Characteristic Analysis And Experimental Study Of Yangjiatun Debris Flow In Northern Guangxi

Due to its unique climatic,geological conditions and hydrological conditions,the northern of Guangxi was the most serious area of debris flow disaster in the province.In this paper,the characteristics of the valley,source characteristics,formation area,circulation area and accumulation area of Yangjiatun debris flow source area were analyzed by field investigation of the natural geography,topography,geological structure and hydrology.And effective reference for the calculation of the characteristic parameters of the debris flow,the risk assessment and engineering control measures were provided.At the same time,the characteristics of soil in debris flow source area and built model trough and rainfall simulation system to simulate the start process of debris flow under the conditions of rainfall and upstream water as well as the activated mechanism of debris flow were studied.Concluded as follow:?1?The soil grain size in debris flow source area was analyzed.According to Geotechnical Investigation Specification?GB50021-2001?,the soil samples at S2,S3and S4 were gravelly soils,while the soil samples at S1,S5 and S6 was sand,in addition to the accumulation of S1 grain size poor,the rest of the soil grain size was good.?2?According to analysis of the whole rock and clay minerals in the Yangjiatun debris flow source area,the results showed that the composition of clay and quartz,albite and microcline are 10%,66%,3%and 20%.The percentage of illite,kaolinite,vermiculite and illite vermiculite in clay minerals was 19%,34%,9%and 38%.?3?Permeation test of channel head in debris flow source area was carried out by modified 70 type infiltration apparatus.The results showed that the permeability coefficient of soil samples decreased with the increase of dry density at the same grain size.At the same density,the permeability coefficient was not association with the inhomogeneity coefficient and the curvature coefficient,but the permeability coefficient negatively correlated with ????d60/d30?and decreases with the increase of the value.?4?The direct shear test of the debris-flow accumulated soil at S5 showed that the cohesion of soil was affected by the water content,and the cohesion decreases with the increase of water content.The compactness of the soil had a great influence on shear strength of the soil.?5?The experiment of debris flow initiation under simulated rainfall condition showed that the debris flow of the northern Guangxi could not be formed by the rainfall directly acting on the loose bulk,but it was mainly caused by erosion.?6?By simulating the impact of upstream water on debris flow activated,the results showed that slope had a relationship with the critical flow and velocity of debris flow activated:Q=e^{3.71044-0.04069?+0.000414411?2} and v₂=e^{-0.20 645-0.04068?+0.000414314?2}.The increase of flow rate would shorten the activated time and increase the scale.The increase of slope would shorten the activated time and increase the cumulative erosion of the sediment.But when the slope was too large,the cumulative amount of erosion decreased.The activated mechanism could be summarized as"water flow scouring channel formation-channel slumping-clogging-collapse-sediment formation into debris flow."?7?The Yangjiatun debris flow area was in the middle dangerous area,and the engineering prevention and control measures in the disaster area were mainly to protect the natural vegetation on the cross-strait channel,and the circulation area adopts the flexible intercepting network to intercept the provenance of the provenance area.Flow channel,diversion dike,interception of debris flow accumulation body.