Tugun Bypass Tunnel is part of the 7 km long Tugun Bypass connecting Southeast Queensland and Northeast New South Wales in Australia. The tunnel is under an extended section of the Gold Coast Airport runway and is built with diaphragm walls using the cut and cover method. The tunnel portals are joined with depressed ramps constructed with cast-in-situ U-shape reinforced concrete structures within the sheetpile-supported excavated areas. The site is underlain by alluvial and estuarine deposits up to 35m depth with the groundwater table close to the surface. Due to the high groundwater table, the ramps are constantly subjected to floatation. Steel screw piles with a single helix at the pile tip are used to resist the uplift force from floatation. The design of these screw piles requires the considerations of tensile capacity and long term displacement. A semi-empirical method was adopted for the calculation of the tensile capacity of the pile, which was then confirmed by full scale in-situ pull-out tests. Three-dimensional numerical modelling was undertaken to investigate the serviceability conditions of the ramp when it is subjected to floatation.