Study On Water Retention Characteristics Test Of Waste And Seepage Field Evolution Law Of Landfill

To build ecological civilization is a thousand-year plan for the sustainable development of the Chinese nation.Strengthening the disposal of waste and solving the problem of "garbage siege" is an important measure to enhance the construction of ecological civilization and accelerate green development.Landfill is an important way of harmless disposal of waste in our country.Ensuring the stability of landfills is a prerequisite for achieving ecological civilization and green development.The seepage field distribution of landfill is crucial to its structural stability and the design of drainage system.The water retention curve is the key to study unsaturated seepage flow.In this paper,a systematic study on the water retention characteristics of waste and the seepage field evolution law of landfill is carried out by means of indoor tests,theoretical analysis and numerical simulation.The main contents of the study are as follows:(1)Based on the previous research,the composition characteristics of 147 groups of wastes were collected in th is study.The change pattern of waste composition with landfill age was revealed,and the typical composition of waste in landfill was determined.Based on the vacuum pumping method,the experiment was carried out on specific gravity of the waste from a landfill in Xi’an,the typical composition of waste in landfills and each component of the waste.The effects of landfill age and composition on the specific gravity of waste were analyzed in depth.A mathematical model was established to calculate the specific gravity of waste based on the specific gravity and content of each component,and the accuracy of the model was verified by comparing the calculated results with the measured data.(2)The centrifuge method to measure the water retention curve of waste was carried out with a waste specimen aged 10 years from a landfill in Xi’an.The change of specimen volume during the test was analyzed.Based on the theoretical analysis,the calculation model of matrix suction and volumetric water content considering the volume change of specimens in the centrifugal test was established,and the method of centrifuge testing water retention curve was modified to improve the accuracy of the test results.The reliability of the corrected test results was verified by a conventional instrument pressure plate extractor.(3)Experimental study on the water retention curve of the typical composition waste in landfills and waste from a landfill in Xi’an was carried out.The mechanisms of landfill age,composition and compaction degree on the water retention curve were revealed.Based on the experimental results and statistical results,the correlation between the waste composition,porosity and water retention curve parameters were studied,the main influencing factors of water retention curve parameters θr,α and nv were determined.And the method of estimating water retention curve parameters based on the main influencing factors was proposed.(4)A saturated-unsaturated transient seepage model considering inner source water was developed,and a method to simulate inner source water by imposing a unit flow boundary of the source type on the regional surface was proposed.The effects of rainfall intensity,equivalent permeability coefficient of blind trench,compaction degree of waste,blind trench shape,blind trench spacing and diameter of the flower pipe on the seepage field were systematically investigated.Based on the orthogonal test method,impact of rainfall intensity,equivalent permeability coefficient of blind trench,compaction degree of waste,blind trench spacing and diameter of the flower pipe on the seepage field was evaluated.(5)Based on the saturated-unsaturated transient seepage model considering inner source water,the whole process of stratified landfill of a landfill in Xi’an is reproduced to reveal the dynamic change law of its seepage field.Based on the numerical calculation results,the changes of saturated zone area and leachate level with landfill operation time and landfill age were systematically studied and compared with the geological survey data,and the agreement was good,which verified the reasonableness of the endogenous water simulation method and the reliability of the seepage field simulation results.Based on the linear regression analysis method and numerical calculation results,a prediction model between the percentage of saturated area and the age of landfill was established.