Study On The Erosion And Slumping Mechanism Of Sandy Loess Bank Slope In The Yellow River Desert Basin Based On Catastrophe Theory

The "ten tributaries" desert drainage basin in the upper reaches of the Yellow River is an important source of siltation in the Ningmeng River section.The desert coarse sand bank slope watershed gravity collapsing due to the erosion of rainstorm flood,pouring into the Yellow River in the form of hyper-concentrated flood.The sediment disaster seriously affects the stability of the ecosystem and the health of the Yellow River.In this paper,the typical tributary "Sudalaer" desert small watershed was selected as the research area,and field observation,catastrophe theory and numerical simulation were used as the main research methods to explore the mechanical mechanism of gravity erosion and slump process and types of desert coarse sand bank slope.Then to find the criterion of instability.Based on catastrophe theory to analyze the slump principle of simulation results.Finally,compare the simulation results with the measured data.The main research results were as follows:(1)Through data access and field investigation,using knowledge of soil mechanics and hydraulics to analyze the main factors affecting gravity erosion.And establish a generalized mechanical model of gravity erosion on the bank slope of Sudalaer.It is found that the erosion and slumping of the sandy loess bank slope has typical abrupt characteristics.Calculated the shear stress and compressive stress of the sand particles.Analyze the landslide pattern of the bank slope under the action of rainfall infiltration and slope toe erosion.The results showed that the transition process from coarse sand to loess in the "ten tributaries" surface material composition in the upper reaches of the Yellow River,the slope slides linearly as a whole,and the slope toe is mostly vertical or broken line collapse.Calculated the river bank widening distance and a rough calculation formula for slip surface area is obtained.(2)Based on catastrophe theory,a simple and intuitive overhead gap model is established,and derive model assumptions.Select compressive stress and shear stress as control variables,and volume strain x as state variables.Then the instability criterion of collapsible loess microstructure model can be calculated,respectively through the fold catastrophe model and the cusp catastrophe model.Then a specific criterion expression is given.It can be proved that the pore of collapsible loess microstructure model would collapsed,when the stress to meet the bifurcation point set equation of the catastrophe model,resulted in overall instability.(3)Finite element analysis software Abaqus is used to establish a real finite element model of the slope.Based on rainfall data captured earlier in the study area to analyze the influence of factors such as rainfall infiltration and foot flow on slope stability,then combine simulation results and measured data to verify the correctness of the theoretical formula.The results show that it is feasible and accurate to describe the erosion and slumping process of sandy loess bank slope based on catastrophe theory.Along with the increase of slope and rainfall intensity and rainfall duration,the critical mutation points appear in various cloud diagrams.Sliding bodies on sandy loess bank slopes mainly appear on the surface,showing layered and flaky.The coarse sand bank slope is broken-line sliding,and the sliding type is vertical.The simulation results are qualitatively consistent with the measured results.The difference between the theoretical calculation result and the actual measurement result is within 10%.The research results provide a reference for the study of the mechanism of the contribution of sediment to the river in the desert basin,and the quantitative estimation of the amount of bank erosion and landslides.It has practical guiding significance for improving the soil and water management in the region,and at the same time enriching the theoretical system of soil erosion.