For predicting the leak location in underground gas pipeline and preventing leakage accident, it is extremely important to study the diffusion behavior of gases in the soil by experimental method. With full-scale gas leakage experiments to simulate real underground pipelines, the tendency that gas spreads due to convection and diffusion in soil particles was investigated. Based on self-developed gas detection and data acquisition systems and GasClam in-situ borehole gas monitor, the convection-diffusion law of leaked gas in the soil was analysed. The experimental Tesults showed that the gas leakage in the soil can be divided into four stages, which are the embryonic stage, the high-speed growth stage, the low-speed growth stage, and stable phase. Variation of concentration of methane in soil with leak time was basically in accord with an"S"curve. The relation between time for gas concentration to reach detectable level at measuring point and distance from the leak site can be expressed with the power function equation. When the measuring point is located in the vicinity of the leak site, the pressure of underground gas pipeline plays a dominant role to diffusion of leaked gas. When the measuring point is located away from the leak site, so does the leakage quantity.%天然气在土壤中扩散行为的实验研究对埋地管道泄漏点的科学定位及泄漏事故的预防具有重要意义.采用全尺度气体泄漏实验系统,模拟真实埋地管道泄漏场景,对泄漏后的天然气在土壤中的扩散对流过程进行实验研究.基于自行研制的气体检测与数据采集系统和GasClam地下气体在线监测仪,分析天然气在土壤中的对流扩散规律.结果表明:埋地管道泄漏后天然气在土壤中的对流扩散过程可以分为4个阶段:孕育阶段、陡然增长阶段、缓慢增长阶段和稳定阶段,其浓度随泄漏时间的变化过程符合S型曲线特征.天然气扩散至检测点所需时间与距泄漏口距离呈现近似的幂指数关系.当检测点位于泄漏口附近区域时,泄漏压力起主导作用.当检测点位于远离泄漏口区域时,泄漏量起主导作用.
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