Flow mechanisms and permeability in stacked clay-filled soilbags: role of inter-layer gaps

Stacked soilbags filled with clayey soils are widely used protective measures in hydraulic and geotechnical engineering. The permeability of these soilbags is vital for the stability of earthworks, yet their hydraulic conductivity behavior remains inadequately characterized. To address this, this study investigates the performance and mechanisms of hydraulic conductivity in stacked soilbags. A series of large-scale permeability tests were conducted, considering factors such as flow direction, hydraulic gradient, stacked types, and gaps between bags. Results indicate that horizontal apparent hydraulic conductivity is significantly greater than the vertical coefficient. This allows infiltrating water to discharge rapidly along horizontal inter-layer gaps, preventing deep penetration into the underlying clayey soil slope. The permeability is primarily governed by the size of gaps between bags; the influence of stacking type is attributed to its alteration of gap quantity and geometry, which was further supported by numerical simulations. Furthermore, when inter-layer gaps are filled with soil, vertical apparent hydraulic conductivity remains unchanged, whereas the horizontal coefficient decreases significantly. Consequently, avoiding soil filling between gaps is beneficial for horizontal inter-layer drainage in practical engineering applications.