Inversion Of Hydraulic Characteristic Parameters And Simulation Of Preferential Seepage In Refuse Soil

Unsaturated hydraulic characteristics of waste soil are the key to predict and evaluate the distribution and migration status of leachate in landfills.The strong heterogeneity of the rubbish soil structure causes the obvious dominant flow phenomenon in the leachate migration process.In order to further analyze the change mechanism of the unsaturated hydraulic characteristics of garbage soil and the effect of dominant flow.Based on the theory of porous media seepage and soil mechanics,this paper explores the prediction of the unsaturated hydraulic characteristic parameter change and the dominant seepage process of the garbage soil through a series of indoor tests,field tests and numerical inversion methods.The main results are as follows:(1)The indoor saturated water content,saturated permeability coefficient test experiments and multi-step gravity free outflow tests were carried out.The measured basic parameters and the monitored outflow data were used to numerically invert the relevant hydraulic parameters in the single permeability and dual permeability models.The result shows that dry density and particle size are the key factors that affect the saturated moisture content and hydraulic conductivity of wastes,while degradation age has little effect on them.The saturated moisture content has a linear relationship with dry density,and hydraulic conductivity has an exponential relationship with dry density under limited experimental data.The numerical inversion of the hydraulic characteristic parameters through the overflow method has the advantages of simplicity and efficiency.The hydraulic characteristics of stale waste with a dry density of 200?400 kg m-3 are as follows:When using the VGM model for characterization,the a and n change ranges are 0.181?0.21 cm-1 and 1.45?1.618,respectively,and the residual moisture content ?r change range is 0.092-0.147.When using the DPeM model for characterization,the parameters of matrix domains ?rm and nm can be approximated to be 1.16 and 1.36 times those of? and n in the VGM model,respectively.The reciprocal of air intake value ?m and Ksm must be studied and verified further.(2)Based on laboratory test and numerical inversion results,the reciprocal of air intake value ?m and Ksm must be studied and verified further.Dry density,particle size,and degradation age all impact the hydraulic characteristics of waste;that is,the more significant the dry density is,the lower the reciprocal of air entry pressure ? and pore size distribution index n are,and the higher the residual moisture content ?r will be.The influence of particle size on the hydraulic characteristics is opposite to that of dry density.The larger the degradation age is,the smaller are the reciprocal of air entry pressure ?,pore size distribution index n,and residual moisture content ?r.(3)This paper carried out an on-site pumping water injection test and compared the effects of theoretical methods on the calculation results of permeability.It was inverted by monitoring the water level change data of the pumping test.Unsaturated hydraulic characteristics of garbage soil.The results show that the saturated permeability coefficients of the obsolete landfills with a buried depth of 8m tested in the field test are all in the order of 10-6?10-5m/s,and different test methods have little effect on the saturated permeability coefficient test results;according to the pumping test results It is inferred that the pumping influence radius is about 15m,and the single well production flow rate is 0.33m3/h;the average residual water content of the garbage soil is 0.27,which is larger than the indoor test results,and the air intake value of the garbage soil is 2kPa and the pore size distribution index is 1.20.(4)Based on the superior flow effect of waste soil,a study on the distribution law of leachate in the waste dump under typical refilling process conditions was carried out.The prediction results show that:the recharge rate,recharge frequency,recharge volume,initial water content and other factors all have an impact on increasing the depth of influence of the leachate,infiltration volume and water storage rate;the recharge outflow calculated by the dual permeability model The amount is significantly higher than the traditional single permeability model;when the lower boundary hydrophobic process is simulated by the dual permeability model,nearly 95%of the leachate flows out of the matrix domain,and only 5%of the leachate flows out of the fissure domain,but there is still a dominant permeation During the process,the above results provide a theoretical basis for the optimal design of the landfill recharge and water supplement system.The paper have 41 pictures,11 tables and 127 references.