Advanced Geological Prediction in Tunnels with Ground Penetrating Radar

Advanced geological prediction is the core technical system for the safe construction of tunnels. According to the detection principle, its methods can be divided into three categories: geological analysis method, drilling method, and geophysical exploration method. Among them, Ground Penetrating Radar, as a typical representative of geophysical exploration methods, analyzes the underground structure by transmitting ultra - high - frequency electromagnetic waves in the megahertz (MHz) range (usually with a frequency range of 20 - 2000MHz) and receiving reflected signals. Its technical characteristics are as follows: Antennas in the low - frequency band (such as 20 - 200MHz) are relatively large in size, with strong electromagnetic wave penetration. The maximum detection depth can reach 30 meters, but the spatial resolution is relatively low. Antennas in the high - frequency band (such as 500 - 2000MHz) use compact pulsed antennas, with a resolution up to the centimeter - level, but the effective detection depth is only 3 - 5 meters.

In tunnel advanced geological prediction, the selection of antenna frequency needs to balance the dual requirements of detection depth and resolution accuracy. Taking a 100MHz shielded antenna as an example, its detection depth can reach 20 meters and it has a decimeter - level resolution, which is particularly suitable for identifying potential hazards such as karst caves and fault fracture zones within 10 - 15 meters in front of the tunnel face. The shielded design can effectively suppress the electromagnetic interference from the metal support structure in the tunnel and ensure data quality. In actual projects, technicians often use three - dimensional tomographic imaging technology to invert radar signals and combine with borehole verification (such as arranging horizontal drilling holes every 30 meters) to form a comprehensive prediction system of "geophysical exploration first, drilling verification second".

The advancement of this technology lies in: The integrity of rock masses can be judged by the intensity of time - domain reflected signals (the waveform of intact rock masses is uniform, and the fracture zone shows chaotic reflection characteristics). Combined with AI algorithms, it can automatically identify the boundaries of abnormal bodies. Compared with the traditional seismic wave method (TSP), it has a more refined shallow - layer analysis ability. In major projects such as pumped - storage power stations, Ground Penetrating Radar has become a key equipment for preventing geological disasters such as water inrush and rock burst.