Buoyancy effects on structures: A case study on the controlled lowering of a raised underground garage

In recent decades, the height of buildings and the number of basement floors has increased, especially in valuable urban locations. With the development of cities and the infrastructure essential for their operation, extensive underground construction is being carried out, including utility lines, subway tunnels etc. Water accumulation, fluctuating or high groundwater levels in the area of underground structures, due to various reasons, might cause structures, forming a closed volume, to move upwards. The excessive buoyancy problem, which arises, when necessary, precautions are not taken, is often overlooked by engineers. The negative effects of buoyancy on structures typically manifest as uplifts, settlements, or rotations. The state of structures damaged by excessive buoyancy must be thoroughly investigated to determine whether rehabilitation is possible or if the underground structure needs to be completely removed due to the infeasibility or cost inefficiency of its possible rehabilitation. This paper presents a methodology for addressing the state of structures affected by excessive buoyancy to find a suitable technological rehabilitation solution, supported by a case study. It demonstrates how inadequate design and execution of a single detail of a three-story underground garage resulted in its sudden elevation due to buoyancy. Through a thorough examination of the site, the state of the raised structure, the original project documentation, and basic safety check of anti-floating stability, rehabilitation procedure for the successful and controlled lowering of the underground garage was developed. • Construction of diaphragm walls or piles around an excavation site for underground structure can create a pool environment. • Water accumulation at the excavation site or along perimeter walls of underground structures can cause them to move upwards. • In submerged underground structures, severe effects of buoyancy can occur if precautions are not taken. • A methodology addressing excessive buoyancy in structures exploring feasible rehab solutions via a case study, is presented. • A thorough review of the site, structure, and documentation enabled the controlled lowering of the underground garage.