The determination of the location of a leak in full coverage tunnel waterproofing systems represents an important task during the investigation of existing double-shell tunnel linings. The exact determination of the location of a leak provides several advantages during the planning and realisation of repairs. These include the optimization of construction procedures by enabling selective repairs as well as improved estimations of costs and schedules. Destructive investigations to determine the location of a leak are usually not practical or economical. Reliable non-destructive methods are therefore in demand. Thermography has been applied for several years within the framework of condition assessments in tunnels. Successful application have been documented in locating the boundaries of problem areas of structures as well as in the localization of existing points of water inflow, damp areas and water behind the lining. Within the scope of the proposed research project, the question of whether portable thermographic cameras are suited for the precise determination of the leakage point in double-shell underground structures is to be investigated.
Within the scope of the proposed research project, the question of whether portable thermographic cameras are suited for the precise determination of the leakage point in double-shell underground structures will be investigated. The project will also answer / analyse the following issues:
- Understanding of possible damage mechanisms in tunnel waterproofing systems
- The design and materials of the investigated tunnel linings
- A visual inspection of the structure in the area of question
- An evaluation of thermographic images
- Knowledge of the principles and limits of thermography and thermographic devices
Through literature review and consultations with experts in geophysics or thermography the theoretical part of the research plan is processed. Field measurements are carried out in buildings which have different framework conditions. Findings obtained for the use of portable devices for thermographic state detection are presented.
Damage to a tunnel lining reduces the support resistance and the service life of the structure, thereby impairing long-term safety of the infrastructure buildings. Experiences from health scans of existing tunnels have shown that the water is involved or responsible for very many losses in various forms. A water inlet in a tunnel structure is often the origin of a chain of further damage patterns. If a defect in a sealing foil bivalve tunnel vault, it must be clarified first, where the leak is located behind the inner shell. Most of the water entry point is not identical to the leak. The evaluation of several km thermographic images have shown that the successful use of thermography behind the cladding is clearly possible in the definition of structural problem areas as well as in the localization of existing water intakes, damp places and water. The question of whether thermographic devices allow reliable detection of leaks in bivalve below ground structures has been not been specifically studied.
The research plan includes a theoretical part, by the necessary application-related aspects of thermography are determined for successful measurement and a practical part, by thermographic shots will be taken in the field to existing tunnels. The work program is in the phases "prepare", "Phase 1 fieldwork" "fieldwork phase 2" and "results / report" divided and requires 1.5 years.