Gas can be found in many soils, but none more common than seabed soils. Gas-charged sediments are widely distributed throughout the world's oceans. Occurrences have been reported in coastal and estuarine regions, across the continental shelves, and deep within ocean basins. Recently documented cases have observed several submarine slopes known to contain methane gas, to experience flow or cyclic liquefaction.

Although gassy soil behavior has been studied by various researchers, the emphasis has been on fine grained soils or in some instances dense sands. There appears to be on published research work that studies the effect of gas on the behavior of loose sand. The objective of this thesis was to determine how the presence of gas affects the potential for flow and cyclic liquefaction.

In setting up the experimental facilities, a new method to measure gas content using a time domain reflectometry mini-probe was developed. Laboratory testing consisted of static and cyclic triaxial tests performed on saturated and gassy samples. Static test results showed that loosely prepared specimens with an initial degree of saturation greater than approximately 80% strain softened and experienced flow liquefaction, while loose specimens with an initial degree of saturation less than 80% were not susceptible to flow liquefaction. Cyclic triaxial test results showed that the resistance to cyclic liquefaction was increased by the presence of even a small amount of gas.

A constitutive model, developed at the University of Alberta that simulates the behavior of saturated loose sand samples was modified to account for the effects of gas. The modifications involved incorporating the increased compressibility of the soil as well as the equilibrium behavior of gas. The modified model captured the behavior of loose gassy sands subjected to static loading.

This research has shown that loose gassy sand can experience flow and cyclic liquefaction. The laboratory results indicate that the resistance to liquefaction increases with decreasing degree of saturation. Guidelines for determining the potential for flow and cyclic liquefaction are suggested. By integrating the laboratory and numerical work, an initial understanding of the effect of gas on the liquefaction potential of loose sands was developed.