# Experimental and Empirical Studies to Evaluate Liquefaction Resistance of Partially Saturated Sands
## 6 Conclusions and Recommendations  
Studies on the cyclic behavior of induced partially saturated sands are limited. Current design practices are mostly based on the methods developed for nearly/fully saturated soils, but these are unable to consider the effects of the presence of gas bubbles in soils. This study was intended to provide experimental insights into the testing parameters that affect the liquefaction behavior of partially saturated sands with occluded gas bubbles. Moreover, this study proposed an alternative and potentially simple empirical methodology in which the liquefaction-resistance ratios were related in a unique way to the bulk modulus, maximum volumetric strains, and excess pore-pressure ratios. In this regard, a series of undrained dynamic triaxial tests were conducted on nearly/fully saturated and partially saturated sand specimens. The loose and dense specimens were reconstituted using the air-pluviation and dry-tamping methods. The partially saturated sands were prepared by percolating a sodium percarbonate-water solution through the specimens. The effects of four different testing parameters (namely, the degree of saturation, effective confining stress, back pressure, and relative density) were discussed with the aid of liquefaction-resistance curves. The validity and applicability of the proposed empirical approach were evaluated using the test results from the current study and the existing literature. The following conclusions were drawn:  
1. The liquefaction behavior of sand was observed to change as the triaxial specimens were turned from nearly/fully saturated to a partially saturated state. The liquefaction resistance of the partially saturated sand specimens appeared to increase as the degree of saturation was reduced. 2. The undrained cyclic behavior of the partially saturated sand was not only sensitive to the degree of saturation but also to the level of the initial effective confining stress and back pressure (or initial pore water pressure) acting on the sand. At the same degrees of saturation, the partially saturated sands showed a greater resistance to liquefaction under larger initial effective confining stresses and lower back pressures. Figure 17: Validation of the predictions against centrifuge [65] and 1 g shaking table [66] test data. Amongst these parameters, the effect of the back pressure was less significant than those of the degrees of saturation and confining stress. 3. The positive effect of the confining stress and the adverse effect of the back pressure require consideration in design practice. During the practical application of IPS methods for the treatment of liquefiable deposits in the field, the shallower layers should be desaturated more than the deeper layers. 4. The proposed empirical approach was shown to enable a practical assessment of the normalized liquefaction resistance of partially saturated sands as a function of the pore-fluid bulk modulus, maximum volumetric strains, and normalized excess pore-pressure ratios. The model seemed to successfully capture the trends followed by the experimental data and produced physically sensible estimations for a complex topic of geotechnical earthquake engineering. This study provided additional data and valuable insights that may enhance the scientific understanding of partially saturated soil behavior and the practical use of this particular IPS method in engineering projects. The experimental observations and empirical analysis were valid only for submerged, partially saturated clean sand specimens with occluded gas bubbles in which the effect of the matric suction was insignificant. Future studies should focus on sand deposits that contain some amount of salts and/or clays, and the robustness of the proposed methodology should be tested for different types of soils tested under a wider range of relative densities, degrees of saturation, and stress levels. This research received no external funding. Not applicable. The data presented in this study are available from the author upon reasonable request.