Mechanism and application of vacuum-surcharge preloading combined with prestressed pipe pile-geocell in deep soft foundation treatment of storage yard

A deep soft soil foundation treatment project of a storage yard in Zhuhai, China was studied. Traditional foundation treatment countermeasures cannot meet the requirements of this storage yard project, such as high bearing capacity and stability, high-standard post-construction settlement and differential settlement control, and rapid, efficient and cost-effective treatment of wide areas. A comprehensive solution was thus proposed where the vacuum-surcharge was used to preload the entire yard foundation, and the prestressed pipe piles in combination with geocell reinforcement were then used to treat the sacking areas and geogrid reinforcement to treat the stacker and reclaimer areas. The strengthening mechanism of this comprehensive treatment technology was investigated. It is found that the soil arching effect of reinforced soils on the top of pipe piles can effectively transfer the stress, and that the geocell reinforcement plays a role in restraining the pipe piles horizontally, coordinating the uneven settlements, and producing a remarked effect of flexible raft slabs in pile-raft foundation. Then the treatment performance was analyzed by using in-situ monitoring data of bearing capacity, settlement, and lateral displacement responses. The field data indicate that the solution of vacuum-surcharge preloading combined with prestressed pipe pile-geocell can greatly improve the bearing capacity of soft foundation, control the horizontal displacement of soft foundation and reduce differential settlement of soft foundation. Therefore, the engineering problems of excessive settlement and instability of the storage yard in soft foundation were solved effectively. The results could provide technical reference and guidance for similar projects in deep soft foundation treatment. © 2020, Central South University Press. All rights reserved.