Numerical Simulation Research On Bank Collapse Process With 2-D Flow Characteristics In The Danxikou Of Qujiang River

As an important issue in the interdisciplinary study of river dynamics and soil mechanics,river bank collapse is not only related to the characteristics of river bank flow and erosion and deposition,but also to factors such as the composition of the river bank and the mechanical properties of the river bank soil.As the process of bank collapse affects the development of the coastline,the control of the river regime,the safety of the embankment and the safety of life and property on the bank,it is necessary to comprehensively consider the effect of the near-shore water flow,the composition of the bank soil,the different water levels,and the erosion of the slope toe.Numerical simulation of the shore process,simulation of the change process of bank collapse,prediction of the time,scope and trend of bank collapse,providing technical support and reference for the construction and development of waterways.The main work of this paper is as follows:(1)Based on the soil mechanics model,a Bstem model capable of simulating bank collapse was established.The model is divided into a slope toe scour calculation module and a river bank stability calculation module.These two calculation modules are established through Excel VBA programming.The model first generates the bank profile by inputting the slope parameters and running the macro command,and then calculates the bank stability safety factor Fs by combining the characteristic parameters of the bank soil composition,the groundwater level and the pore water pressure,etc.(2)Based on the plane two-dimensional water flow mathematical model,the Bstem model that can simulate the bank collapse is embedded,and a mathematical model with two-dimensional water flow characteristics and bank collapse process is established.The model is required to reflect the influence of the characteristics of nearshore water flow in different periods on the river bank under the condition of fixed grid division,and it can simulate the bank avalanche process of a single or multi-branched channel.(3)Taking the Danxikou reach of Qujiang River as an example,a mathematical model with two-dimensional flow characteristics and bank collapse process was established.Comparing the changes in water level,water surface gradient,velocity and flow pattern along the shore of each typical section of the Danxikou reach in different periods,at the same time calculating the maximum scouring width and scouring amount of each typical section at different periods of the river bank,and then analyzing the flow slope toe The impact of erosion in the process of bank collapse.(4)Taking into account the slope toe erosion,water level changes along the way,the characteristics of the riparian soil,and the groundwater level,the stability analysis of the bank collapse process of each typical section in the Danxikou bank collapse area of Qujiang River is carried out,and the typical sections are calculated at the same time.Changes in the number of bank collapses,maximum collapse width,collapse amount and safety stability factor Fs in different periods.(5)Under the conditions of comprehensive consideration of the characteristics of the nearshore water flow,the erosion of the slope toe and the stability of the river bank,the bank collapse process of the bank line of the Danxikou bank collapse area and each typical section in the Qujiang River is simulated under the most unfavorable conditions.Finally,according to the Danxikou bank protection layout principle,combined with the two-dimensional water flow characteristics and the calculation results of the mathematical model of the bank collapse process and the actual survey situation,effective protection measures are proposed for the Danxikou bank collapse area.