泥石流冲击力的野外测量

冲击作用是泥石流最为剧烈的一种破坏方式。泥石流的冲击力因此也成为泥石流工程防治和危险性分区中的重要参数。然而,由于其破坏力巨大,可靠的野外泥石流的冲击力数据比较少。2004年通过在云南蒋家沟建立的泥石流冲击力野外测试装置和新研制的力传感器以及数据采集系统,首次测得不同流深位置、长历时、波形完整的泥石流冲击力信号。原始信号经过低通滤波处理后,得到真实的泥石流冲击力数据。对数据的初步分析发现,在同等流速的条件下,连续流的冲击力要比阵性流的大得多。单就阵性流而言,泥石流的冲击力最大值也不是随流速而单调增加的,而应该跟它所携带的固体物质的大小有很密切的关系。最后,对不同位置的冲击力过程线的分析说明泥石流中中等粒径的石块多集中在龙头和流体表面,而大粒径的石块应该是在泥石流体中半悬浮运动。

FIELD MEASUREMENT OF IMPACT FORCE OF DEBRIS FLOW

The impacting manner of debris flow is the most destructive way for artificial constructions in the alluvial fan.Because of difficulties under the field condition,it is hard to directly obtain reliable field data of impact force.Model experiment and investigation of structural damage are the most usual approaches to acquire this kind of data.On August 25,2004,the channel change of Jiangjia Gully(Dongchuan,Southern China) brought an opportunity to measure the impact force in virtue of new pile foundation work and three sensors with gauge 10 kN.It is the first time to achieve a long-duration hydrograph of impact force with perfect wave profile at different flow depths.The sampling frequency of data acquisition system is 2 kHz,which is enough to capture the impulse caused by large-sized grain in the debris flows.After the raw data are denoised by low-pass filter designed using the combination of Fourier and wavelet transforms,it is found that the continuous flows in the first stage show greater impact than the subsequent surge flows at the similar velocity.As far as the surge flows are concerned,the velocity is not the predominant element which determines extreme impact pressure.It is argued that the collisions of big boulders suspended in the debris flows are responsible for the extreme values.The maximum impact pressure is equal to 2 628.4 kPa.Preliminary analysis of three pressure hydrographs of the same surge at different flow depths indicates that most of moderate-sized grains in the debris flows concentrate on the front and the upper surface of the fluid.This is of special significance for debris-flow protecting engineering design.