Field Investigation of Collapse of a 13-Story High-Rise Residential Building in Shanghai

In 2009, a 13-story residential building founded on lightly reinforced prestressed high-strength concrete (PHC) pipe piles in Shanghai collapsed completely during the excavation of an adjacent underground garage (i.e., on the southern side). In the course of construction, excavated soil had been dumped on the northern side of the building and formed a 10-m-high fill slope before the collapse. In order to identify the principal cause of the sudden building collapse, an extensive field investigation was carried out immediately after the accident. In addition to geotechnical exploration of soil properties, physical evidence was collected and documented including the layout of collapse debris, damage to piles, and induced pile movements. To assist in the investigation and provide insights into the collapse, three-dimensional finite-element analysis was carried out to simulate the process of excavation and dumping. For piles located adjacent to the dumped soil on the northern side of the building, uppermost fractures could be seen near the interface between the reinforced and unreinforced sections, which were located approximately 1–2 m below the original level of the pile head. Most of these failure surfaces were flat, implying that these piles failed under tension. For piles situated on the excavation (southern) side of the collapsed building, the uppermost fracture surfaces were tilted at an angle and the concrete was severely damaged, suggesting that these fractures occurred mainly from compression. Photographs of the pipe interior taken with a high-resolution digital camera and results of a low-strain pile integrity test revealed that most piles examined had generally broken into three or more sections. According to results of the numerical analysis, the largest bending moment was developed in the piles on the excavation side of the building at a depth corresponding to the interface of the soft and firm-stiff clay layers (13.5 m below the ground surface), under the combined effect of excavation and dumping. This suggests that the failure occurred first for piles on the excavation side, and eventually caused the building to fall flat onto the excavation site. A lesson learned from the accident is that geotechnical engineers and contractors should be better trained to improve their understanding of the effects of surcharge loading on PHC piles. Moreover, proper construction procedures and site supervision schemes should be explicitly spelled out and strictly followed by all parties during construction.