Estudo de parâmetros geomecânicos de uma célula experimental de resíduos sólidos urbanos com métodos geofísicos

Abstract

The sanitary landfills in Brazil have a high organic content (around 50%), a variety of mixed wastes, and low compaction energy. These characteristics are unusual in the well-studied landfills of developed countries. Improper landfill characterization may lead to groundwater contamination and slope instability. Therefore, it is crucial to understand the behaviour and physical properties of poorly characterized landfills to prevent environmental risks in Brazil. A geophysical survey was performed on the municipal solid waste (MSW) in an experimental cell and a lysimeter located in the city of Campinas, State of São Paulo. Geophysical methods such as seismic refraction, active and passive multichannel analysis of surface waves, crosshole test, electro resistivity and induced polarization were used to estimate physical and elastic parameters of the solid waste. The resulting estimates were unit weight, moisture content, shear modulus, Poisson's ratio, elastic modulus, and the elastic wave velocities. The compressive wave velocity (Vp) and the shear wave velocity (Vs) were used to characterize and derive the dynamic and elastic properties of the MSW, used to generate a stability analysis. The crosshole test showed that the Vp ranged from 217 to 252 m/s and the Vs ranged from 86 to 89 m/s. These low Vp and Vs values were attributed to the high content of organic material (53 %), low compaction energy, and climatic conditions such as high pluviometry index and high temperatures. All these variables directly affect the pore fluid saturation, effective stress, and pore pressure. The low velocities estimated at the MSW were consistent with values reported in the literature and landfills located in countries with analogous socioeconomic and climatic conditions. Two boreholes in the experimental cell were used to perform an electrical resistivity test and a moisture analysis. The direct correlation between the electrical resistivity results and the volumetric moisture content was estimated using Archie´s law. The calculated Archie's law parameters allowed the estimation of the tomography moisture content from the resistivity tomography. The joint analysis of moisture content, resistivity tomography, induced polarization and water balance in the experimental cell made possible to understand the humidity variation within the cell over time due to climatic conditions.