Braced excavation systems are commonly required to ensure stability in the construction of basements for shopping malls and underground transportation facilities. For excavations in deposits of soft clays, stiff retaining wall systems such as diaphragm walls help to restrain ground movements and wall deflections in order to prevent damage to nearby buildings and utilities. The ground surface settlement behind the excavation is closely associated with the magnitude of basal heave and the wall deflections and is influenced by the possible ground water drawdown. This paper numerically investigates the influences of excavation geometries, the system stiffness, the soil properties and water drawdown on ground surface settlement and develops a simplified maximum surface settlement model. Considering the uncertainties of the design parameters, a probabilistic framework combining the estimation model with First-order Reliability Method (FORM) is proposed to determine the probability that a threshold surface settlement is exceeded.