Seismic Retrofit of Coastal Dikes

Soil liquefaction and associated ground failures have caused much damage to coastal and waterfront structures in the past major earthquakes. The prevalence of liquefaction in the coastal environment necessitates the development of appropriate remediation countermeasures. This paper presents an experimental study involving centrifuge physical modeling to assess the earthquake performance of countermeasure retrofit techniques for a liquefiable marine foundation under an existing coastal dike-embankment. Currently, such testing results offer a valuable alternative to studying actual full-scale dynamic response, since such data is virtually non-existent for retrofitted dikes. The response of a cohesive dike supported on a loose saturated sand layer is analyzed under dynamic base excitation conditions. In a series of four separate heavily instrumented model tests, this embankment foundation system was studied first without, and then with, the following three foundation liquefaction countermeasure-retrofit techniques: crushed gravel (drain) walls, cemented soil walls, and sheet-pile enclosure. The underlying mechanism and effectiveness of each countermeasure is discussed, based on the recorded dynamic response. All of the implemented countermeasures were found to significantly reduce embankment deformations. In some cases, cracking and lateral spreading of the dikes were practically eliminated.