Liquefaction resistance of unsaturated sands: experimental evidence and theoretical interpretation

Abstract

Cyclic undrained triaxial tests were carried out on saturated and unsaturated loose specimens of three fine-grained materials. The results confirm that, as the saturation degree decreases, liquefaction resistance sharply increases. In the interpretation of results, the first step was the assessment of the reliability of the use of the 5% strain amplitude criterion to define the attainment of liquefaction. With this aim, the tests were analysed assuming that the soil behaves as an equivalent viscous material. It is shown that the characteristic values of viscosity defining the start and completion of liquefaction depend on soil grading, increasing as the coefficient of uniformity increases. The equivalent viscosity corresponding to a condition of double strain axial amplitude of 5% is fairly constant for all soils. Then, starting from the observation of the relationship between the final volumetric strain and the initial degree of saturation, a theoretical interpretation of the tests is reported. It is shown that the behaviour of the tested sands can be interpreted quantifying the thermodynamic specific energy spent to reach liquefaction, considering the contribution of all phases (soil, water and air). The position of the liquefaction resistance curve depends on the volumetric component of such a specific energy.

The effect of confinement in liquefaction tests carried out in a cyclic simple shear apparatus

“…Liquefaction occurs when the excess pore pressure ratio (Ru) is equal to 0.90 (stress criterion) or when shear strain in double amplitude is 5% (ϒDA). In saturated conditions these two criteria should give the same results as shown by [3] in triaxial conditions. In Table 2 is reported Nliq evaluated by strain criterion.…”

2nd Seminar on Transportation Geotechnics, Soil Improvement Challenges on Alluvial Zones

“…Soil Improvement Challenges on Alluvial Zones 2 nd Seminar on Transportation Geotechnics | 28-29 January 2019 | Vila Franca de Xira, Portugal 9 Figure 3. Volumetric strain vs number of cycles a sand with Sr= 55% and Sr= 87% (adapted, Mele et al 2018) It was proved that theoretical interpretation has conclused that this is consistent with the assumption that the cyclic resistance curve of unsaturated soils is a unique function of the volumetric component of the total specific energy spent to reach liquefaction.…”

“…the volumetric strain at which liquefaction is triggered): the liquefaction resistance of a partially saturated soil can be quantified from the one of the saturated soil by estimating the potential volumetric strain caused by the gas phase. Mele et al (2018) have presented laboratory experimental results that confirm that desaturation increases liquefaction resistance and defend that the change in behaviour of the soil after liquefaction is due to an apparent viscosity (Fig. s 3).…”

Electrolysis: An Innovative Technique to Desaturate Tailings

“…As well-known when the degree of saturation (Sr) increases, the resistance to liquefaction increases. Desaturation seems to be a useful remediation against liquefaction, especially in cyclic liquefaction as shown by several research works [1][2][3][4]. In fact, a small decrease in the degree of saturation of a fully saturated sand can result in a significant increase in shear strength against liquefaction.…”