CARINA SCHMITZ FROM THE LGA INSTITUTE FOR ENVIRONMENTAL GEOLOGY AND CONTAMINATED SITES GMBH HAS SURVEYED NINE CELLARS IN THE CITY.
For the geographer Carina Schmitz, Franconian cellars are study objects that she visits professionally. The specialist in rock stabilization goes into cellars more often than "on the cellar"; her drive is the engineering geological investigation. Recently, her employer, the LGA Institute for Environmental Geology and Contaminated Sites GmbH – an independent GmbH with LGA participation since 2002 – received the order to investigate road traffic safety in the area of nine urban cellars.
The 30-year-old master's graduate from Bonn is a specialist in rock stabilization on above-ground slopes and masses – the underground work came about additionally: "My task is to manage the project for the client and our employees and to carry out the geological survey myself," she explains, making no secret of the fact that she landed her dream job with her first employer after graduation. In addition to the underground investigation, her tasks include documenting the work, evaluating the findings, as well as managing the budget and preparing cost estimates for the client.
Cellars – often accessed through private houses – are initially surveyed for the condition of the ceiling and walls. Cracks, recent breakouts, root penetrations, wet spots, and similar issues are examined and marked with numbers. To also check the thickness of the ceiling – which is crucial for the traffic safety of roads above the cellars – digital high-tech equipment is used: colleague Martin Harder captures the cellars with a 3-D laser scanner and measures both the underground tunnels and the surface terrain, including streets and house fronts above ground. This creates a cohesive model that shows the distance between the cellar ceiling and the surface terrain, as well as the street boundary in relation to the cellars.
A next step – if traffic safety could not yet be judged with certainty – is the so-called heavy dynamic probing: A drilling company drives a standardized cone tip into the ground from the street surface. The driving resistance indicates the depth of the rock surface and thus the "thickness of the cellar ceiling." "It makes a difference whether there is mainly loose material or rock, which bears much more weight," explains Schmitz.
THE 3-D LASER SCAN
Fascinating three-dimensional models show the positional relationship in and on the cellar. The images are created with a Leica BLK360 laser scanner; it captures the surroundings with full-color panoramic images overlaid on a highly accurate point cloud. "At high zoom levels, you can see that the supposed model consists of individual points," explains Carina Schmitz. In the cellar, up to seven meters of distance can be captured with a "click" – the scan takes three minutes, and the device is fixed on a tripod. "But this only applies to straight corridors; angled, obstacle-rich tunnels or stairs must be captured with multiple shots to ensure at least 50% overlap with the adjacent scan." Above ground, recordings are also made, and from both, fascinating overall models can be calculated, realistically depicting the cellar location, street, and buildings in any desired sections and projections.
