Due to climate change, weather conditions have become increasingly extreme and unpredictable today. In recent years, the population of Europe has experienced numerous heavy rains that caused localized flash floods or multi-day flood waves across national borders. Due to past, sometimes tragic events, increasing attention is being paid to prevention and the development of flood-prone areas. The inspection of flood protection dams reduces the risk of potential embankment breaches.
Both Electrical Resistivity Tomography (ERT) and GPR ground-penetrating radar are effective geophysical methods for monitoring the condition of dams, especially in the case of flood protection dams. The two methods identify problems found beneath the surface that can lead to dam failure in different ways. Here are their most important applications:
Application of Electrical Resistivity Tomography (ERT) in dam monitoring
The ERT method is effective for surveying the internal structure of dam bodies, and its most important applications are as follows:
1. Detection of leakage zones
- Specific electrical resistivity anomalies: Water infiltration and seepage within the dam body or its foundation cause changes in specific electrical resistivity. ERT can detect these anomalies by highlighting lower resistivity areas, which typically indicate larger saturated zones.
- Identification of leakage paths: ERT is suitable for mapping leakage paths and zones within the dam body. Continuous monitoring can provide early warning of dam failure.
2. Surveying the internal structure of the dam
- Heterogeneity detection: ERT provides a detailed image of the dam's internal structure, including areas containing different materials (e.g., clay, sand, or rock layers). This information is useful for assessing the uniformity of the dam's construction and for identifying weak or problematic zones.
- Compaction problems: Poorly compacted areas can cause instability. The ERT method is suitable for identifying these areas by detecting zones of higher porosity or water saturation.
Application of Ground Penetrating Radar (GPR) in dam monitoring
GPR ground radar maps subsurface layers using electromagnetic waves. Its application is ideal for high-resolution investigation of near-surface layers, offering greater resolution than the ERT method. Its main applications are as follows:
1. Identification of near-surface leakage zones
- High-resolution imaging: GPR surveys provide a high-resolution image of the dam's near-surface layers, making it excellent for detecting surface leakage zones that are not visible to the naked eye.
- Assessment of drainage system condition: GPR can locate and inspect the dam's internal drainage and filter systems. It can be used to check that they are functioning correctly and are not blocked.
2. Detection of cracks and cavities
GPR can identify smaller cracks or cavities within the dam's structure, which can be the starting points for larger problems that appear later, such as leaks or structural failures..
3. Mapping soil and material compaction
- Compaction monitoring: GPR can be used to assess the compaction quality of the dam's embankments, for example, identifying poorly compacted layers or voids caused by poor construction or erosion. Monitoring structural changes: GPR can track changes in subsurface layers over time, helping engineers detect potential displacements in the dam's structure that could jeopardize stability.
4. Monitoring reinforcements
- Identification of reinforcing materials: GPR is effective in identifying reinforcing materials used in the dam, such as geotextiles, concrete blocks, or metal anchors, and in checking their condition.