Abstract: Magnesium lithium phyllosilicate (MLPS) transparent soil is used to build a double-layered soil model with upper hard layer and lower soft layer. The gas source generated in the sedimentary layer is simulated by pinhole gas injection. Based on the image recognition technology, the experimental research on the morphology change of gas bubble and the uplift deformation of the upper soil in the process of gas accumulation in the formation is carried out. The results show that: (1) The gas presents different shapes in the process of gas bubble accumulation, and the time and morphology of the gas bubble breakthrough depend on the strength and height of the upper soil. (2) The changes of gas bubble morphology, volume and pressure can be roughly divided into two stages. At the first stage, the gas bubble volume and width increase linearly, while the gas bubble height decreases gradually due to the contraction of the bottom, and the gas pressure increases slowly. At the second stage, the increase of gas bubble width is slowed down, the expansion speed of gas bubble volume is accelerated, the height of gas bubble begins to increase significantly, and the gas bubble pressure decreases rapidly from the highest point. The uplift height and width of the upper soil increase significantly at the second stage. (3) The width and volume of the gas bubble before breakthrough and the uplift width and height of the upper soil have a good fitting relationship with the yield strength and the height of upper transparent soil. (4) The thin plate theory can reasonably explain the mechanism of upper soil deformation caused by gas accumulation, while the medium-to-thick plate theory is not applicable.

Key words: double-layered soils, magnesium lithium phyllosilicate (MLPS) transparent soil, gas injection test, gas accumulation and breakthrough, soil deformation