Study On Seepage Characteristics Of Coarse-grained Soil Based On Lattice Boltzmann Method And Experimental Verification

In this paper,the pore structure of coarse-grained soil is modeled by PFC2D software.Based on tianhe-2 supercomputer platform,the permeability characteristics of coarse-grained soil are simulated by lattice Boltzmann method.Firstly,the macro and micro effects of porosity and particle size on the permeability of coarse-grained soil are studied based on the single particle size of coarse-grained soil.Then,on the basis of single particle size,the permeability characteristics of coarse-grained soil in single particle size range are studied,and the prediction model of permeability coefficient of coarse-grained soil based on Kozeny Carman equation is proposed.Then,the applicability of the prediction model in the case of mixed particle size is discussed by the method of error analysis.In order to verify the prediction model of permeability coefficient of coarse-grained soil proposed in this paper,indoor tests are carried out by self-designed constant head permeameter to verify the accuracy and applicability of the prediction model under the condition of single particle size range and different gradation.Finally,the prediction model obtained in this paper is compared with other common prediction models of permeability coefficient,and the differences between the traditional prediction formula and this formula are discussed.The main conclusions are as follows(1)Lattice Boltzmann method can effectively simulate the seepage phenomenon of coarse-grained soil and study the microscopic mechanism of coarse-grained soil seepage.There are two main reasons for the increase of permeability coefficient caused by the increase of porosity of coarse-grained soil;The second is the increase of average pore channel size.(2)When the porosity of coarse-grained soil is small,the number of pore channels is the main factor affecting the permeability characteristics;When the porosity is slightly larger,the average pore size is the dominant factor affecting the permeability.Under the comprehensive influence of porosity and particle size,the seepage channel of coarse-grained soil tends to develop to the steady state of seepage,that is,there are several channels with large average pore size and connecting along the main seepage direction.There is an obvious main channel phenomenon in coarse-grained soil seepage.That is to say,the seepage direction of coarse-grained soil preferentially selects the channel formed by the well connected pores,the flow velocity in the partially connected pores is relatively slow,and the flow velocity in the overall through channel is faster.(3)There is a large particle size effect in coarse-grained soil seepage,that is,the existence of large particle size will cause large pore width nearby,and will also cause wider seepage channels.These channels are generally the main seepage channels,and small particles will disturb the main seepage channels,or even change the direction of the main seepage channels.(4)Kozeny-Carman equation is more reasonable than other prediction models,but the parameter CK in the equation is not a fixed value,and its specific value is related to the development degree of pore channels.Through the study of micro mechanism of coarse-grained soil seepage characteristics,we can effectively reveal the reasons for the change of C_k value.Based on the simulation results of coarse-grained soil seepage,the value of C_k can be well modified,which makes the modified Kozeny-Carman equation more widely used and has very important theoretical and practical value.(5)By comparing with the test results of self-made constant head permeameter and the classical prediction model,it is proved that the accuracy and applicability of the prediction model proposed in this paper have been greatly improved in the calculation of permeability coefficient of coarse-grained soil.