Mitigation of Nonuniform Settlement of Structures due to Seismic Liquefaction

Limited uniform settlement of a building subject to liquefaction may not affect the living conditions of the residents immediately after an earthquake. However, even some small nonuniform settlement can cause serious disruptions to residents' normal life. Because most residents of inexpensive houses cannot afford expensive retrofitting measures against this problem, different possible countermeasures against seismic nonuniform settlement of buildings are proposed, and their performance is evaluated in this study. The proposed mitigations should be not only technically promising but also economically affordable for residents of private houses. The proposed mitigations are (1)installation of sheet-pile walls around the building's foundation with limited lowering of the groundwater level; (2)installation of diagonal drains under the foundation accompanied by limited lowering of the groundwater level; and (3)limited surface ground improvement. The experimental results showed some differences between the performances of the proposed mitigations in non-uniformly loaded buildings compared with cases of uniformly loaded buildings. It is observed that installation of sheet-pile walls is not a promising countermeasure against tilting of the structures even though it reduces the total settlement. The liquefied sand in the area surrounded by the sheet piles and the building's foundation could easily deform, resulting in tilting of the building. In contrast, installation of drains reduced both settlement and tilting of structure by providing a nonliquefied column of soil under the foundation. Surface ground improvement also reduced both total settlement and tilting of the structure. However, its efficiency in reduction of the uniform settlement was found to be mostly dependent on the length of improvement rather than its depth, whereas the depth of improvement plays an important role in reduction of the tilting.