Abstract: Soil piping is one of the main causes of instability and failure in hydraulic engineering. To date, most of the existing studies on soil piping ignored the shape effect of sand particles; The seepage deformation results of some real projects are inconsistent with the theoretical criterion. In this work, a self-designed soil permeability test device is used to conduct piping tests on a variety of soils that have different gradings and three different particle shapes. Based on the fractal theory and a capillary model, critical hydraulic conditions for soil piping are analyzed at multiple scales, and the testing process is monitored using an acoustic emission system. The results show that sand samples with spherical particle shape have relatively high permeability, prone to piping failure; with the increase of blocking particles, the soil tends to be stable under the action of seepage. The critical hydraulic gradient of soil piping is inversely proportional to the mass fractal dimension; the capillary model based on particle shape and effective pore volume predicts the critical flow rate of piping with a satisfactory accuracy. The evolution patterns of acoustic emission cumulative energy can reflect the characteristics of soil piping development.

Key words: hydraulic engineering；piping, particle shape, acoustic emission technique, capillary model