The Tallinn City Government has decided to erect a sculpture in front of the Estonia Theater on Estonia Boulevard in honor of the 100th anniversary of the birth of Georg Ots, a well-known Estonian singer and actor. The erection of the sculpture requires the construction of a foundation, and it is necessary to determine whether there are any objects in the ground that could prevent this. Various geodetic base plans were available for the site, but their accuracy and reliability could not be guaranteed.
TASK
The existing geodetic base plans showed that there were many different underground utility networks in the survey area, but the data compared on the geodetic bases was contradictory.
The task of the georadar survey was to identify and map the exact locations and depths of all underground utility networks.
SOLUTION
Since the task was to accurately identify and map all underground utility networks, it was decided to use a high-resolution 3D GPR Raptor cart version. A 450 MHz antenna array was used, with a distance of 8 cm between the antennas, which scans 8 profiles in one pass. The entire survey area was scanned in one direction so that there were no gaps between the scan lines. A Trimble RTK GNSS device R8 and a TSC3 field computer were used for positioning. During the scanning of the area, the positioning device continuously sent NMEA data to the ground penetrating radar, which was linked to the GPR data.
RESULTS
A total of 15 survey lines were scanned in the survey area, resulting in 120 profiles with 8 cm spacing.
The data was post-processed using Macleod Simmonds’ special software GPRCAD. The aim of the data processing was to create visually distinguishable objects from the raw GPR data and then draw and export them in three-dimensional CAD format. The data obtained was compared with existing data on the city of Tallinn, and it became apparent that one large electrical cable shaft was missing from the city’s data. Thanks to the ground-penetrating radar survey, the data was supplemented and the location of the Georg Ots sculpture can now be determined on the basis of reliable data.
Results of the ground-penetrating radar survey of the Estonia Theater Square