Liquefaction Countermeasures Using Floating Grid-Form Soil Improvement for the Container Yard Located in Harbor Area-Paper

Paper

Pdf Summary

The study assessed floating grid-form soil improvement (FGFSI) as a liquefaction countermeasure for harbor container yards. Unlike conventional grid improvement, FGFSI uses shorter walls in the shallow part of the liquefiable soil, reducing the amount of treated ground and construction cost.<br /><br />Two dynamic centrifuge model tests simulated shaking from a Nankai Trough earthquake: one without countermeasures and one with 5 m-high grid walls installed 1.5–6.5 m below ground. The FGFSI test examined grid spacings of 6 m and 12 m. Containers were modeled above a 17.2 m-thick liquefiable layer, and container and ground settlements, acceleration, and excess pore pressure were measured.<br /><br />Average container settlement was 0.571 m without improvement, compared with 0.280 m for the 6 m grid and 0.358 m for the 12 m grid—49% and 63% of the untreated settlement, respectively. FGFSI also reduced variation in settlement among containers. With 6 m spacing, container and ground-surface settlements were nearly equal; with 12 m spacing, their difference was larger, indicating greater container subsidence.<br /><br />Measurements showed that FGFSI did not prevent liquefaction everywhere, particularly outside the areas supported by containers. However, container contact pressure increased effective stress beneath the containers and helped suppress liquefaction there. The closer grid spacing provided greater support and reduced settlement.<br /><br />The tests indicate that shallow FGFSI can mitigate container settlement during strong shaking, with closer grid spacing yielding better performance.

Keywords

floating grid-form soil improvement

FGFSI

liquefaction countermeasure

harbor container yard

dynamic centrifuge model

earthquake shaking

container settlement

grid spacing

excess pore pressure

ground improvement