Abstract
A borehole radar investigation was performed at the Sanzuodian reservoir, Chifeng, China to assess possible leakage paths located in the deep dam foundation. The key methodologies used include both single-hole reflection and cross-hole radar tomography, which make a high-resolution identification of the hydraulic connection paths between upstream and downstream sides possible. The leakage paths are characterized by direct wave loss due to high electromagnetic attenuation in the single-hole reflection profile and the nearly horizontal-banded low-velocity zone in the cross-hole velocity tomography due to possible large internal erosion. Meanwhile, some small structures inside the dam, including the core wall thickness changing point, the connecting point between asphalt and concrete walls, and the contacting interface between the dry and the water-saturated formations can be identified from the single-hole reflection profile clearly. Interpreted leakage paths are proven by the water flow measurement. Borehole radar is a useful high-resolution tool, suitable for deep leakage detection and evaluation.
Highlights
Dam leakage is a very important issue for safety concerns in our society
Borehole radar is a geophysical tool which can overcome the shortcomings of surface ground penetrating radar (GPR), and which is characterized by deep investigation capability and high resolution [24]
We find that the direct wave disappears at certain intervals in all four profiles, as shown in Figure 4, i.e., from 660.3 m to 663.8 m for SYK8, from 659.5 m to 663.5 m for SYK4, from 657.6 m to 667.6 m for SYK7, from 655.4 m to 666.5 m for SYK5
Summary
Dam leakage is a very important issue for safety concerns in our society. The effective methods for dam leakage detection can be classified into non-geophysical and geophysical ones. Non-geophysical methods include isotope tracing and flow field detection, etc., while geophysical methods include ERT (Electrical Resistivity Tomography), self-potential (SP), electromagnetic (EM), electrical sounding (ES), and ground penetrating radar (GPR) et al [1,2,3,4,5,6,7,8,9,10]. Isotope tracing is an essential way to detect fluid flow. People use the tracing method to study a drainage gallery found in a hydropower station where the interconnection experiments have proved this result [1]. Flow field measurement is carried out within a borehole by a flow meter
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