Hydromechanical Behavior of a Tuff/Bentonite Mixture Treated with Cement

Abstract

Sandy soil-clay mixtures are commonly used as a liner/barrier material in various engineering applications, such as construction of hydraulic and waste containment. In this study, the hydromechanical characteristics of tuff-bentonite and tuff-bentonite/cement mixtures are investigated to propose a local barrier material. A series of free swelling, one-dimensional consolidation and falling head permeability tests for hydraulic characteristics as well as the direct shear test for mechanical characteristics were performed on four different tuff-bentonite mixtures and two different tuff-bentonite/cement mixtures. Test results show that the compressibility/swelling behavior of the mixtures increases with increasing bentonite content. The optimum amount of bentonite to achieve a permeability of less than 10^–9 m/s, which is a liner/barrier design requirement, was found at 8% and 10%. The results of the strength tests indicate that the apparent cohesion increases with the bentonite content, while the apparent angle of friction decreases. Concerning the optimal mix treated with 3% and 5% cement, the test results show that the permeability and compressibility/swelling behavior decrease with the added cement content, while the angle of friction and cohesion increase. Finally, it was concluded that the 8% bentonite-92% tuff mixture treated with 3% cement is retained as a passive barrier material for landfill sites in arid and semi-arid regions.