Failure and Remediation of an Embankment on Rigid Column-Improved Soft Soil: Case Study

The south extension line was constructed as a new part of the Xintai Expressway in Guangdong Province, China. The project required the construction of an embankment over soft soil with a thickness of up to approximately 14.0 m, and prestressed pipe pile was selected for reinforcing the soft soil foundation to increase bearing capacity and reduce settlement. Embankment sliding with a length of approximately 110 m and cracking with a length that exceeded 300 m occurred before the construction of the pavement structure. Field investigation and theoretical analysis results indicate that the safety factor of the overall stability calculated by the existing code methods is overly large, thereby resulting in large design pile spacing, low design bearing capacity provided by single pile, and excessive load shared by subsoil between piles. These results all cause the flow sliding of soft soil between the piles and the bending fracture of some piles. The revised density method can be used to check the stability of flow sliding, and the bending moment of piles should also be checked during the embankment design stage. In addition, perpendicularity deviation and poor joint quality of pile construction also contributed to the reduction of the bearing capacity of the pipe piles and the overall stability of embankment. Reconstruction of additional rigid piles and add pile after drilling holes are adopted in the sliding and cracking sections to reinforce the failed embankment, respectively. The remediation effect was validated by the measured excess pore water pressure, subgrade settlement, and horizontal displacement.

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