Performance of deep soft ground improved by straight-line vacuum combined with surcharge preloading: Case study

Traditional vacuum combined with surcharge preloading (TVSP) is commonly used for treating soft ground. However, the extensive use of sand as a horizontal drainage system poses a challenge due to its high demand for infrastructure construction and land reclamation. The straight-line vacuum combined with surcharge preloading (SVSP) is a technical improvement and innovation of the TVSP. It eliminates the sand cushion with the PVDs being directly connected to the vacuum pump through the main and branch pipes. This case presents the initial application of the SVSP for expressway ground treatment. The results indicate that the vacuum pressure in SVSP is 11 kPa greater than in TVSP. The SVSP induces a higher consolidation degree and higher settlement of soil ground. The higher vacuum pressure in the ground treated by SVSP also leads to a faster dissipation rate and a lower value of porewater pressure. Removing the sand cushion alters the boundary conditions for ground consolidation, leading to a lower consolidation degree for shallow ground than TVSP, and a higher consolidation degree for deep ground. The improvement depth progressively increases over time from the surface towards deeper layers. Additionally, the SVSP offers a cost saving of 20.1% compared to TVSP.