Retrofit of Foundations Supporting Structures That Have Undergone Settlement Located in Seismically Active Zones

Reinforced cement concrete foundations undergo settlement and damage when there is an error in the design or in situations when the loads transferred to the foundations from the superstructure exceeds the supporting soil’s bearing capacity. Retrofitting of foundations is a challenging job when compared to retrofitting other structural members present in the superstructure. The work presented in this paper is a practical case of retrofit of a slab-type reinforced concrete raft foundation that supports a mercantile building founded on medium sand. The raft foundation has undergone settlement and deformation at few locations due to erroneous design and has previously experienced an earthquake. The settlement and damage that have taken place at various locations in the existing raft are assessed and retrofitting of the raft foundation is carried out by introducing new RC beams and RC jacketing of the raft. The new RC jacket comprises an additional new layer of concrete with reinforcement increasing the overall thickness of the raft slab. Parametric study carried out through analysis adopting finite element methods in ETABS, for different thickness of reinforced concrete jackets and depths of RC beams when the structure along with the retrofitted raft foundation is subjected to gravity and seismic loading. The structural effectiveness of the retrofit applied on the raft is assessed based on the respective optimum RC jacket thickness and depths of newly introduced reinforced concrete beams to check for any possible settlements in post-retrofit scenarios.