Seepage Caused Damage To Sand Structure Intrinsic Mechanism And Mathematical Model

In the Three Gorges reservoir area,the soil bank slope consisting of residual and slope products is often seen.The grain group is mainly composed of 0.075mm-10 mm gravel and medium-fine breccia,containing broken stones.The periodic fluctuation of the reservoir water will cause coarse-grained soil.The loss of fine particles in the bank slope leads to deformation of the bank slope.Therefore,the erosive evolution model of coarse-grained soil under the action of up-and-down loading and unloading is established,and the intrinsic evoked mechanism of the seepage and erosion of coarse-grained soil under the cyclical fluctuation of reservoir water on the development of bank slope deformation is revealed and more accurately carried out.The bank slope deformation analysis and prediction provides theoretical basis and technical support,which has important guiding significance for the bank slope disaster prevention and mitigation treatment and the reservoir water level lifting speed regulation.In this paper,a self-made permeation erosion device is used to conduct seepage tests on soil samples with different hydraulic gradients and pore ratios,and the loss of fine particles in soil samples is obtained,and a functional relationship model between hydraulic gradient,void ratio and soil structure damage is established.Combining the parameter compression coefficient λ,the rebound coefficient κ and the axial failure value M and the damage coefficient D in the Cambridge model to establish the mathematical model of seepage damage of rock and soil is a key research and discussion in this paper.To this end,this article has done some work within the following aspects.1)When the osmotic pressure is applied,the downstream end of the sample is the first to suffer from seepage erosion.With the extension of the test time,the sample will be discharged with the water flow with repeated loading and unloading.When the unloading period is extended,cracks will gradually form around the sample.After each loading,the sample will be squeezed,and the crack will reappear after unloading.Finally,the crack will gradually expand to form a water flow channel,and the sample is relieved.During the process,the fine particles also flow out from the seepage channel with the water flow,thereby changing the original skeleton of the sample.2)As the hydraulic gradient increases,the flow velocity of the seepage increases linearly,and the fine particles inside the sample gradually change from a stationary state to a critical starting state.At the critical starting state,a small amount of fine particles can be observed to gush out the sample,but the gushing speed is extremely slow,and the sand blasting process is intermittent.The hydraulic gradient corresponding to the critical state of the sample is defined as the critical hydraulic gradient.The same critical hydraulic gradient value under the sameinitial porosity ratio can be defined as the starting hydraulic gradienti 0 of fine particle loss,and the value is obtained through trial and error.Theinitial porosity ratio is determined to be 0.45,0.65 and 0.85.The starting hydraulic gradients under conditions are 80,60 and 40,respectively.3)With the continuous development of seepage,the flowable fine particlgradually move away from the original position,and the particle composition at different positionsi nside the sample is different to form a dominant flow region.The seepage velocity at the dominant flow region is larger than the flow velocity at other locations of the sample,and the fine particles at the location are more likely to be carried away from the soil by the osmotic flow,and the particle distribution formed after the movement of the fine particles is adversely affected.Pore changes.Therefore,there is a mutualinfluence relationship between pore change and particle motion.Based on the observed phenomena,the pore change during the development of seepage can be divided into the following stages: the uni form distribution of pores;the initial formation of local dominant flow;the sample forms a distinct dominant flow;the particle loss reaches equilibrium.4)When the seepage erosion occurs in the sample,the pore flow of the soil changes from a uniform distribution to a large difference in the pore flow at the upper and lower positions of the sample.The dominant flow area has undergone a process of change from scratch,from small to large,from nothing to nothing.Under the same initial porosity ratio,the loss of accumulated lost fine particles will eventually tend to a stable value.Therefore,it can be inferred that during the loss process,the skeleton particles are also recombined and will gradually stabilize,which makes the current hydraulic gradient insufficient.In order to remove the fine particles,the amount of fine particles lost will stabilize.5)The influence of hydraulic gradient,void ratio and time on the loss of fine particles of soil samples was studied by seepage test.The hydraulic gradient,void ratio and time are the influencing factors,and the loss of fine particles is the dependent variable.The amount of fine particle loss is defined as the damage variable,and the data is collected by different influencing factors,and the relationship between the damage variable and the soil hydraulic gradient,void ratio and time is obtained.6)Based on the nonlinear incremental law proposed by Sterpi,the experimental model of seepage erosion in this test is preliminarily constructed.The data of the test data is processed by Excel to obtain the parameter value b=0.8 in the mathematical model;c=0.3;d=1.5.The experimental data was fitted using the test model.7)Combining the parameters λ,κ and M in the Cambridge model,the mechanical properties of sand under the erosion of seepage are explored.The mathematical model is to use the undisturbed soil as an initial non-destructive material before seepage erosion,and completely destroy the seepage after seepage.As the material after the damage,the soil can be regarded as a composite of the undisturbed soil and the damaged soil during the seepage erosion process,thus establishing the structural damage model of the soil during the seepage erosion process.