Discussion of 'Laboratory Modeling of the Mechanisms of Piping Erosion Initiation' by Mandie S. Fleshman and John D. Rice

摘要

Evaluating piping in cohesionless soils remains an important and difficult problem when determining the safety of water-retaining structures. The more published piping research testing the better, especially when the researchers carefully describe some of the testing details as the authors have done and as Fleshman (2012) did more completely. They have presented a laboratory study of the effects on sand of saturated, vertical, upward water flow to a horizontal exit surface. They tested a variety of sands in a 51-mm diameter, 127-mm high cylindrical plexiglass sample holder and observed sand behavior while increasing the vertical seepage gradient. However, they also reported heaving, boiling, and quicksand behavior at vertical gradients higher, and, therefore, nonconserva-tive, versus Terzaghi's critical gradient i_(cr) [authors' Eq. (1)]. Eq. (1) expresses the static equilibrium of vertical forces during vertical-up seepage; namely the buoyant weight of sand = γ'Ⅴ versus the seepage force = i_(cr)γ_wⅤ wherein Ⅴ = volume.