PIPING SUSCEPTIBILITY AND FILTER CRITERIA FOR SANDS.

A laboratory flume with a transparent plastic top and filled with sand was used to investigate piping and filter criteria by subjecting the saturated sand specimen to variable pressure heads. With small initial pipes formed in the sand, the critical heads (gradients) required to initiate piping in six different sand gradations were determined. It was determined that piping requires a discontinuity as an initiator to concentrate vertical gradients, which, coupled with horizontal gradients, create erosion. However, meandering of the pipe could lead to decreased velocities, resulting in downstream deposition and self-healing tendencies. Gradation effect studies showed uniform fine grained sands are more susceptible to piping than coarse grained well-graded sands.