Response of open-ended piles in sand to simulated earthquake and seaquake

During a simulated earthquake, horizontal motion caused about 20% permanent reductions in both the total axial compressive pile resistance and the plu g resistance in an open-ended model steel pipe pile. The loss of capacity w as primarily caused by a reduction of bearing capacity at the pile toe. But vertical motion resulted in no loss of pile or plug resistance. Plug failu re was not observed in any horizontal or vertical shaking test. During a si mulated seaquake, due to the induced excess pore water pressure and pressur e gradients in the soil, the capacity of short ( less than or similar to 27 m) open-ended single pipe piles installed in a simulated seadepth of great er than 220 m was reduced severely and the soil plugging resistance was deg raded by more than 80%. The soil plug failed because of the upward seepage forces that developed in the soil plug due to excess pore water pressure pr oduced in the bottom of the soil plug during the seaquake. The compressive capacity of short open-ended single piles in a simulated seadepth of less t han 220 m was reduced only by about 10%, and the soil plug resistance was d egraded by less than 5%. But the compressive capacity of an open-ended pipe pile with greater penetration (greater than or similar to 27 m) was not de graded, even in sea deeper than 220 m, and the soil plug within the open-en ded pile installed in a simulated deep sea was stable after seaquake motion . In the case of the 2-pile or 4-pile groups, the compressive capacity afte r seaquake motion was not degraded at all regardless of pile penetration de pth beneath the seabed, seawater depth or seaquake frequency.