## 4 Liquefaction Mitigation Using Colloidal Silica Grout
### Field Tests for Soils Gruoted with CS  
Since the performance of CS in soil improvement and liquefaction mitigation has been verified by a series of element and model tests, it was also justified by a field test conducted by [PERSON] et al. (2007) [PERSON] et al. (2007). The test site here was within a Canadian liquefaction experiment site located in Richmond, British Columbia. The soil stratigraphic sequence at the test site is characterized by a sand and silty sand layer at the surface, overlain over a layer of silt and sandy silt, following a 10 m liquefiable layer of sand to silty sand, buried at a depth of 5-15 m [79]. At the treated area, eight injection wells were spaced equally around the perimeter of a 9 m-diameter circle, with an extraction well at the center. Two injection stages were used for the injection well to permeate CS into the soil layers buried at depths of 6.5-7.5 m and 7.5-8.5 m, respectively. An injection well is designed to inject more than 7000 L of CS at a concentration of 7%. As a matter of fact, since some malfunctions occurred during the injection process, only 45,000 L of diluted CS suspensions were finally injected in the field test. After the grouting injection was completed, two decks of Pentolite 50/50 explosives were installed at each injection well to create blast-induced liquefaction. At the untreated area adjacent to the treated one, eight similar wells were excavated as blast holes to accommodate explosives, as shown in Figure 25. Six survey lines extended from the center, and a total of 14 settlement measurements were taken along each ray. Excess pore pressure was monitored in the treated area. The excess pore pressure ratio \(R_{u}\) was adopted to indicate the evolutive law of pore water pressure. It was shown that \(R_{u}\) reached 1, even in the treated area, indicating the grouted layer can be considered to have liquified here. However, the settlement measurements indicate that a maximum settlement of 0.5 m was recorded in the untreated area, while the maximum settlement reduced to 0.3 m in the treated area (Figure 26). Moreover, [PERSON] et al. (2007) deduced that the 0.3 m deformation mainly occurred in the untreated layer, and the reduction in settlement should be attributed to the grouted layer (at depths of 6.5-8.5 m). They believed that the majority of settlement would be prevented if the entire layer was grouted. Figure 25: Site layout for full-scale test (modified after [PERSON] et al., 2007) [PERSON] et al. (2007). [PERSON] (2010) then performed another field test to investigate the mitigation effect of CS grouting on liquefaction damage [66]. In this field experiment, CS was grouted and transported to treat a 1.5 m-thick, poorly graded sand layer, with an area of 9.3 m\({}^{2}\). In the preliminary test layout, two kinds of grouting techniques, including mandrel injection and the well/packer injection method, were planned to be adopted to permeate CS to the targeted area. Furthermore, a TRex mobile shaker was intended to be used to induce liquefaction, and the targeted area was set hexagonally to match the shaker pad of the TRex shaker [66; 80]. However, two dominant difficulties were presented in the field. First of all, the mandrel injection method proved to be unsuccessful in practice. Secondly, the measured pore pressure response indicated no significant increases in pore water pressure in vibro-seismic shaking when using TRex shaker. Thus, it is uncertain whether the TRex shaker will produce remarkable shear strains and initiate liquefaction at greater depths. Therefore, the packer injection method was finally adopted, and mandrel replaced TRex mobile shaker to induce liquefaction. The mandrel was equipped with a vibratory hammer to supply the excitation.