Cyclic liquefaction of loose gassy sand

Abstract

Gas can be found in many soils, but none more common than in seabed soils. Gas-charged sediments are known to be widely distributed throughout the world's oceans. Numerous research programs have studied saturated soil response to cyclic loading; however, little is known about the behavior of gassy soils subjected to cyclic loading. The response of loose gassy specimens subjected to cyclic loading was studied in a laboratory program. Triaxial tests were performed on specimens of reconstituted Ottawa sand prepared to various gas contents and densities. The specimens were consolidated and then sheared under undrained cyclic loading. Gas content was measured at the beginning and end of each test using time domain reflectometry. The response of the gassy specimens has been shown to be influenced by the soil state and grain characteristics and the intensity, duration, and frequency of the cyclic loading. The propensity of a soil to liquefy is represented by a cyclic resistance ratio, defined as the cyclic stress ratio to cause liquefaction, or to cause a specified amount of strain. The results of this laboratory program show that the cyclic resistance ratio increases as gas content and density increase. The laboratory study demonstrates that the cyclic liquefaction potential of a soil is reduced by the addition of gas; however, soils containing some gas may still experience cyclic liquefaction provided they are sufficiently loose.Résumé : L'on peut trouver du gaz dans plusieurs sols, mais jamais aussi communément que dans les sols des lits de mer. Les sédiments chargés de gaz sont reconnus pour être largement répartis à travers les océans du monde. De nombreux programmes de recherche ont étudié la réponse du sol saturé à des chargements cycliques; cependant, l'on connaît très peu le comportement des sols gazeux soumis à un chargement cyclique. La réponse de spécimens gazeux lâches soumis à un chargement cyclique a été étudiée dans un programme de laboratoire. Des essais triaxiaux ont été réalisés sur des spécimens reconstituées de sable d'Ottawa préparés à différentes teneurs en gaz et densités. Les spécimens ont été consolidés et ensuite cisaillés non drainés sous des charges cycliques. La teneur en gaz a été mesurée au commencement et à la fin de chaque essai au moyen de la sonde d'humidité TDR. Il a été démontré que les spécimens gazeux sont influencés par l'état du sol et les caractéristiques des grains, et par l'intensité, la durée, et la fréquence des cycles de chargement. La propension d'un sol à se liquéfier est représentée par un rapport de résistance cyclique, défini comme le rapport de contraintes cycliques causant la liquéfaction, ou causant une quantité donnée de déformation. Les résultats de ce programme de laboratoire montrent que le rapport de résistance cyclique augmente lorsque la teneur en gaz et la densité augmentent. L'étude en laboratoire démontre que le potentiel de liquéfaction cyclique d'un sol est réduit par l'addition de gaz; cependant, les sols contenant du gaz peuvent encore atteindre la li...

Liquefaction of Unsaturated Sand Considering the Pore Air Pressure and Volume Compressibility of the Soil Particle Skeleton

“…According to the past studies (e.g., Yoshimi et. al., 1989;Grozic et al, 1999), when the pore pressure coe‹cient B-value drops to zero level, the degree of saturation decreases by about 90z. Also in this research, the pore pressure coe‹cient Bvalues before cyclic shear were very small in comparison with the full saturation case shown in Table 1.…”

Analysis of liquefaction susceptibility of nearly saturated sands

“…Therefore, due to high compressibility of the pore fluid, the amount of seismically induced excess pore pressure in a partially saturated soil can be significantly lower than that induced in the same soil at full saturation. This increase in liquefaction strength due to incomplete saturation has been proven experimentally [1][2][3][4][5]. For instance, cyclic triaxial tests conducted on Ottawa sand samples [1,2] confirmed that the presence of gas in partially saturated soils could enhance the liquefaction resistance of the soil samples expressed in terms of cyclic resistance ratio (CRR) by 200-300%.…”

“…This increase in liquefaction strength due to incomplete saturation has been proven experimentally [1][2][3][4][5]. For instance, cyclic triaxial tests conducted on Ottawa sand samples [1,2] confirmed that the presence of gas in partially saturated soils could enhance the liquefaction resistance of the soil samples expressed in terms of cyclic resistance ratio (CRR) by 200-300%. Other researchers have obtained similar results for the soil resistance against liquefaction due to partial saturation [3][4][5].…”

“…U a V a =CONSTANT. In Equation (2) x is the mole fraction of the dissolved gas in a liquid at equilibrium condition (i.e. related to the maximum dissolvable mass of the gas phase estimated by the Henry's law at the corresponding absolute pressure), and H is the Henry's constant, dependent on temperature.…”

A Review of Gassy Sediments: Mechanical Property, Disaster Simulation and In-Situ Test

“…Their main components include methane, carbon dioxide, and nitrogen (Figure 2). The gases mostly exist in the pores as dissolved or discrete bubbles (Wheeler, 1986;Grozic et al, 2000;Sánchez et al, 2017).…”