Research On The Characteristic Of Ground Vibrations And Infrasound Produced By Different Types Of Debris Flows

Debris flow is one of multiple geological disasters in China, it occurs suddenly with strongly destructive power. Development of early warning system for debris flow monitoring is an important early step to prevent mudslides. Recently, as a new technology for debris flows early warning, geosound and infrasound monitoring technology have attracted interest from domestic and abroad, and get certain application in practice as well, however, the alarm threshold setting of debris flow infrasound is still mainly depend on experience, because it lack of system theory and experimental research that can be used as guidance.This paper investigates the ground vibration and infrasound generated by different types of artificial simulation debris flow, aiming at providing the threshold value for a geosound-infrasound combined debris flows early warning system. The major works made in this dissertation were as follows:(1) A Geosound sensor, type GS-20DX made by Geospace Technologies and a A/D converter made by National Instruments Corporation were used to establish a geosound monitoring system based on the Labview platform; a debris flows infrasound monitoring equipment was also used to establish a debris flows infrasound monitoring system.(2) According to the fine granules content, debris flows was classified into three types, which are the boulder type, the cobble-gravelly type and the muddy type. We set three groups for each type of debris flows,9totally. Later we carried out an artificial debris flow simulation experiment at a steep slope, the signals of the ground vibration and infrasound, generated by debris flows in the process of particle collision and friction is measured by Geophone and infrasound sensors.(3) The monitoring signals in the time domain were transformed into the frequency domain by Fast Fourier Transfer and into the Time-Frequency domain by using the Gabor transform. The superiority of Gabor transform for analyzing the debris flow damping signal was also discussed.The experiment results show that, the geosound and infrasound generated by debris flows has its unique characteristics, so can be clearly distinguished from the environmental noise and water noise; When the fluid is concentrated, the main frequencies of geosound generated by boulder type and cobble-gravelly type debris flows is range from lOHz to300Hz, When the fluid is dispersed, signals in frequency range from300-500Hz has a significant increase, this becomes even more prominent with the increase of gravel content; the frequency range of the ground vibration associated with the muddy type debris flows is between10to300Hz. For the infrasound generated by debris flows, since infrasound itself is a very low frequency wave, the concentrated moving debris flows can increase its whole frequency range, for the boulder type debris flows and cobble-gravelly type debris flows here, their mainly frequency range is between3Hz to11Hz, when it comes to the muddy type, the mainly frequency range is between1Hz to4Hz; moreover, we found that, with the increase of large grave content, both the geosound and infrasound generated by debris flows are in a relatively low range, and with the small grave content increase, the frequency in relatively high range becomes more obvious; at last, a comparison analysis was present between the geosound signals and infrasound signals, we found that the geosound signal attenuates very quickly, it’s difficult to use it for the remote monitoring, while the infrasound monitoring technology can monitoring the remote infrasound signals much faster, consequently get more time for the debris flows early warning.