Bubble Growth and Release in Sediments during Water Level Drop: A Growth Model of Isolated Bubbles

Methane and other gases released from soft sediments are among the main sources of greenhouse gases in the atmosphere. In this paper, a growth model for isolated bubbles in the sediments was established based on the theory of linear elastic fracture mechanics. Water level drop experiments were conducted using magnesium lithium philip silicate transparent soils, and the changes in bubble pressure and morphology during water level drop were analyzed. The experimental results show that there is a critical pressure for bubble growth caused by a drop in water level. Bubbles only start to grow by fracturing the overlying sediments when the water level drops to the critical value because the critical bubble pressure is lower than the actual bubble pressure. The strength of soil, depth of the bubble position, longitudinal length of bubble, and amount and rate of water level drop are key factors affecting isolated bubble growth. Bubbles in the soils with higher strength are more difficult to reach the critical state but have a faster growth rate once they do reach it. The depth of bubble position only affects the time reaching the critical state and does not impact the post-growth process. Deeper bubbles are more difficult for initiating growth. For bubbles at the same depth, larger bubbles begin growing earlier. As bubbles become larger, the growth rate of the bubble increases progressively faster. Faster water level drops result in shorter times to reach their critical state and accelerate their growth rate.