Laboratory measurement and prediction to the permeability of bentonite-modified loess as a landfill liner

Mixing of bentonite to a native soil is a convenient and economic means to make an impermeable earthen liner for landfills in a region where natural clay is deficient. In this investigation, laboratory permeability tests were conducted on the compacted specimens of loess and bentonite mixtures to study the feasibility of bentonite-modified loess as a landfill liner material. Two kinds of loess soils with different grain size compositions, the Lanzhou loess soil (LH) and Yulin loess soil (YH), were mixed with various contents of bentonite, and compacted to the maximum density for the measurement of permeability by a flexible-wall permeameter. The variation relationship between permeability coefficient and bentonite addition levels was analyzed; and the minimum addition of bentonite to loess soils was determined with respect to the regulations to MSW landfill liner. Scanning electronic microscopy (SEM) was conducted to observe the microstructure of the compacted loess soils with different contents of bentonite addition. It was found that the larger pores existed originally in loess soils were transformed into a larger number of small pores by bentonite addition, which is mainly responsible for the reduction of soil permeability. Based on the test data, a regression penetrative model governing the permeability and the bentonite addition was established for practical prediction.