Experimental Study Of The Evolution Characteristics Of The Intrinsic Permeability And Porosity Of The Bulk Solid Waste

The void space gas flow inside the landfill is influenced not only by the overlying load but also by the biodegradation of waste solid matrix. And one of the most important research problems is how to assess landfill gas transfer laws and the efficiency of gas extraction well, which are significant of methane collection and recycling engineering. To solve the problem a quantitative research method is proposed and it is needful to establish a numerical model of intrinsic permeability and porosity. In the paper a forecast of the synergetic process of intrinsic permeability and porosity of landfill piles in a quantitative way is achieved based on a multidisciplinary cross theory include the porous medium gas-solid coupling seepage theory, the soil mechanics and the biodegradation kinetics, which is guided by a laboratory test. Moreover, the numerical simulation analysis of LFG migration is developed on the condition of seepage-stress fields coupling model. The main research contents are as follows:(1) Through the experiment of the synergetic process of intrinsic permeability and porosity of landfill piles with different overlying loads, the relationship of intrinsic permeability and porosity under different water contents is analyzed and a quantitative characteristic model is proposed. The traditional K-C model is not suitable for fitting the change law of intrinsic permeability and porosity, nevertheless, the power function (?=AnB) and the linear function (lg(?)=a+b lg(n)) fit it well with the test dates. The range of intrinsic permeability changes from 10-15 m2 to 10-12 m2 and the values of porosity are improved from 0.378 to 0.685 as the size of the testing model increases from 50mm to 500mm.(2) The change law of intrinsic permeability and porosity is analyzed after the waste degradation with the time of 1 month,2 months and 3months, respectively. The results show that intrinsic permeability and porosity decrease obviously with the increase of degradation time. Water content has a significant contribution to waste biodegradation and with the increase of biodegradation time the porosity decreases to the lowest value of 0.1 when the water content is 45%. At the same time the rangeability of intrinsic permeability reaches to four orders of magnitude. Analysis of the fitting model of intrinsic permeability and porosity with fresh waste and decomposed waste shows that the power function is suitable for fresh waste while the traditional K-C model is suitable for decomposed waste.(3) A numerical simulation of the efficiency of landfill gas extraction well is built based on the seepage-stress fields coupling model of LFG transport. Analyzed the gas transport law and forecasted the efficiency of gas extraction well. The results show that the gas pressure considering the k-n model is higher than the condition of without the k-n model. The average gas pressure under the condition of the k-n model is 0.346kPa higher than the situation of without the k-n model after 10 years since the landfill closes. The average flow rate of the gas extraction well is 14.8% higher than considering the function of load. On the other hand, the horizontal flow rate of LFG is improved substantially after a high permeability layer is joined inside the landfill. Meanwhile, it can prevent the landfill gas to escape to atmosphere and increase the collection of gas extraction well.The above results can provide theoretical basis and parametric support to enrich and perfect the further research of LFG migration and evolution characteristics under the condition of gas-solid coupling model. Moreover, they are useful to assess LFG transport law and design LFG collection and control system.