Difference of seismic behavior of high and low caps of pile foundations

The pile foundation could be classified into the high or low types according to the position of cap relative to the surface of grounds. In many engineering practice, the settlement of unconsolidated clay or backfilled soil after construction, the soil rheology or the seismic field subsidence may lead to the separation of the cap from the clay surface, i.e., the cap was embedded originally into clay to a new state of high cap pile foundation. For the static condition, this kind of separation may result in the negative skin friction force along the piles and reduce the vertical bearing capacity of piles. However, under the seismic shaking condition, the centrifuge shaking table experiments and simulation with ABAQUS on both the cases indicated that piles underwent a higher maximum bending moment and a much larger active depth under high cap case than those at low cap case. This suggested that the embedding condition played an important role in the seismic response of pile-cap foundation. It becomes more disadvantageous when the embedding condition of the cap changes from the low cap case to the high cap case. ©, 2015, Academia Sinica. All right reserved.