Mechanism of formation of Laojaoping debris flow, Chongqing, China

摘要

This paper makes a discussion on the mechatiism of formation of Laojaoping debris flow, Chongqing, China and on the cause and process of the debris flow transforming into a landslide, and a brief introduction to the emergent plan of engineering or works countermeasures for controlling the debris flow. Firstly, the discussion on the mechanism is involved in the following four aspects:. A. the basic conditions of formation of the debris flow, i.e. occurance of the favourable geomorphic unit, rich material source, steepy longitudinal slope and full rainfall; B. division of the four subareas of the debris flow area: a source subarea where a landslide occurs, an upper flow-path subarea where there are a lateral slide and a level ground which when passing through the debris flow moves slowly and stops temporarily, a lower flow-path subarea and an accumulation subarea, and determination of the genetic type of the debris flow, a typical landslidetyped debris flow; C. establishment of a flowing chart which shows the conditions, causes and process of formation of the debris flow and where the coiluviai-sliding accumulative materials in the IV area and the landslide in the III area evolve into the debris flow in the V area, and further explanation of the process of formation of the debris flow from the point of view of analysis of slope stability and based on Bigler's partical flow theory; and D. the dynamic and Kinetic characteristics of the debris flow. Next, the discussion on the cause and process indicates that having occurred, the debris flow transforms from flowing and rheological liquid mass into semiplastic-plastic quasisolid or solid mass existing in the depression, a low-lying land located in the accumulation subarea because of the reduction of the flow ve- cocity due to rainfall loss and drainage, and of water loss and evaporation during the dry season, and thus presents some of load and deformation characteristics similar to that of a landslide at ultimate equilibrium state, such as tension and shear fissures occurring in the flow-path subarea, and radiant fissures and tension fissures due to bulging emerging in the accumulation subarea, which makes clear that the debris flow has transformed into a landslide since then. Finally, the brief introduction to the emergent plan is made from the following two aspects: basic princi- ples followed by the design of the plan, and arrangements of 7 works or engineering countermeasure sys- tems for controlling the debris flow. Since completion of these control engineering or works they have worked both normally and well as a whole.