Real-time measurement and preliminary analysis of debris-flow impact force at Jiangjia Ravine, China

Abstract

Impact forces associated with major debris flows (Jiangjia Ravine, China, August 25, 2004) were recorded in real time by a system consisting of three strain sensors installed at different flow depths. This provides the first real-time and long-duration record of impact forces associated with debris flows. A comprehensive approach including low-pass filtering and moving average methods were used to preprocess the recorded signals. The upper limit of impact frequency in the debris flows was estimated at 188.66 Hz under the assumption that only coarse grains cause effective impact loadings. Thus, a low-pass filter with a 200 Hz cut-off frequency was needed to denoise the original data in order to extract the impact force. Then the moving average method was applied to separate long-term and random components of the filtered data. These were interpreted as, respectively, the fluid pressure and grain impact loading. It was found that the peak grain impacts at different depths were non-synchronous within the debris flows. The impact loadings were far greater than, and not proportional to the fluid pressures. Analysis of the impact force of 38 debris flow surges gives an empirical value for the ratio of the hydrodynamic pressure to the momentum flow density, i.e. the product of debrisflow density and mean velocity square, which provides a very valuable basis for understanding debris flow dynamics and designing debris flow management systems. Copyright (C) 2011 John Wiley & Sons, Ltd.