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

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