Abstract
The town of Teresina, in the state of Piauí, Brazil, presents a history of land sinking processes. Two sinking events deserve to be highlighted, the first occurred in 1999 at Simplício Mendes Street and the other occurred on July 31, 2008, at Francisco Mendes Street. To identify possible shallow caves and associated structures, the Geological Survey of Brazil/CPRM developed a Ground Penetrating Radar (GPR) study to verify the occurrence of reflection patterns characteristic of these dissolution structures. In the field, the team conducted GPR sections along streets with a history of collapse. The GPR results obtained with shielded antennas of 200 MHz allowed the identification of old areas of collapse of the terrain, to a maximum depth of 3 m. In addition, the results obtained by this study show the potential of applying the GPR method in the characterization of the subsoil of paved streets, making it possible to identify various layers: asphalt, actual pavement, subgrade pavement, soil, saprolite, and mixed material. The high clay content of the subsoil does not allow the GPR to investigate further depths in the research area. The interpretation of aero-magnetometric data shows that the occurrence of sinkholes is associated with magnetic lineaments mainly in the NW–SE direction and enhances the understanding of the structural framework of the study area.
Highlights
In Brazil, the verticalization of urban spaces due to higher living standards and the construction of tall buildings in urban areas, in addition to the progressive growth of land use by mining, civil engineering, and agriculture activities, have generated impacts on the physical environment, as in the case of karst terrains
According to Vestena (2002), the subsidence which has occurred in the cities of Cajamar-SP, Sete Lagoas-MG, Almirante Tamandaré-PR, and Colombo-PR are associated with karst terrains, where the lowering of the water table contributed to the process of soil collapse / subsidence
Ground Penetrating Radar (GPR) investigations carried out on the streets and avenues of Teresina / PI show pedological coverage and / or landfill up to a maximum depth of 3 meters and hyperbolic targets related to underground interference
Summary
In Brazil, the verticalization of urban spaces due to higher living standards and the construction of tall buildings in urban areas, in addition to the progressive growth of land use by mining, civil engineering, and agriculture activities, have generated impacts on the physical environment, as in the case of karst terrains. In this context, the significant areas of karst terrains in several Brazilian cities (Cajamar-SP, Lapão-BA, Teresina-PI, Curvelo-MG, Bocaiúva do Sul-PR, Sete Lagoas-MG, Almirante Tamandaré-PR e Colombo-PR), means that there are potential geological risks for phenomena that generate subsidence and collapse of cavities under these cities. Subsidence sinkholes are the main risk in karst terrains (Waltham et al 2005; Gutiérrez 2010; Rodrigues et al 2014)
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