Rheological Characteristics Of Gengdi Debris Flow In Xichang,Sichuan Province

The research on the rheological characteristics of debris flow is an important branch of the application of rheology in the field of debris flow.The in-depth study on the rheological characteristics of debris flow is helpful to explore the internal mechanism among the movement mechanics characteristics,suspension mechanism and starting mechanism of debris flow,and to open up a new method for debris flow research.At 3:30 a.m.on August 8,2017,a debris flow disaster occurred in Gengdi village,Qiaowo Town,Puge County,Liangshan Yi Autonomous Prefecture,Sichuan Province.Groups 4 and 5 of Gengdi village,which is located at the exit of debris flow gully,were seriously affected.The disaster caused 577 people from 157 households to varying degrees,including 25 deaths and 5 injuries.In addition,71 houses were destroyed by the debris flow,resulting in a direct economic loss of 1 600 million yuan.In this paper,with the help of laser particle size analyzer and Anton Paar MCR 52 ball system rheometer and other instruments,through indoor screening,particle size analysis,organic matter content measurement,rock mineral content measurement,relative excess pore pressure measurement,slope rheological experiment and yield stress,shear stress and viscosity measurement experiments,the main factors affecting the rheological properties of Gengdi debris flow are explored,and the following conclusions are drawn:(1)In the study area,the gradient of gully bed is large,and the debris in the source area is more broken and loose due to the crossing of Zemuhe fault,and the soil stability is poor.In addition,the lack of effective precipitation in the source area before the occurrence of debris flow makes the soil in the source area more dry and loose.The short-term strong precipitation before the occurrence of debris flow quickly converges in a short period of time is the main inducement for the occurrence of debris flow,and the movement speed of debris flow is accelerated to a certain extent by several scarps formed by transverse cutting of several faults.(2)The debris flow deposits in Gengdi have a high correlation coefficient and obvious fractal structure.The debris flow has a strong hydrodynamic condition.Its movement mode is mainly traction rolling and jumping transportation,supplemented by suspension transportation.During the movement process,with the change of particle content of different particle sizes,the closer to the downstream accumulation fan,the higher the relative content of fine particles.On the whole,the debris flow deposits in Gengdi have the characteristics of wide gradation,good integrity,poor sorting and strong carrying capacity.(3)On the premise of keeping other conditions unchanged,the shear stress and shear rate of the debris flow slurry in Gengdi are in direct proportion to the change of shear rate,and the viscosity is in inverse proportion to the change of shear rate;at the initial stage of shear at high concentration,the shear stress and viscosity will change abruptly with the yield of the slurry,and then reach a dynamic equilibrium state with the damage and reconstruction of the flocculation structure of the debris flow slurry on the shear path,and the shear stress and viscosity will gradually stabilize with the change rate of shear rate.(4)At the same shear rate,the shear stress and viscosity of Gengdi debris flow slurry increase with the increase of volume concentration.When the volume concentration is greater than the critical value,the friction of coarse particles and the internal flocculation structure are further enhanced,and the shear stress and viscosity increased with the increase of volume concentration.(5)The smaller the upper limit particle size and the larger the specific surface area are,the stronger the flocculation structure is.Under the same volume concentration,the larger the shear stress and viscosity are.The variation of shear stress and viscosity of the slurry with large upper limit particle size with the volume concentration are less than that of the slurry with small upper limit particle size.(6)The flow curve and viscosity curve of Gengdi debris flow slurry and Jiangjiagou debris flow slurry are similar with the change trend of slurry volume concentration,but when the slurry volume concentration is greater than 0.496,compared with Gengdi debris flow,the flow curve and viscosity curve of Jiangjiagou debris flow slurry are relatively lower,and the liquidity of the slurry is greater,while when the slurry volume concentration is less than 0.496,it is opposite.I In addition,the rheological parameters of Gengdi debris flow and Jiangjiagou debris flow increase exponentially,and the influence of the volume concentration of the slurry on the rheological parameters of Gengdi debris flow is greater than that on the rheological parameters of Jiangjiagou debris flow.(7)Under the same conditions,the Gengdi debris flow and Jiangjiagou debris flow have similar ability of maintaining and dissipating relative excess pore pressure.However,the peak value of relative excess pore pressure of Gengdi debris flow slurry is larger than that of Jiangjiagou when the volume concentration of slurry is lower,which shows that the mobility and carrying capacity of Gengdi debris flow slurry is stronger than Jiangjiagou debris flow slurry when the volume concentration of slurry is lower.(8)The gradation,clay content,clay mineral composition and content as well as organic matter of the samples are the main factors affecting the slurry formation and mechanical characteristics of Jiangjiagou and Gengdi debris flows.The coincidence of the grading curves of the two experimental samples is very high,the composition of clay minerals is basically the same,and the clay content is also very close,but the content of clay minerals and organic matter is very different.These factors comprehensively affect the performance of rheological properties and the maintenance and dissipation of relative excess pore pressure in the two places.