Downdrag Behavior of Piled Foundations Caused by Deep Water Pumping: A Forensic Study of a Damaged HSR Viaduct

One of the viaducts of the high speed railway in Taiwan has suffered significant structural cracks in its piers. This has raised serious public concern. The damage was conjectured to have resulted from ground settlement due to regional water pumping. The paper proposed a practical methodology to investigate the downdrag behavior of the pile foundations of the viaduct. A fictitious settlement controlled layer beneath the pile foundation was used to control the ground surface settlement due to deep water pumping. A three-dimensional finite difference mesh including the soil profile and the pile foundation was established with the geotechnical investigation report and design data. By varying the ground surface settlement, the variations of the pile settlement, ground settlement, and downdrag force with depth for each pile can be reasonably simulated. The results show an obvious pile group effect, which shows the minimum downdrag force in the interior pile and maximum force in the corner pile. There also exists a critical surface ground settlement at which the drag force reaches the maximum value. The simulated differential settlement was close to the measured value, however this was not enough to have caused the structural cracks in the piers. The cracks are more likely caused by other engineering events.