Geological assessment with High resolution Prosilica GT cameras
Tunnel boring machines (TBMs) are increasingly being utilized in major projects such as the Brenner Base Tunnel in the Austrian Alps. But the geological documentation of the drilling face lies behind that of conventional tunnel drives mainly due to visibility restrictions. In collaboration with Geodata GmbH, the Institute for Subsurface Engineering of Montanuniversität in Leoben, Austria has developed a camera system for boring machines used in tunnel construction projects, which helps solve this issue. High resolution Prosilica GT cameras mounted in the cutter head of a tunnel boring machine enable structural analysis and geological documentation of the drilling surface.
In conventional tunneling, geological mapping is usually performed by a geologist and is not impeded by an obstructed view to the face. However, in mechanized tunneling, the view to the face is obstructed by the cutter head. There are only a few openings through the cutter head, such as scrapers, cutting discs and manholes, which restrict the validity of the geological mapping of the face.
Camera-based rugged system
The Institute for Subsurface Engineering has developed a camera system, which, mounted in the disc housings, provides high resolution images and color-coded relief presentations of the entire face. Thus, mineral composition, spatial position of stratifications, and depth of cavities can be determined. This valuable information enables an assessment of the structural analysis and verification of the tendered geological model’s correctness, ensuring continuous tunnel boring free from disruption.
To expand coverage of the face area, the camera-based system was designed to be light and flexibly mounted in different disc housings. This enables TBMs without extra camera openings to be equipped with the camera system. The number of camera tracks can be adjusted to the distance between the retracted cutter head and the face. The camera system can be installed with a single camera or multiple cameras.
The control unit mounted in the disc housing of the double discs near the rotation center of the cutter head contains a PC, power supply, and a uniaxial inclination sensor. Additionally, the control unit provides interfaces to several cameras that can be operated in parallel to accelerate the measuring campaign if desired. The camera control software running on the PC is based on Allied Vision’s Software Development Kit, Vimba. The software triggers the camera in a fixed rate of 2 images per second, providing sufficient overlap and a surplus of images.
Perfect images for photogrammetry
The camera system provides high-resolution images for the photogrammetric analysis. Photogrammetry uses different measuring and evaluation methods to analyze digital images with the aim of creating a 3D model. The result is a dense 3D reconstruction of the entire face. A high resolution orthophoto (distortion-free, true-to-scale representation of the surface) showing equal illumination covering break-outs and stable face areas is created, providing details that cannot be seen behind the cutter head. Based on this image, a color-coded relief presentation of the face is also generated.
“Digital imaging of the face leads to objective geological mapping which offers an incontrovertible basis of geological assessment.” says Robert Wenighofer, Project Assistant at the Institute of Subsurface Engineering of Montanuniversität Leoben.
Power over Ethernet and Precise Iris
The rugged Prosilica GT2000 camera is designed to operate in extreme environments and fluctuating lighting conditions, paired with a 5 mm fixed focal length lens. The Prosilica GT2000 is set to continuous auto exposure within a region of interest that updates the exposure time for each image. This ensures equal illumination of the images covering both cavities and stable face. It also avoids overexposure/underexposure of the face so the images can be well processed by photogrammetric software.
The camera, equipped with the 2.2 Megapixel CMOSIS CMV2000 CMOS sensor, offers Precise iris (P-iris) lens control allowing users to fix the aperture size to optimize depth of field, exposure and gain without the need for additional control elements. Equipped with Power over Ethernet functionality (PoE), the camera can be operated with a single cable for power supply and data transfer, making the integration of the camera system into the cutter head very easy.
Highlights at a glance
The system enables an assessment of the structural analysis, ensuring continuous tunnel boring free from disruption.
The light and compact system can easily be mounted into different disc housings.
Automated geological mapping accelerates the drilling process and offers the workers with enhanced protection.
Camera designed to operate in extreme environments and fluctuating lighting conditions.