Dynamic behavior of liquefiable ground reinforced by in-situ cement-mixing lattice wall

In-situ cement-mixing lattice-shaped ground improvement (lattice wall) is one of the effective countermeasures for liquefiable grounds. However, its high cost hinders its wide applicability. This is mainly due to the conventional concept of seismic designs which do not allow any liquefaction of the ground against earthquakes. The recent seismic design code was revised to comply with the concept of performance-based design, which allows some displacement or slight damage to structures, such as pile foundations, during major earthquakes. In order to apply lattice walls to meet the concept of the recent design standard, especially against major earthquakes, it is necessary to establish a rational design method that considers the quantitative effect of lattice walls. In this study, therefore, a series of 1-g field shaking table tests was performed with a lattice wall, and the effect of the wall was carefully evaluated through the quantitative measurement of the stress-strain relationship of the liquefiable ground inside the lattice wall and in the free ground (without a lattice wall). It became possible to quantitatively examine the effect of the wall by installing small accelerom-eters into the ground with precision. Two major positive effects of the lattice wall were observed through the series of shaking table tests. One was the delay in the onset of liquefaction by the restriction of shear strain, and the other was the recovery of the shear stiffness of the ground even after the onset of liquefaction. These experimental results indicate that lattice walls can be applied as an effective liquefaction countermeasure method, especially when the performance-based design is applied to address large earthquakes.