Unwelcome settlers

The caissons at Port Island and Maya terminal have settled be­tween 0.7m and 3m and rotated up to 3 deg, says Liftech, which has caused the crane rails to spread. The tops of the waterside rail gird­ers are submerged in places and the fill adjacent to the caissons has dropped an additional 2-3m.

The cranes with a 50ft gauge have their landside rail girders sup­ported on steel piles. These have not settled appreciably but have rotated 3-5 deg in places. The cranes with a 100ft gauge have their landside rail girders on grade beams over engineered fill and these have settled in places. The crane rail girders have spread 1-2m at Port Island and 4-5m at Rokko Island.

Crane damage varies at differ­ent locations. A large number have significant structural damage and could collapse in the event of a strong aftershock. According to Liftech, the damage to the cranes is primarily due to the rails spread­ing and settling.

That is, it is as if the cranes were trying to “do the splits” as the quays separated and they are buckled at the portal ties. Liftech recommends that cranes are built with movement and rotation re­sistant ductile frames with heavy portal ties.The three MHI cranes at the APL terminal on Port Is­land (PC 5) were designed by Liftech and reportedly stood up well to the earthquake.

Liftech adds, however, that if the Guam earthquake of 1993 is anything to go by, it will take several months for the ground to solidify. This could cause further problems in the event of aftershocks.

The pile-supported dock structure performed well, while the caissons settled and rotated out.

Liquefaction caused the fill within the settled caissons to settle about 3ft.