Abstract: Limit research effort has been made to explore the mechanism and settlement of high-speed railway bridge above goaf. With the pile group foundation of Guanshandi bridge in Hefei-Fuzhou high-speed railway as a prototype, a model test is carried out. According to the similarity theory, the similarity constants are derived and the similarity model materials are produced; and then the model setup is made. Based on multistage loading tests, three types of data are achieved including the internal forces of piles, stresses of soil among piles and the settlements of pile, pile caps, roof of goaf, the behaviors of piles and soils among piles as well as the settlement of goaf roof are determined. It can be found that the influence of goaf on the bearing capacity of pile is inversely proportional to the load. For all model piles, no negative skin friction is found to occur along pile shaft; and the center of the distributed skin friction in goaf descends significantly compared to those of the conventional piles. There is a critical value for the uneven settlement of pile group above goaf. If the settlement exceeds the critical value, the uneven settlement will stop growing. In addition, according to the test results and theoretical analysis, the equations for calculating bearing capacity and settlement of pile group above goaf are proposed based on the current code.

Key words: high-speed railway, goaf, group piles foundation, model test, bearing capacity, settlement