In the seismic design of pile foundations, the safety of the pile is assessed by considering the inertial force during an earthquake and subgrade reaction as external forces against the pile. The amount of deformation of the pile must be limited to a small value to maintain the safety of the pile. In the event of a large earthquake, quay walls and seawalls are subjected to lateral spreading because of the influence of biased seaward earth pressure. The amount of lateral spreading is considerably larger than what can be expected in a typical pile seismic design and may reach several meters. In this study, loading experiments that reproduced lateral spreading were conducted to evaluate the lateral spreading pressure acting on a pile when considerably large lateral spreading occurred. The experiment results showed that lateral spreading pressure depended on the ratio of pile spacing to pile diameter while the peak value of lateral spreading pressure was larger than the one assumed in practical design.

An open-type wharf with a pneumatic caisson foundation has strong earthquake resistance because of its high foundation rigidity, but the existing practical earthquake resistant design methods for an open-type wharf have been established only for a wharf with a steel pipe pile foundation. To follow this design procedure may be appropriate, however, the difference in the rigidity of foundation between the two structural types should be considered. The authors conducted two-dimensional finite element earthquake response analyses, modelling both open-type wharves with pneumatic caissons and soil layers, and discussed their earthquake responses. The earthquake response of the wharf with pneumatic caissons was shown to be different from that on a steel pipe pile foundation. Design procedure for an open-type wharf with pneumatic caisson foundation was proposed.

An open-type wharf with a pneumatic caisson foundation has strong earthquake resistance because of its high rigidity. Construction of wharves with stronger seismic resistance and a larger planned depth is indispensable to accommodate ever-increasing larger vessels. Considering this trend and strong earthquake resistance, open-type wharves with a pneumatic caisson foundation will be widely applied in the future. Consequently, it is necessary to establish a practical design method of the wharf. Existing practical earthquake resistant design methods for an open-type wharf with a steel pipe pile foundation follow the below-mentioned procedure: (i) To calculate acceleration response spectra at the position of 1/β below the virtual ground surface by means of a one-dimensional earthquake response analysis of the ground. Here, the virtual ground surface means a 1/2 gradient face in between the slope and the seabed. β is a pile characteristic value; (ii) To calculate response acceleration corresponding to the natural period of the wharf. Here, the damping constant is 20%; (iii) To divide the response acceleration by gravity acceleration to obtain seismic coefficients; and (iv) To calculate inertial force using the seismic coefficients and verify the stability of the structure. To follow the design procedure described above may be appropriate. However, the difference in the rigidity of foundation between the two structural types should be considered. The authors conducted two-dimensional finite element earthquake response analyses, modelling both open-type wharves with pneumatic caissons and soil layers, and discussed their earthquake responses. As a result of this study, the earthquake response of the wharf with pneumatic caissons is different from that on a steel pipe pile foundation. The optimum evaluation positions of acceleration response spectra have proved to be foundation bottom levels, and the optimum damping constant for the evaluation of response acceleration to range from 5-20%.

No abstract

No abstract