responses with the effective stress principle, the displacement evolution of soils and piers can be interpreted as a three-stage process, with post-grouting displacement governed by the relationship among effective stress, pore pressure, and soil pressure. Furthermore, fluid–solid coupled discrete element simulations reveal that pore pressure in sandy soils stabilizes rapidly with distance from the injection point, while silt exhibit a cumulative effect and require longer to reach peak values. The findings provide valuable references for the design and construction of similar engineering projects.