Mechanism of settlement control of piled raft with gap or compressible block at pile top for support of railway embankment

Based on the experimental tests completed before, a concept of piled raft with gap or compressible block (PRGCB) at pile top is developed with conventional piled raft (CPR). PRGCB is expected to reduce post-construction settlement by using part of the embankment as preloading to consolidate the soils surrounding and beneath the piles. FEM simulation of the CFG piled composite ground of the Jing-Jin high speed railway is carried out first, and then piled raft with gap between pile head and raft is analyzed. The interaction between pile and soil and the development of settlement of piled raft with and without gap between pile head and raft are comparatively studied. Experimental tests and numerical results show that with the gap, soil may carry most of the load applied before pile head and raft get in contact. As a result, soils surrounding the upper part of the piles and beneath pile tips may be compacted before the piles start to carry significant load, and thus post-construction settlement may be reduced.