Effects of local scour and caisson geometry on the drag force of bridge foundations under steady flow

The local scour has not been well implemented in the calculation of drag force due to the difficulty in scour assessment of large bridge foundations. A numerical flume, including an independent flow-developing flume and a local scour flume, was developed to investigate the effects of local scour and caisson geometry on the drag force. The independent flow-developing flume was built to generate the actual inputting velocity profile for the local scour flume. The drag force was obtained using the hydrodynamic pressure from the local scour flume on the caisson. The developed numerical model was validated by the experimental tests of a caisson foundation. The effects of local scour, caisson size and skirt geometry on the drag force were investigated and discussed based on the numerical simulation of six models with different geometries. The following conclusions can be drawn: (1) local scour increases the drag force on the caisson, which can be two times that excluding the effect of local scour; (2) the increase of caisson size results in an increase of local scour and even more significant increase of drag force; and (3) adding skirt reduces scour depth and drag force, which can be enhanced by optimizing the skirt form.