Reduction in Liquefaction Induced Settlement of River Levee by Enhancing Horizontal Stress with Sheet Piles

Abstract

In order to reduce liquefaction damage to river levees, remedial stiff zones are constructed below toes of levees to restrain lateral flow deformation of liquefied foundation soil under the levee. Sheet piling, among other ground improving techniques, is preferably employed especially in urban areas where houses are existing close to levees and workspace is limited. Settlement of levee becomes smaller if sheet piles with a higher flexural stiffness are used. However, it is often the case that settlement does not satisfy the design criteria even if steel pipe sheet-piles with very high stiffness are used. In this study, an innovative countermeasure method using sheet piles is proposed. In the proposed method, the horizontal earth pressure is enhanced with the help of elastic nature of sheet piles. This is achieved by inserting a wedge along the sheet piles to the levee side which deforms laterally the soil below the levee, increases horizontal earth pressures and reduce the liquefaction susceptibility. The effectiveness of introducing additional horizontal stress, hereafter termed as pre-stress in this study, was examined through centrifuge tests. In the tests, the amount of the horizontal stress increase and the affected zone were confirmed by conducting cone penetration tests at multiple locations before and after application of the pre-stress. Dynamic centrifuge tests were carried out on models with and without the pre-stress. It was found that the cone tip resistance increased not only in the vicinity of the sheet pile but at almost everywhere in the soil beneath a levee. Settlement of the levee decreased with increasing the introduced pre-stress, confirming the effectiveness of the method.