Abstract
Reliable characterization of the karst system is essential for risk assessment where many associated hazards (e.g., cover-collapse dolines and groundwater pollution) can affect natural and built environments, threatening public safety. The use of multiple geophysical approaches may offer an improved way to investigate such cover-collapse sinkholes and aid in geohazard risk assessments. In this paper, covered karst, which has two types of shallow caves (vadose and fluvial) located in Tarimba (Goias, Brazil), was investigated using various geophysical methods to evaluate their efficiency in the delineation of the geometry of sediments filled sinkhole. The methods used for the investigation were Electrical Resistivity Tomography (ERT), Seismic Refraction Survey (SRS), Seismic Refraction Tomography (SRT) and the Very Low Frequency Electromagnetic (VLF-EM) method. The study developed several (2D) sections of the measured physical properties, including P-wave velocity and electrical resistivity, as well as the induced current (because of local bodies). For the analysis and processing of the data obtained from these methods, the following approaches were adopted: ERT inversion using a least-square scheme, Karous-Hjelt filter for VLF-EM data and time-distance curves and Vp cross-sections for the SRS. The refraction data analysis showed three-layered stratigraphy topsoil, claystone and carbonate bedrock, respectively. The findings obtained from ERT (three-layered stratigraphy and sediment-filled doline), as well as VLF-EM (fractured or filled caves as a positive anomaly), were found to be consistent with the actual field conditions. However, the SRS and SRT methods did not show the collapsed material and reached the limited the depth because of shorter profile lengths. The study provides a reasonable basis for the development of an integrated geophysical approach for site characterization of karst systems, particularly the perched tank and collapse doline.
Highlights
Karst landform is a geological feature that usually develops from the dissolution effect of groundwater on soluble carbonate rocks [1,2]
Geohazard assessments of karst areas must consider two crucial risks; firstly, the risk of subsidence caused by the collapse of the cavities; and secondly, the risk of pollution of the aquifers occupying the karst cavities, which can have an important role in the hydrodynamics therein, especially in arid and semiarid regions [9]
The present study reports a further geophysical investigation on the
Summary
Karst landform is a geological feature that usually develops from the dissolution effect of groundwater on soluble carbonate rocks [1,2]. Geohazard assessments of karst areas must consider two crucial risks; firstly, the risk of subsidence caused by the collapse of the cavities (geological hazard); and secondly, the risk of pollution of the aquifers occupying the karst cavities (environmental hazard), which can have an important role in the hydrodynamics therein, especially in arid and semiarid regions [9]. These underground cavities need to be well detected before commencing any construction activities or groundwater management projects, which is why the study of karst cavities is of great interest to civil engineers and hydrogeologists
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