Analysis of the initiation criterion for sand fluidization induced by leakage from water supply pipelines under changing submerged water levels

Leakage from water supply pipelines can induce fluidization of overlying sand, leading to subsurface voids and ground subsidence. Most research focuses 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. An analytical formula is derived for the initiation flow rate of sand fluidization under varying submergence levels, based on the balance of sand's weight and seepage forces. Model tests validate this formula. Results show that reducing submergence levels, increasing sand particle size, and overburden depth decrease the initiation flow rate, while orifice size has minimal impact. The Ergun equation is empirically modified to better describe fluid pressure drop in sand under local pipeline leakage conditions.