Estimation of unsaturated permeability in a sanitary landfill cover layer in the Brazilian semiarid region

Abstract

The sanitary landfill cover layer has the main function of minimizing the flow of toxic gases into the atmosphere and reducing the infiltration of rainwater into the massif. However, permeability to water in saturated conditions (k_sat) does not convey the actual situation in which the soil is found, especially in landfills in semi-arid regions, and permeability in the unsaturated condition (k_nsat) is essential to understand the behavior of this layer. Thus, this work aimed to estimate the k_nsat behavior of a soil used in the cover layer of a sanitary landfill in the Brazilian semiarid region. The geotechnical characterization of the soil was carried out and, then, the behavior of the suction with variations in volumetric moisture was verified. Subsequently, the adjustment of the retention curves was carried out, obtaining the model that presents the best fit. From the data obtained for k_sat, it was possible to infer the values of k_nsat. The experimental data show that the model that presented the best fit obtained k_nsat values between 10-7 and 10-15 m/s. Thus, it was verified that the low humidity observed in the soils of this region promote a sudden decrease in the permeability to water in the unsaturated condition, favoring the use of this soil in layers of cover of sanitary landfills. With the knowledge of the behavior of this permeability, it is possible to have control of the execution process and the consequent reduction of risks of environmental accidents, either by the migration of gases to the atmosphere or by the increase in the level of liquids in the sanitary cell.

Keywords:
unsaturated permeability; filter paper method; retention curve