Model tests on dynamic response of ballastless track X-shaped pile-raft foundation under long-term train loads

Based on a series of 1︰5 scale model tests on ballastless track X-shaped pile-raft foundation, the dynamic response of the foundation in saturated sand is studied under long-term train cyclic loading. The dynamic stress of the X-shaped pile, the skin friction of the pile and the cumulative settlement of the foundation with the number of loading cycles are analyzed. It is found that the axial force and cumulative settlement of the pile increase with the increasing loading cycles, but the rate of increment decreases. The axial force of the pile body is time-dependent. In addition, the lower the loading frequency, the lower the number of loading cycles required for the axial force of the pile to be stabilized. The area of negative friction is within 1 m from the top of the pile, and the area of positive friction is below 1 m from the surface. The neutral point is at 1/4 of the pile length. The variation rules of normalized axial force, side friction and settlement of the pile with the number of normalized loading cycles can be described by a logarithmic function.