Multi-frequency GPR sounding

GPR profiles on the territory of the sand quarry

Application of the georadiolocation (GPR) method is very effective in condition of moraine and alluvial sediments and during studying of upper part of the loose sandy soil massif structure and the surface of bedrocks. At deep occurrence of groundwater level the use of dipole low-frequency antennas allows to reach the depth of 15-20 m, to trace the boundaries of the soil massif layers and the surface features of the bedrocks. The figure shows examples of georadar sections (75-150-900 MHz) that detail the structure of moraine soils above the surface of the bedrocks, and are an effective addition to the seismic method of reflected waves. The possibility of using in the complex of high frequency shielded antenna 900 MHz for these purposes is severely limited, since the penetration depth of the pulse is usually not more than 3-4 m, even in dry sandy soils.

GPR sounding of the ground foundation of  passenger quay embankment

The use of shielded high-frequency antenna is more effective within urban areas during detection of soil decompaction zones under hard surfaces of roads and pavements. An example of interpretation of bulk soil array sounding data is shown below. Under the cobblestone coating and crushed stone backfilling, there are areas of increased amplitudes of reflections and prolonged time of their registration associated with possible zones of decompaction and increased water saturation in sandy soil.

Examples of GPR profiles obtained using a shielded high frequency (900 MHz) antenna (left) and dipole low-frequency (150 MHz) antenna (right) at the berth area with cobblestone pavement.
The strongest reflecting boundaries are most likely associated with the surfaces of water-saturated lenses in a sandy massif. Due to accumulation of rainwater on the paving stones, it was possible their penetrate into the near-surface layer of crushed stone and soil, which significantly changes and complicates wave pattern on the records due to a sharp change in the dielectric permeability of the soil. Low-frequency radar sensing is a very effective method for mapping the surface of ground waters in sandy sediments. At the same time, the surface of water-saturated soils is a strong shielding boundary, below which the tracing of reflecting boundaries in the sandy-clay thickness is problematic.