Foundation Liquefaction Countermeasures for Earth Embankments

Abstract

A centrifuge-testing program is conducted to assess the earthquake performance of countermeasure retrofit techniques for a liquefiable foundation under an existing embankment. Currently, such testing results offer a valuable alternative to actual full-scale dynamic response, which is virtually nonexistent for retrofitted embankments. The response of a cohesive highway embankment supported on a loose saturated sand layer is analyzed under dynamic base excitation conditions. In a series of five separate model tests, this embankment-foundation system is studied first without, and then with the following four different liquefaction countermeasure techniques: densification, cement deep-soil-mixing, gravel berms, and sheet-pile enclosure. The underlying mechanism and effectiveness of each countermeasure are discussed based on the recorded dynamic response. Effects of each countermeasure on both foundation excess pore pressures and embankment deformations are analyzed and compared. The implemented countermeasures are found to reduce embankment vertical deformations by a maximum of about 50%. However, in some cases cracking and lateral spreading of the embankment are practically eliminated. Thus, retrofit techniques that constrain lateral flow of the underlying liquefied soil are deemed to be particularly effective in preserving overall embankment integrity.