# Static Liquefaction Assessment Combining Shear Wave Velocity, Peak Strength and Soil Grading
## 4 Liquefaction Assessment Based on Stiffness/Strength Parameters
### Effect of Soil Type  
It is known that soil liquefaction is mainly a function of the contractiveness of the soil, which is affected, in the first place, by relative density. Relative density, in turn, is affected by the grain size distribution, shape of the grains and specific gravity. For this case study, specific gravity was not an issue since most soils have similar values, except the gold tailings, which have a very distinct \(G_{s}\) value of 2.94. The challenge was to find a parameter that could take into account not only grain size distribution but also indirectly consider the shape of the grains. Ref. [48] studied the effect of soil grading on the undrained shear strength of sands, considering \(C_{U}\) as an effective parameter to control shear resistance only for pure sand samples. Instead, the aim of this research was to define a single parameter for any soil type. Following this study, the coefficient of uniformity (\(C_{U}\)) was found to be  
Figure 14: Normalized peak deviatoric stress versus normalized shear wave velocity—simplified procedure to evaluate static liquefaction [46].  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Material** & \(b\) & \(V_{S1}\)* \\ \hline Gold tailings & 3.0 & 170 \\ Osorio sand & 3.5 & 240 \\ Silt & 3.0 & 150 \\ Algeria sand & 2.8 & 205 \\ Coimbra sand & 2.8 & 215 \\ \hline \hline \end{tabular}
\end{table}
Table 10: \(V_{s1}\)* and b fitting values for Equation (4).  
the most suitable parameter to correlate with the proposed ratios, as shown in Figure 15. Despite not being directly related to particle shape, \(C_{U}\) can evaluate soil dispersion by considering particle diameter, which is highly related to potential fabric configuration. Following these studies, this research found the coefficient of uniformity to be a reliable measure of the liquefaction potential. Figure 15 illustrates the new approach for predicting soil liquefaction potential for any type of soil, using \(C_{U}\) as a soil identifier.  
In order to construct the graph in Figure 15, the correlations needed to be consistent for all the soils. For that, the adopted limiting \(V_{s0}/q_{peak}\) ratios were those between strain softening and strain hardening for finer soils (gold tailings, silt and mixture) and between true liquefaction and strain hardening for uniformly graded sands (Osorio sand, Argelia sand and Coimbra sand) since they typically do not exhibit strain softening, as summarized in Table 8. For the case of the mixture, the ratios provided were considered indicative due to the limited \(V_{S}\) measurements in the undrained compression triaxial tests carried out so far.  
Still, as with most correlations, this framework does have a limitation. According to this approach, soils with a better grading are likely to be more resistant to soil liquefaction. However, in the case of gap-graded specimens, which display a high \(C_{U}\) (similar to well-graded soils), the \(V_{s0}/q_{peak}\) ratio would be expected to be high due to the high liquefaction potential (e.g., [49]). This would go against the trend displayed in Figure 15. In any case, natural soils are generally not gap-graded.  
Although more data are needed to confirm this trend, these promising results suggest that the limiting boundary between liquefaction or strain softening and strain hardening defined in terms of the \(V_{s0}/q_{peak}\) ratio can be related grain size measured by the uniformity coefficient.