Experimental study of seepage-scour failure in geotextile tubes gap with damaged vertical sidewall

Geotextile tubes, hydraulically filled with a slurry of fine silt and water, have been variously applied in hydraulic and coastal engineering fields. However, geotextile damage poses a great threat to structures made of geotextile tubes. When a water head difference exists across the tube, the soil in damaged tubes is affected by the dual actions of seepage and scour. To investigate soil failure patterns and tendencies of damaged tubes under hydraulic action, a structural apparatus and the corresponding test method were designed. Four factors considered were the radius of the damaged area (r0: 0.25-2.0 cm), the grain size distribution (Sand B Cu = 3.4, Sand E Cu = 50), the scouring flow velocity (v: 0-4 cm/s), and the hydraulic gradient. The results showed that the scouring flow exerted a limited effect on the failure mode of sand in the tubes, and that the failure process of sand in the tubes could be divided into three stages including a stable, an initial erosion, and a cyclic sand outflow stage. The hydraulic gradient at the initial erosion stage was defined as the critical gradient(jcr), which was interactively influenced by sand gradation, damage radius, and scouring flow velocity. Under identical conditions, Sand E exhibited a higher resistance against seepage-induced failure than Sand B. In terms of stability under varying conditions, for Sand B, increasing the damage radius (tested at flow velocities of 0-4 cm/s) reduced jcr by 94%-100%, while increasing the flow velocity (tested at damage radii of 0.25-2.0 cm) reduced jcr by 60%-100%. For Sand E, the corresponding reductions were 83%-95% and 58%-88%, respectively, further confirming Sand E's superior erosion resistance.