双层地基中气体聚集与土体变形机制的试验研究

Experimental study on the mechanism of gas accumulation and soil deformation in double-layered soil

采用层状硅酸镁锂(magnesium lithium phyllosilicate,简称MLPS)透明土构建了上硬下软的双层地基模型,通过针孔注气来模拟沉积层中产生的气源,基于图像识别技术开展了地层气体聚集过程中气囊形态变化以及上层土体隆起变形的试验研究。结果表明:(1)气体在聚集过程中呈现出不同的气囊形态,上层土体的强度和高度决定了气囊突破的时间以及突破时的形态。(2)气囊形态、体积和压力的变化大致可分为两个阶段,第一阶段气囊体积、宽度基本呈线性增大,而气囊高度则由于底部收缩而逐渐减小,气压缓慢增大;第二阶段气囊宽度增加放慢,气囊体积膨胀速度加快,而气囊高度开始显著增加,气囊气压由最高点迅速降低。上层土体隆起的高度和宽度在第二阶段才开始明显增大。(3)气囊突破前的宽度、体积以及上层土体隆起宽度和高度与上层透明土的屈服强度、高度具有良好的拟合关系。(4)薄板理论可较合理地解释气体聚集引起的上层土体变形的机制,而中厚板理论则并不适用。

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.