An Improved Multilayer Compacted Clay Liner by Adding Bentonite and Phosphate Compound to Sandy Soil

Landfilling of municipal solid waste produces leachate containing heavy metals and different types of organic materials. On the other hand, it has been proven by researchers that dicalcium phosphate (DCP) is applicable for stabilizing of different heavy metals through the contaminated soil. This study aimed to investigate the effect of DCP on the permeability, cohesion and friction angle of a sand-bentonite liner. DCP was added by 0.2% of the dry weight of the base soil. Then, the permeability and shear strength were measured with water and synthetic leachate to assess the compatibility. Permeability coefficient of the sandy soil improved from about 10(-4) cm/s to less than 10(-7) cm/s. Results imply that DCP increases the compatibility of sand-bentonite mixture, and the leachate has less influence on this type of liner. By increasing the applied bentonite up to 6% in the base material liner, the internal friction angle reduces first and remains almost constant afterwards. For a certain vertical stress, adding 0.2% DCP to the sand-bentonite mixture increased the shear strain at the maximum shear strength and presents a positive effect. Therefore, a multilayer compacted clay liner is proposed that consists of a layer of DCP improved soil to increase the stabilization of heavy metals.