Finite Release of Debris Flows around Round and Square Piers

Abstract

The impact pressure and force of debris flows on round and square piers were studied experimentally in a flume. Three distinctive flow regimes, namely, Types A, B, and C, were identified. Each debris flow regime has its unique behavior around the pier, which, in turn, influences the pressure and force on the structure. Two dimensionless numbers, namely, the grain Reynolds number and the modified Savage number, have to be used in combination for the classification of the three regimes. Both impact pressure and drag coefficients depend on debris flow regimes. For practical purposes, the pressure coefficient is .76 and 1.47 for Type A and Type B, respectively. The drag coefficient is 1.23 and .58 for Type A flow around square and round piers, respectively; in contrast, it is approximately .9 for Type B, regardless of the pier shape. The hydraulic model is unsuitable for nonfluid-like Type C flow, and the pressure and drag coefficients are not well defined. A new scaling law for impact pressure coefficient was also proposed.