Morphological Characteristics of Overlying Soil Eroded by Leakage Gas from Buried Pipelines

After an underground gas pipeline experiences damage in the form of microfissures, the pressurized gas has an erosion effect on the overlying soil, which will change the form of overlying soil and cause local displacement inside the soil. In serious cases, surface collapse accidents will occur. However, the current research on erosion caused by gas leakage remains lacking. The two-dimensional visualization of a buried pipeline leakage test device was used to perform gas leakage experiments at five gas pressures of 0.2, 0.3, 0.4, 0.5, and 0.6 MPa to fill the current research gap. Three soil moisture content levels of 0%, 5%, and 10% were set in the experiments. The process and morphological characteristics of soil erosion induced by gas leakage were obtained via image monitoring and processing. Results showed that after the leakage of the buried pipeline, the overlying soil was eroded by pressurized gas, and the overlying soil presented five processes: porosity, pore formation, erosion loosening, erosion expansion, and cyclic erosion. Soil within the erosion range can be divided into three typical areas in accordance with morphological characteristics: (1) the hole area, (2) the main fissure expansion area, and (3) the fully developed microfissure area. When the gas pressure was increased from 0.2 to 0.6 MPa, the nucleation volume of the hole increased by 3-4.9 times. When the soil moisture content was increased from 0% to 10%, the hole nucleation volume decreased by 50%-66%. The erosion fissures showed obvious fractal characteristics. When the gas pressure was increased from 0.2 to 0.6 MPa, the average fractal dimension of erosion fissures increased by 7.4%. When the soil moisture content was increased from 0% to 10%, the mean fractal dimension of erosion fissures decreased by 16.4%. That is, the formation and distribution complexity of erosion fissures increased with high gas pressure and low soil moisture.