Resumo:
The importance and impact that dams have on the economic, social, environmental, strategic,
and health levels make it necessary to maintain the safety and functionality of these projects.
Thus, one way to keep their physical and functional integrity is to perform temporal monitoring
through auscultation systems. Several instruments exist for this purpose, including piezometers,
pressure gauges, inclinometers, and flow gauges. Geophysical methods are already applied to
monitoring dams in several countries. With technological advances, they are becoming more
accurate and contributing to the interpretation of data obtained by conventional instrumentation.
Among the geophysical methods, the resistivity has great versatility in monitoring dams
because it has sensitivity in detecting saturation in the subsurface. Contribute to new
methodologies for monitoring dam this work realizes a case study. The chose of case study is
the Santa Helena earth dam, located in the city of Mirandópolis, São Paulo, which was
monitored monthly from August 2020 to January 2021 with the use of electroresistive
geophysics employing the electrical resistivity tomography technique with low-cost equipment
for data surveys. Two parallel lines 96 m wide were placed on the longitudinal axis on the dam
crest, the spacing between the electrodes was 2 m, which has allowed seven levels of
investigation, reaching approximately 7,5 m in depth. As a result, it was possible to see the
great influence of rainfall on the measured resistivity values, being very high in the dry months
and low in the wet season. In addition, with the aid of internal fluid flow models, it was possible
to verify that the system's water percolation behavior is the one expected in a homogeneous
dam. The unsaturated surface area increasing as it moves away from the reservoir detected in
inversions geophysics by increasing the resistivity in the subsurface from upstream to
downstream. Furthermore, the monitoring was able to detect an anomaly of low resistivity
positioned close to the surface, interpreted as a piping process caused by possible weakness
zones. The construction of a shelter to the adductor pump above the dam crest and the vibrations
related to its work might be the reason for the existence weakness zones. The present work
demonstrated that even using a limited measuring equipment, it was possible to monitor
resistivity variations that may indicate structural problems. It has confirmed that electroresistive geophysical techniques can greatly contribute to dam monitoring systems since their
dimensions range can be useful in interpreting the extent of anomalies punctually measured by
conventional instruments.