Abstract: The underpass in the urban area has a trend of rapid development. But the impact of the underpass construction on the adjacent existing viaduct does not have a reliable evaluation method and the monitoring measurement during the construction is the only solution. After the review of the deformation criteria of the bridges, the deformation criteria of evaluating the impact of the underpass construction on the piers of the adjacent viaduct are discussed. These criteria have been verified during the construction.

Key words: Undercrossing Pass, Viaducts, Bridge Piers, Deformation Control Criteria