Research Of Failure Mechanism And Disaster Prevention For Thick Alluvium And Diluvium Slope In Strong Seepage Field

In the past literatures, researches about the normal natural slope and artificial slope had been done deeply and broadly, but there were few of them studying about the complex and steep artificial slope, which was constituted with a top stratum of thick Quaternary alluvial and proluvial formation, and with the second stratum of intensely weathered rock, and with the slope foot of obvious down-dip joint surface base rock. In the practical engineering, some ore deposit are buried deeply under the Quaternary surface soil layer, if opencast working was used, a complex high and steep artificial slope would be formed. So the studying of buckling failure mechanism and disaster prevention and controlling measure of the slope has important theory value and practical significance. In this paper, on the basis of predecessors' research, supported by an important open pit slope project and the related research projects, a series of experimental research, field survey, drilling exploration, geophysical prospecting and numerical simulation had been carried on, then the mechanism of the slope instability failure and debris flow disaster-causing had been discussed systemically. Based on the trial and error, a feasible management plan was put forward to stop the slope water gushing. The main research and achievements of this thesis are as follows.(1) The stratum structure and mechanical parameters tests of the Quaternary and weathered base rock had been systemically carried out. Sampling in the supplementary investigation, aim at the Quaternary soil layer and the weathered base rock, a series of routine test and mechanical test had been carried out. Through investigation and experiment, the stratum structure, the flow velocity of under ground water, the rock and soil mechanical property of the slope had been acquired, and the test results indicated that under the condition of frequent soaking and drainage, the internal friction angle of the silty soil had a little change, but its cohesive strength had sharply decreased. It also indicated that the Quaternary surface soil was lightly affected by the earthquake at the level of 7,8 degree, so the disaster by vibrating liquefaction would not occur.(2) The potential debris flow hazards and slope stability in rainy season had been evaluated. Tests such as foundation trench seepage experiments, static shear strength test for the debris flow and analysis of the slope failure, revealed the soil mechanism of repeatedly wet and dye effect, hydraulic flushing effect, argillation by long-term immersion, vibration liquefaction, and the cause of debris flow of soil type. The slope stability under different rainfall intensity had been evaluated by numerical simulation, getting the law of the debris flow on Quaternary slope, and formulated a series measures to control and monitoring of the slope hazards.(3) Stability evaluation of the Quaternary stratum and weathered zone slope showed that the alluvium of the slope under the current condition was in the critical stable state, which might induced debris flow. The result of the evaluation gave safety factor for the current slope and the design slope. Through numerical simulation and analysis, it was concluded that under the premise of no protective measures, the slope angle of Quaternary slope was 32°(the original design angle was 35°). Then protection and monitoring program was given to keep the original design slope angle. Based on the geologic conditions, calculation method was established to simulate the movement of debris flow, and predict its scope.(4) The program of slope water plugging had optimized. According to the characteristics of the Quaternary strata structure and the underground flow field, the importance and complexity of the slope, a series of grouting tests and grouting material proportioning tests had been done to reveal the water plugging mechanism in pebble stratum under the condition of high seepage velocity. Through repeated comparison and process optimization, the scientific and reasonable water prevention and control program for the special thick alluvium had been put forward, and obtained the good economic and social benefits after implementation.