A Study on Excavation-Induced Surface Settlement Due to Construction of Underground Station Box

Construction of an underground metro station box is a deep excavation problem. Ground deformations are inevitable in any deep excavation project due to deflection of retaining wall, dewatering and surcharge. Such ground deformations can affect the serviceability of adjoining over ground structures and underground structures or utilities. In cases of severe surface settlement, safety of such adjoining structures may also be at risk. Several researchers have attempted to predict excavation-induced surface settlement using empirical, analytical and numerical methods. In this paper, the applicability of empirical methods of surface settlement predictions due to braced excavation has been studied. Surface settlement has been predicted considering in-situ soil stratification, retaining structure, depth and width of excavations and factor of safety against basal heave. During construction of station box, surface settlement adjoining the zone of excavation is measured using surface settlement monitoring points. The empirical predictions have been compared with field data from one of the station boxes of Kolkata East West Metro project. The predicted surface settlement agreed reasonably well with observed instrumentation data.