# Effect of Plastic Fine Content on the Static Liquefaction Potential of Sandy Soil
## 4 Conclusions  
This study investigated the static liquefaction behavior of the Fontainebleau clean sand and the mixtures of this sand and the plastic fine Illite Arvel via undrained monotonic triaxial tests. Samples with fine content of up to 25% were reconstituted by using the moist damping technique. The effects of different parameters were studied, such as the fine content, the initial density index, the confining pressure, and the over-consolidation ratio (OCR). The test results were also compared to the Chinese criterion for liquefaction susceptibility to verify this criterion against the Fontainebleau sand. The following main conclusions can be made:  
* Clean sand at a very loose state (Idi = \(-\)0.2) exhibits a total collapse behavior even if for a high cell pressure (Pc = 400 kPa). * Clean sand at a loose state (Idei = 0.1) is liquefied for three confining pressures: Pc = 50 kPa (total collapse for this case), 100 kPa, and 500 kPa. * Clean sand samples prepared at a dense state (Idi = 0.4) are not liquefied at low confining pressure (Pc = 50 and 100 kPa) but present a limited liquefaction at high confining pressure Pc = 400 kPa. * Specimens with fine content of up to 25%, reconstituted at a loose state (Idi = 0.0 for 0, 5, 10, and 15% of fine content; and Idi = 0.2 for 15, 20, and 25% of fine content) are liquefied (for a confining pressure Pc = 100 kPa). * The fine content seems to present a threshold of \(\sim\)10-15%. Below this value, the liquefaction resistance increases with an increase in fine content. Beyond this value, an increase in fine content leads to a decrease in the unsaturated strength. This trend is different from test results reported in the literature. It emphasizes that the effect of fine content on different sands may be different. * The specimens with 15% fine content reconstituted at different initial density indexes from the loose state (Idi = 0.0) to the dense state (Idi = 0.6) are liquefied (for Pc = 100 kPa). This trend is quite different to that of the clean sand, where the samples are liquefied at a very loose or loose state but present a dilatant response at a dense state (Idi = 0.4). * The mixtures with 15% fine content and reconstituted at a dense state (Idi = 0.4) are liquefied (but not totally collapsed) for a range of confining pressure from 50 kPa to 400 kPa. The clean sand with Idi = 0.4 presents a limited liquefaction response under the confining pressure of 400 kPa. * An increase in OCR until a threshold leads to an increase in the liquefaction resistance. Clean sand and mixtures are liquefied at a normally consolidated state while presenting a limited liquefaction response at over the consolidated state (for samples with Idi = 0.2 and Pc = 100 kPa). * All the liquefied samples (both total collapse and limited liquefaction) reach the peak of deviatoric stress at an axial strain lower than 1%. Figure 17: Liquefaction susceptibility according to the Chinese criterion: (**a**) liquidity limit vs. fine content; (**b**) ratio water content/liquidity limit (Wc/LL) vs. fine content; and (**c**) plasticity index (PI) vs. Wc/LL. * The Chinese criterion of liquefaction susceptibility is not totally suitable for Fontainebleau's clean sand and its mixture with Illite Arvel plastic fines. The present experimental work shows many interesting results. Especially, the effect of fine content tendency is different from the previous observations in the literature. Moreover, the result's trend is also different between clean sand and its mixture with the plastic Illite Arvel fine content. However, to confirm the results described above, further tests should be completed, for instance, the effect of initial density index, initial global density index, and initial intergranular density index on mixtures with different fine contents (other than 15% fine content). Moreover, sand with similar characteristics to Fontainebleau sand should be also used to verify the tendency.