Study On The Bearing Capacity Deterioration Mechanism Of Village Building Foundation Under The Erosion Effect By Muddy Flood

Floods often occur suddenly.Under the effect of muddy flood soaking and scour,the bearing capacity of mountain village building foundation deteriorates which leads to the damage of village building foundation and superstructure.It has a serious impact on the safety of village building and is a chronic disease of village living environment governance.At present,many studies have made outstanding progress in the problems of superstructure damage and foundation bearing capacity deterioration under flood immersion of rural buildings.However,the mechanism of foundation bearing capacity deterioration under the effect of muddy flood remains to be further studied.The difficulty lies in the unclear description of velocity distribution in flood depth direction,inaccurate calculation of soil erosion depth and limited means of flood dynamic process analysis.As for the above problems,with the support of the National Key Research and Development Program(2018YFD1100401)and other projects,this thesis carried out research on the whole process of muddy flood "vertical distribution of velocity-calculation of erosion depth-deterioration of bearing capacity-discussion of influencing factors",in order to provide a reference for the flood control design of buildings in rural areas.The main work and research results are as follows:(1)The scour ability of muddy flood to building foundation is related to the distribution of flood velocity.In order to solve the problem of inaccurate description of vertical distribution of sand-bearing flood velocity,in this thesis,a numerical model of smooth particle hydrodynamics(SPH)based on Herschel-Bulkley-Papanastasiou(HBP)rheological constitutive model is developed to invert the three-dimensional flow process of debris flow in a large-scale flume experiment.A stratified statistical algorithm of velocity is proposed to obtain the velocity distribution of a large number of particles in the direction of flow depth.A nonlinear vertical distribution model of velocity based on logarithm function is established.The experimental data from several previous studies is used to verify the results.The results show that compared with the traditional linear model,the nonlinear distribution model proposed in this paper can fit the velocity profile more accurately and has stronger parameter robustness;(2)Given the limitations of the three-dimensional SPH numerical method on large regional scale and complex terrain simulation efficiency,the velocity vertical nonlinear distribution law obtained by threedimensional SPH numerical simulation is introduced into the erosion calculation model.A numerical model is developed to calculate the erosion process of foundation soil by flood,which is based on the depth simplified shallow water equation.In order to verify the reliability of the proposed method,the numerical inversion is carried out for a flume dam break test,and the erosion calculation results are compared with the experimental data.The results show that the error between the maximum erosion area and erosion depth obtained by numerical simulation and the experimental data is 4.10%,which demonstrates the accuracy of the proposed method;(3)Through field investigation,the characteristics of typical village building foundation are determined,and the three-dimensional model is generalized.The erosion calculation method based on the nonlinear distribution of velocity is adopted to calculate the scour depth of foundation.The three-dimensional foundation model before and after flood scouring is established.At the same time,the deterioration law of mechanical strength of foundation soil is combined with flood soaking.The bearing capacity of village building foundation and its variation law under the effect of flood scouring and soaking is analyzed using finite element method.The results show that without considering the flood soaking effect,the bearing capacity of foundation after erosion decreases by 26.10%,while the bearing capacity of foundation after erosion decreases by 47.88%under the coupling effect of soaking and scouring;(4)The sensitivity analysis of bearing capacity of rural building foundation under two key factors is carried out which include covering effect and flood scour angle.The variation of bearing capacity of village building foundation is studied under the determinant and staggered architectural layout and four different scour angles.The results show that under the same flood condition,the scour angle of flood has little effect on the bearing capacity of the foundation of village buildings,while the shielding effect of village buildings has a more significant effect on the bearing capacity of the foundation.The bearing capacity of foundation decreased by 47.88% under single building,29.69% under determinant layout,and 73.03% under staggered layout.