Study On The Hydraulic Conductivity Of Sand-Bentonite Mixtures Used As Liner System Of Waste Landfill

The waste in the landfill will gradually generate leachate, which contains a lot of organic matters and heavy metals. If the leachate flows directly into the ground, it will contaminate the groundwater, affect the surrounding environment and the lives of the people living around. Therefore, a seepage system (liner system) must be set in a landfill. Common system consists of impermeable geomembrane, clay, etc. But clay of low permeability is difficult to obtain in some areas, especially in the hills and mountains, where large amount of sand with coarse particles exist. So using local materials to make impermeable material is of particularly importance.By testing the performance of bentonite、sand and other raw materials and the permeability evaluation of mixed soil, the following results can be obtained:(1) Due to the permeability coefficient of the bentonite mixed soil is small, which is generally less than10-5cm/s, it’s difficult to use ordinary rigid fixed water head or variable water head method for measuring. By a simple modification of ordinary triaxial apparatus, measuring of the permeability coefficient of mixed soil could be capable. With the content of bentonite in mixed soil increasing, the permeability coefficient significantly reduced, but after the content passes5%, the influence of bentonite content on permeability coefficient decreases, indicating that a preferred range of bentonite content exists.(2) Under identical conditions, there is a close relationship between the mixed soil permeability coefficient and the relative density. With the increase of relative density, mixed soil permeability coefficient dramatically decreased.(3) Under circumstances when the content of bentonite is constant, as the mixed soil moisture content increases, the permeability coefficient decreases, but when the moisture content exceeds a certain amount, the permeability coefficient increases again. Overall, the permeability coefficient of mixed soil reaches the minimum when the moisture content arrives around the optimum moisture content.(4) The calculation method of the optimum content of bentonite is proposed. Based on the consideration of the void ratio, the determination of the optimum content of bentonite is proposed, which may lessen the workload to some extent.