# Effect of Micropiles on Clean Sand Liquefaction Risk Based on CPT and SPT
## 3 Discussion and Results
### Results  
The degree of effectiveness of jet grouting using micropiles to mitigate liquefaction risk is a significant factor to be studied. This degree measures the efficacy of soil improvement by micropiles, as well as its practical merits. This section aimed to gauge the effectiveness of the soil improvement by micropiles based on the changes in the factor of safety. Comparisons of three CPT-based methods, along with three SPT-based approaches, for the prediction of soil strength after jet grouting against liquefaction risk, are presented herein. Table 3 demonstrates the effectiveness of soil improvement following CPT-based Boulanger and Idriss, Eurocode, and Juang methods. The effectiveness is evaluated based on four criteria from the smallest to the greatest improvement of the factor of safety. Criterion C-1 is defined as \(0<FS\leq 0.5\). In addition, C-2, and C-3 criteria indicate \(0.5<FS\leq 1\) and \(1<FS\leq 2\), respectively. The \(FS>2\) is categorized as the C-4 criterion, as the most effective degree of soil improvement. According to Table 3, the CPT-based Juang method reports the most stringent changes of the factor of safety in SP soil (34.4%), as shown in the C-4 criterion. It includes 11 cases out of 32 evaluated SP layers in five boreholes of site I. The C-1 criterion for clean sand using Boulanger and Idriss and Eurocode methods are comparable, but show the least improvement of the SP soil, which, respectively, belongs to 50 and 53.1% of the total SP layers. The C-2 criterion highlights the most comparable FS improvements in the SP soil according to the three CPT-based methods. Only 19% of the soil layers in site I is categorized as fine-grained soil; however, the CPT-based FS analysis results are presented. In this soil, the C-1 criterion had the highest percentages of cases compared to other criteria, which were, respectively, measured as (66.7, 83.3 and 38.9) according to the three methods. Inclusion of the highest case numbers in the C-1 criterion, as the lowest range of improvement for the fine-grained soil, is due to its low porosity characteristic compared to the SP soil.  
Table 4 illustrates the effectiveness of the soil remediation by micropiles following the SPT-based Boulanger and Idriss, Eurocode, and NCEER approaches. The same C-1 to C-4 criteria was used to measure the effectiveness based on the range of FS values after micropile installation and jet grouting.  
Figure 12: Improvement of the factor of safety against liquefaction triggering based on SPT, before and after jet grouting using micropiles in soil layers containing only poorly graded sand (clean sand).  
The most considerable improvement of FS for the SP soil (35.5%) was recorded in the C-4 criterion following both the Boulanger and Idriss and NCEER methods. It is shown that the FS improved dramatically from the C-2 to C-4, as there was no recorded case in the C-3 criteria, based on all three SPT-based methods or in both coarse-grained and fine-grained soil layers of site 2. Almost 24% of the soil layers in site II were fine-grained soil. Similar to the CPT-based results, the highest number of the fine-grained soil cases fit into the C-1 criterion.