Installation-Induced Excess Pore Water Pressure and Post-Installation Axial Capacity of Jacked-In Piles in Vacuum-Preloaded Reclaimed Soft Soil

Coastal soft soils are characterized by high water content, high compressibility, and low strength, posing challenges for foundation engineering. In vacuum-preloaded reclaimed ground, jacked-in pile installation can generate excess pore water pressure and disturb the surrounding soil, thereby affecting post-installation pile behavior. Using the reclaimed soft soil foundation at the Taizhou Xingkong Flight School site as a case study, this study combines large-scale physical model tests with finite-element analyses to investigate pore water pressure evolution during vacuum preloading and the excess pore water pressure response around piles during jacked-in pile installation. Laboratory static load tests on single piles were further conducted to evaluate post-installation axial capacity under different installation conditions. Within the investigated jacking-rate range of 100–400 mm/min, the measured pore pressure increments did not exhibit a consistent monotonic dependence on jacking rate across all monitoring locations, and the available capacity results likewise showed no clear monotonic rate-dependent trend. At a jacking rate of 200 mm/min, the near-tip pore pressure increments increased from 17.54 to 22.71 and 25.77 kPa as the pile diameter increased from 60 to 80 and 100 mm, respectively, while the measured axial capacity also increased with pile diameter in the selected tests. Comparison between the physical tests and numerical simulations showed closer agreement at the shaft-side monitoring locations than near the pile tip. Because the numerical installation analysis represented only the final 10 mm of pile penetration, the numerical results are used primarily for the comparative interpretation of the responses under the investigated conditions. The results highlight the importance of considering monitoring location, pile geometry, and pore pressure dissipation when interpreting installation effects and post-installation pile behavior in vacuum-preloaded reclaimed soft soil.