Experimental and Momentum Analysis of Double-Layered Sand Fluidization Induced by Localized Seepage

Leakage from pressurized water pipelines leading to sand soil fluidization is a major cause of subsurface cavities and ground subsidence. Existing research focuses on single-layered sand, with limited studies on layered sand. This study investigates water pipeline leakage-induced fluidization in double-layered sand, analyzing the effects of particle size, thickness, and position of the layers. A theoretical model for fluidization cavity expansion is developed, and formulas for stable cavity shape and complete fluidization flow rate are derived. Results show that a jump-layer fluidization phenomenon occurs when the lower layer is coarse sand and the upper layer is fine sand. Fluidization initiation is controlled by the static balance between seepage force and soil weight, while complete fluidization is marked by surge failure under jet impact. The flow rate for fluidization initiation is controlled by the lower sand layer, and increasing its particle size raises the flow rate threshold. The complete fluidization flow rate depends on the sand bed's overall permeability, with particle size increase in either layer delaying complete fluidization. This study provides a theoretical basis for erosion prevention in layered sandy soils under pipeline leakage conditions.