Abstract: The buoyancy characteristics of underground structures on sandstone foundation are studied for antifloating design and the seepage laws of groundwater are analyzed by indoor model tests and field monitoring tests. Results show that since sandstone is impervious, seepage condition, seepage pressure, and seepage time could all affect the buoyancy acting on sandstone structure, among which seepage condition has the largest impact. The influence of seepage pressure and seepage time on buoyancy changes with the variation of seepage condition. The buoyancy of underground structure on sandstone foundation can be reduced safely, and the reduction coefficient depends on the contact between basement and ground. The reduction coefficients in three contact conditions (simple contact, contact with sealing treatment in the peripheral and fractures inside the sandstone, and contact with sealing treatment in the peripheral and no fracture inside the sandstone) are 0.82-0.91, 0.63-0.73, 0.31-0.50, respectively. It is recommended to ease the antifloating requirements and adopt impermeable materials surrounding underground to alter seepage path and enhance reduction effect during foundation backfill.

Key words: sandstone foundation, buoyancy of underground structure, model test, field test, reduction coefficient