Laboratory Investigation of the Effects of Blanket Defect Size on Initiation of Backward Erosion Piping

Backward erosion piping (BEP) is a leading cause of levee and dam failures and generally occurs when seepage flow breaks through a defect in the downstream low-permeability blanket layer, causing a shallow erosion channel to form and extend toward the seepage source. Unfortunately, to our best knowledge, limited research has been conducted on the effects of blanket defect properties (i.e., size or material properties) on BEP processes because of the existence of a preset exit in most experiments. In this study, a laboratory testing apparatus was designed and constructed to investigate BEP initiation with respect to the blanket defect size. During the BEP initiation process, three failure morphologies were identified within the samples: shear failure; bending failure; and bending–shear failure. The results indicated that the failure morphology and critical gradient were not only a function of the unit weight of the soil and water but also highly influenced by the geometrical proportions and thickness of the defects. The findings of this study identified measures that may be applied in the field for seepage protection against BEP.

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