Polyurethane resin injection is a treatment being considered as a replacement for traditional methods of ground improvement. It has been used to re-level foundations and concrete slabs that have settled over time. Additional claimed benefits of the treatment have been noted recently, including improved factors of safety against soil liquefaction and reduced earthquake-induced settlements. To investigate the capability of the polyurethane resin injection treatment to mitigate liquefaction, two full-scale blast liquefaction tests were performed; one test was conducted in an improved panel (IP), an 8 m circular area treated with the polyurethane resin in a 1.2 m triangular grid from a depth of 1 to 6 m, and another test in an untreated 8 m circular area, the natural panel (NP). Each blast test was severe enough to produce liquefaction (ru ≈1.0) in the respective panel, with blast-induced settlements in the range of 70 to 80 mm. Despite similar levels of ground-surface settlement in the IP and NP, settlement within the top 6 m of the IP was about half that of the NP. A CPT-based predicted settlement for each panel was employed using the Zhang et al. (2002) methodology. Good correlation was found between the observed settlements and predicted settlements in both panels. Differential settlements across the panels were calculated based on ground-based lidar surveys, with a reduction of 42 to 49% between the IP and NP. The measured total and differential settlements following resin injection were at the bottom of the range observed in blast tests on a variety of shallow ground improvement methods conducted by the New Zealand Earthquake Commission in 2013. The persistence of the polyurethane resin injection ground improvement three years following its installation was indicated by the lasting increase of fundamental in situ test parameters. The results of the study indicate that resin injection is a viable method of ground improvement to reduce liquefaction-induced settlements by creating a stiffer surficial crust.

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 4x4 arrangement at 2 m center-to-center spacing extending to a depth of 9.5 m. Blasting around the untreated area induced liquefaction (ru ≈1.0) from 3 m to 11 m depth, producing several large sand boils, and causing settlement of 10 cm. In contrast, installation of the RAP group reduced excess pore water pressure (ru ≈0.75), eliminated sand ejecta, and reduced average settlement to between 2 to 5 cm when subjected to the same blast charges. Although the liquefaction-induced settlement in the untreated area could be accurately estimated using the CPT-based settlement approach proposed by Zhang et al. (2002), 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 elastic compression of the sand and RAP acting as a composite material. The composite reinforced soil mass, surrounded by liquefied soil, transferred load to the base of the RAP group inducing settlement in the non-liquefied sand below the group. This test program identifies a mechanism that explains how settlement was reduced for the RAP group despite the elevated ru values in the silty sands that are often difficult to improve with vibratory methods.