Liquefaction Mitigation of Silty Sands Using Rammed Aggregate Piers Based on Blast-Induced Liquefaction Testing

To investigate the liquefaction mitigation capability of rammed aggregate piers (RAP) in silty sand, blast liquefaction testing was performed at a soil profile treated with a full-scale RAP group relative to an untreated soil profile. The RAP group consisted of 16 piers in a 4 x 4 arrangement at 2 m center-to-center spacing extending to a depth of 9.5 m. Blasting around the untreated area induced liquefaction (r(u) approximate to 1.0) from a 3 to 11 m depth, producing several large sand boils and causing a settlement of 10 cm. In contrast, the installation of the RAP group reduced excess pore water pressure (r(u )approximate to.1 0.75), eliminated sand ejecta, and reduced the average settlement to between 2 and 5 cm when subjected to the same blast charges. Although the liquefaction-induced settlement in the untreated area could be accurately estimated using an integrated cone penetration test (CPT)-based settlement approach, settlement in the RAP treated area was significantly overestimated with the same approach, even after considering RAP treatment-induced densification. Analyses indicate that settlement after RAP treatment could be successfully estimated from liquefaction-induced compression of the sand and RAP acting as a composite material. This test program identifies a mechanism that explains how the settlement was reduced for the RAP group despite the elevated r(u), values in the silty sands that are often difficult to improve with vibratory methods. (C) 2021 American Society of Civil Engineers.

Automated summary

The study compared the untreated area with a full-scale RAP group in silty sand to investigate the liquefaction mitigation capability of RAP. It was found that the use of RAP reduced settlement caused by liquefaction, although the same settlement estimation method resulted in overestimation in the RAP treated area.