Load-sharing ratio of prebored and precast piles in piled-raft foundations socketed in weathered rock

The load sharing ratio of the prebored and precast pile in top-down method foundation was investigated by using a numerical analysis and a field case study. The emphasis was on quantifying the apparent load sharing ratio of the prebored and precast pile during the top-down method construction process. A series of 3D FE analysis were conducted with special attention given to the pile load sharing ratio under various conditions, such as pile geometry, pile length and structure load. In addition, the load sharing ratio of a single pile was also investigated based on the location of the pile in the raft (footing). The analysis model was verified by comparing the analysis model with the field data of an actual construction site using the prebored and precast pile and the top-down method. Based on the series of analysis results and the field measurements, when the soil condition is better than weathered rock and for moderate pile length, at least 15% of the total structure load was supported by the pile throughout the construction process. Furthermore, it was shown that the pile near the center of the raft carried more structure load compared to the piles in the side and the corner of the raft.