Geophysical Methods To Identify Underground Erosion In Lateritic Soil

Underground erosion is a serious problem to development of urban areas in<br>the neighborhoods of Brasilia-Brazil. This problem was first identified in 1986, when the<br>occurrence of numerous pseudo-sinkholes condemned an area of 300,000 square meters,<br>causing the demolition of 52 houses. Occurrence of pseudo-sinkholes in other places<br>around Brasilia led the University of Brasilia Institute of Geology to investigate the<br>problem. The research focused on the determination of the factors that generate the<br>underground erosion, and analyzed the geological, hydrogeological, and geotechnical<br>characteristics of the areas where the pseudo-sinkholes were identified.<br>One of the most serious aspects of underground erosion is that it is only<br>detected at the surface, in advanced stages of evolution. When the pseudo-sinkholes start<br>to develop, the geotechnical conditions of the area are already jeopardized, implying huge<br>remediation costs. Therefore, the location of underground cavities in early stages of the<br>underground erosion process was considered a key issue, and the selection of geophysical<br>methodologies to locate the cavities were one of the focus of the research.<br>Eletroresistivity, microgravimetry, and the vertical gravimetric gradient were the<br>geophysical methodologies tested in the areas with underground erosion. The use of<br>geophysical methodologies proved to be of great value. The interpretation of geophysical<br>data, supported by geotechnical, geological, and hydrogeological studies, allowed the<br>identification of areas with potential risk for underground erosion. Geophysics<br>employment also permitted the precise location of the underground cavities.