Formulation of initiation criterion for sand fluidization induced by water supply pipe leakage under varying inundation levels

Leakage from water supply pipelines can induce fluidization of overlying sand, leading to subsurface voids and ground subsidence. Current experimental and theoretical studies generally focuse on continuously graded saturated sand, neglecting unsaturated and intermittently graded conditions. This study considers factors such as sand particle size, grading, pipeline submergence level, overburden depth, and leakage orifice size. Based on the balance of sand's weight and seepage forces, an analytical formula is derived for the initiation flow rate of sand fluidization under varying submergence levels, Model tests are used to validate this formula. Results show that reducing submergence levels, increasing sand particle size, and overburden depth will decrease the initiation flow rate, while orifice size has no significant impact. In additions considering the practical proposed situation that there is no fixed boundary for pipe lakeage and fludization of overlying sand, empirically modified the Ergun equation is to better describe fluid pressure drop in sand under local pipeline leakage conditions.