Estudo da permeabilidade em solos utilizados em camada de base de aterro sanitário no semiárido paraibano.

Abstract

The liners of landfills are constituents which function is to prevent the flow of contaminants to subsoil and groundwater. One way of building liners is by using compacted soil as it is a viable and low-cost alternative when deposits are available on-site or in surrounding areas. The composition of soils with other materials, such as bentonite, for use in landfill liners becomes feasible when natural soil is unable to meet national and international standards and legislation due to its waterproofing properties. The aim of this work is to analyze the permeability in soil mixtures used in landfill base layers. The experimental field for the development of this work was the landfill in Campina Grande – PB, which performs the waterproofing base layer using two types of soils: local granular soil and bentonite. The great water retention capacity of bentonite and its high expansion capacity are characteristics that give the material resistance to water flow, which are characteristics of montmorillonite clay. In this study, several factors that influence the behavior of soil permeability were considered, among them, the bentonite content, compaction energy, compaction moisture, saturation degree and percolating fluid. With statistics, interactions with the various parameters were performed, such as bentonite content, compaction energy and compaction moisture of the mixture through a factorial design and using a central composite design. The experiments to determining the soil permeability were performed using the Tri-flex 2 permeameter with water and leachate as percolating fluid. The suction tests were performed in the Richards chamber, with normal Proctor compaction energy, using five soil types. With the studies performed it was observed that the soil of the waterproofing barrier base in its field condition, that is, in the unsaturated condition, meets the permeability coefficient values recommended by NBR 13896 (1997) and EPA (1993) to compose waterproofing barriers of landfill bases. The permeability tests results show that the bentonite content is the variable that displays the greatest influence on soil permeability. The soil with the bentonite addition functioned as an efficient filter to retain the solids dissolved in the leachate. The leachate use as a percolating fluid led to a reduction in soil permeability when compared to water, which allowed a reduction in the addition of bentonite for the liner design.