| 5.12 Wenchuan Earthquake induced a large number of collapsed landslide bodies,which provided abundant loose solid materials for the outbreak of debris flow after the earthquake.Most of the blocking dams were full after the earthquake,and the prevention and treatment effect was not ideal.The fundamental reason is that the special debris flow after the earthquake The source starting mechanism is not well-understood.The debris flow and dynamic reserves required for engineering design still use the conventional calculation method before the earthquake,resulting in large errors in the settlement results.So far,more than ten years have passed since the Wenchuan earthquake.The role of debris flow and water flow in the rainy season after the earthquake has made the channel source have gradually become one of the main sources of debris flow after the earthquake.The "broad and gentle" channel is characterized by slow slope of the gully bed,large watershed area,and large average width,which is conducive to accumulation of accumulation bodies.Large-scale debris flows may occur in extreme weather after the earthquake.Therefore,studying the starting mechanism and dynamic reserves evaluation of the "broad and gentle" channel source after the earthquake has important theoretical scientific value and engineering guidance significance.In this paper,the "wide and gentle"main ditch in the downstream of Qipangou is taken as the research object.On the basis of field investigation and data collection,the theoretical analysis and indoor model tests are used as research methods to analyze and study the "wide and gentle" debris flow channel in the earthquake area.Source start-up mechanism and erosion law,and established an evaluation model of dynamic reserves.The main conclusions are as follows:(1)The particle content and structural composition of the accumulation body affect the process of instability and erosion.Fine-grained soil appears fine grooves from the leading edge,and gradually develops into troughs to the trailing edge,forming gullies;coarse-grained soil collapses from the leading edge and is unstable,showing the characteristics of traceable erosion;upper fine lower coarse soil starts from the layered place Erosion,and then gradually penetrate to the rear edge;the upper coarse and lower fine soil is eroded by the leading edge,and the rear coarse particles slide the shovel to scrape the leading edge fine soil.(2)At the instant of debris flow start,coarse particles are mainly started in three forms:sliding,jumping,and rolling.Affected by the composition and structural characteristics of the accumulation body,it can be one or several forms of mixing;fine particles are raining at 33.2mm/h The migration along the longitudinal section under strong conditions is as follows:the internal pores of fine-grained soil are small,and the fine particles are easy to block under the action of seepage,and it is not easy to migrate and collect;It is easy to migrate and gather from the trailing edge to the middle;the upper fine lower coarse soil is located in the middle runoff area,and there is obvious migration and accumulation;except for the fine particles in the middle leading edge,the fine particle migration in the other parts is not obvious.(3)When the coarse-grained soil is 49.1 mm/h in rain intensity and 44.4 mm/h and 49.1 mm/h in the upper coarse and lower fine soil,the erosion width increases at the leading edge and then decreases due to the instability of the accumulation body due to collapse The erosion width of the remaining test groups decreases from the leading edge to the trailing edge;the erosion depth is directly related to the rain intensity.The greater the rain intensity,the greater the erosion depth.When the rain intensity is 33.2mm/h,the erosion depth curve is relatively gentle;when the rain intensity is 38.lmm/h?49.1mm/h,the undercut erosion is strong,and the curve has a tendency to increase first and then decrease,and the maximum erosion depth generally appears in front.The last or middle edge.(4)By using Origin Pro software to analyze and fit the test data,a dynamic reserve evaluation model with rainfall intensity as the influencing factor is obtained.Fine-grained soil:n=0.0011e^(q/4.875)+3.093;coarse-grained Soil:n=0.00005e^(q/3.74)+1.175;upper fine lower coarse soil:n=0.02062q^2-0.8803q+7.58828;upper coarse lower fine soil:n=1.86q-63.476(n(%)Is the percentage of dynamic reserves and total reserves;q is rainfall intensity).The typical wide and gentle ditch hoe and ditch ditch in the earthquake area were selected for verification.The calculation results are conservative and can meet the requirements.With the evolution of the channel source after the earthquake,the accuracy of the calculation results will gradually increase. |
PDF Full Text Request