C-3: Mechanics of Viscous Debris Flow and
Countermeasures for it
The viscous debris flow which brings tremendous disasters every year to the south-western part of China comprizes the dense clay and silt slurry and the highly concentrated coarse particles smaller than about a fist. It passes through a channel in fantastic speed as flat as 3°and this is the evident difference from the stony debris flow which is common in Japan and the north-eastern part of China. A peculiarity of the viscous debris flow is its intermittency; The bore like waves surge over again and again and between those waves the flow completely stops for a few tens of seconds or a few minutes. The photographs show the features of the wave and the fan deposit of those debris flows at the confluence to the major rivers.
The mechanics of occurrence, flowage and deposition, the rainfall condition for starting the debris flow, prediction of the magnitude of the flow and the methods to cope with the flow are the main themes for investigation, because understanding of those problems is indispensable for planning the countermeasures. Moreover, the comparative study of the viscous debris flow with the stony one is important in systematizing the debris flow investigation. From those points of view, we are implementing the joint research with Chendu Institute for Mountain Disaster and Environment, Chinese Academy of Sciences. The research plan contains the field observational and survey works at the Jiang-jia gully experimental basin of Dongchuan Debris Flow Observation Station of the Institute, the fundamental experiments in the laboratory and the development of the numerical simulation methods.
The research programs in this year are as follows:
1)As the automatic recorder systems of the rainfall and the debris flow had already been set in the basin last year, observations of the critical rainfall to start debris flow and the processes in occurrence and flowage will be continued this year.
2)The actual condition of topographical change before and after a debris flow will be surveyed at each occurrence, flowage and deposition area.
3)The soil on the slope, the debris flow consisting of material and the material in the deposits will be sampled and compared with those in Japanese stony debris flows.
4)The spot water sprinkle test on the slope will be executed. Water infiltration into the soil layer, change in the strength of the soil and the characteristics of the generated mini-debris flow will be measured.
5)The geographical informations of the Jiang-jia gully basin will be installed in the GIS equipment and prepare for the numerical simulation.
6)Investigation for the mechanism to sustain the coarse particles in the viscous debris flow will be continued in the laboratory experiments.
Fortunately, this joint research project will also be supported by the grant of aid for the scentific research by the Japanese Ministry of Education, Science and Culture for three years from this year. Five Japanese members will visit the spot to carry on field works in August and two Chinese members will be invited in October to discuss the results of these field works.
