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Die Überwachung von Bauteilen aus Stahl- oder Spannbeton mit Ultraschall hat in Labor- und Technikumsversuchen schon vielversprechende Ergebnisse gezeigt. Besonders gute Resultate wurden dabei mit eingebetteten Ultraschalltrans-ducern und bei Auswertung der Daten mit der hochsensiblen Codawelleninterferometrie erzielt. Erfasst werden können neben Temperatur- und Feuchteeffekten auch Belastungszustände und jegliche Art von Schädigung, die mit Mikro- oder Makrorissbildung einhergeht.
Seit 2019 untersucht die DFG-Forschergruppe 2825 „CoDA“ (Sprecher: Prof. Christoph Gehlen, TU München) ver-schiedenste Aspekte dieser innovativen Technologie mit dem Ziel, Einflussgrößen quantitativ zu erfassen, Umweltein-flüsse zu korrigieren und 3D-Auswerteverfahren zu verbessern. Final soll eine am Bauwerk einsatzfähige Methode ent-stehen, die klassische Monitoringverfahren ergänzt und erweitert sowie Input zu einem Update des statischen Systems liefert.
Aufgaben der BAM in der Forschergruppe ist neben Verbesserung und Adaptierung der Messsystem und Sensorik auch Langzeitversuche an einem Großobjekt und Testinstallationen an Realbauwerken. Hierzu liegen erste Ergebnisse vor, die zeigen, dass die Technologie auch außerhalb des Labors einsatzfähig ist.
Die Überwachung von Bauteilen aus Stahl- oder Spannbeton mit Ultraschall hat in Labor- und Technikumsversuchen schon vielversprechende Ergebnisse gezeigt. Besonders gute Resultate wurden dabei mit eingebetteten Ultraschalltrans-ducern und bei Auswertung der Daten mit der hochsensiblen Codawelleninterferometrie erzielt. Erfasst werden können neben Temperatur- und Feuchteeffekten auch Belastungszustände und jegliche Art von Schädigung, die mit Mikro- oder Makrorissbildung einhergeht.
Seit 2019 untersucht die DFG-Forschergruppe 2825 „CoDA“ (Sprecher: Prof. Christoph Gehlen, TU München) ver-schiedenste Aspekte dieser innovativen Technologie mit dem Ziel, Einflussgrößen quantitativ zu erfassen, Umweltein-flüsse zu korrigieren und 3D-Auswerteverfahren zu verbessern. Final soll eine am Bauwerk einsatzfähige Methode ent-stehen, die klassische Monitoringverfahren ergänzt und erweitert sowie Input zu einem Update des statischen Systems liefert.
Aufgaben der BAM in der Forschergruppe ist neben Verbesserung und Adaptierung der Messsystem und Sensorik auch Langzeitversuche an einem Großobjekt und Testinstallationen an Realbauwerken. Hierzu liegen erste Ergebnisse vor, die zeigen, dass die Technologie auch außerhalb des Labors einsatzfähig ist.
Modern geophysical methods might be either directly applied to foundations or integrated into existing testing schemes to assist in quality assurance and inspections. This paper gives an overview on available ideas and some more detailed examples from the author `s work including:
- Vibrator technologies to improve pile integrity testing.
- Ideas from vertical seismic profiling used in multichannel pile inspection
- Cross- and downhole seismics to check the diameter of jet grouting columns
- Improving the parallel seismic methods for precise length measurement of piles and foundation walls
- Seismic migration methods to improve ultrasonic imaging of foundation slabs
- Seismological tools to monitor subtle changes in concrete constructions
The author strongly believes that the cooperation between geophysics and civil engineering, which is obviously becoming stronger and stronger, will lead to a large number of innovative approaches for investigations tasks currently still unresolved. A lot of challenges and chances for science and technology are right here.
Numerous case histories show evidence that geophysical
methods are valuable tools for levee inspection and
monitoring. National and international standards and
recommendations recommend the use of geophysics for a
variety of tasks. However, in some cases reported have
been flaws missed or false indications given. Due to the
larger variety in type, size and construction of levees and
the even larger variety of potential tasks and targets the
success of geophysical surveys still pretty much depends on
the available budget and the experience and capabilities of
the clients and contractors involved.
It is strongly recommended that all relevant parties agree
on the detailed objectives of the survey, required accuracy
and reliability of the results and any follow up measures.
For the most common tasks more research and practical
work using techniques as POD (probability of detection),
which are well established in other fields of non-destructive testing, would be of benefit.
Modern geophysical methods might be either directly applied to foundations or integrated into existing testing schemes to assist in quality assurance and inspections. This paper gives an overview on available ideas and some more detailed examples from the author `s work including:
- Vibrator technologies to improve pile integrity testing.
- Ideas from vertical seismic profiling used in multichannel pile inspection
- Cross- and downhole seismics to check the diameter of jet grouting columns
- Improving the parallel seismic methods for precise length measurement of piles and foundation walls
Seismic migration methods to improve ultrasonic imaging of foundation slabs
Seismological tools to monitor subtle changes in concrete constructions
The author strongly believes that the cooperation between geophysics and civil engineering, which is obviously becoming stronger and stronger, will lead to a large number of innovative approaches for investigations tasks currently still unresolved. A lot of challenges and chances for science and technology are right here.
Numerous case histories show evidence that geophysical methods are valuable tools for levee inspection and monitoring. National and international standards and recommendations recommend the use of geophysics for a variety of tasks. However, in some cases reported have been flaws missed or false indications given. Due to the larger variety in type, size and construction of levees and the even larger variety of potential tasks and targets the success of geophysical surveys still pretty much depends on the available budget and the experience and capabilities of the clients and contractors involved. It is strongly recommended that all relevant parties agree on the detailed objectives of the survey, required accuracy and reliability of the results and any follow up measures. For the most common tasks more research and practical work using techniques as POD (probability of detection), which are well established in other fields of non-destructive testing, would be of benefit.
Innovative seismic and resistivity tools for determining the diameter of jet grouting columns
(2016)
Jet grouting is used for soil improvement, foundation support and groundwater low control all over the world. It is well accepted and subject of standardization in many countries. However, some issues with the method remain. As the grout columns are produced in the subsurface without visual control in an often inhomogeneous soil, the prediction of the column’s diameter is still a challenge. All methods applied so far have their limitations.
The approach presented in this study is twofold. At Colorado School of Mines a resistivity probe has been developed, which is pushed into the fresh grout directly after production. ERT sections are measured and inverted. Given some background information is available, the diameter of the columns can be evaluated.
At BAM the focus has been on post-production investigations using seismic borehole methods. After hardening of the concrete seismic waves are sent through the column downhole (sensors placed in a casing in the column’s axis, source on top) and crosshole (source and sensor in boreholes on opposite sides of the column). We have developed a scheme to evaluate the diameter of the column based on travel time measurements without calibration. As this method is eventually more time and cost intensive we assume its application mainly for test columns. These are casted and dug out for visual inspection to determine appropriate grouting parameters. Our method would replace the often very cost intensive visual inspection.
Both approaches have been tested at three test columns produced at BAM’s test site at Horstwalde, Germany and on an actual constructions site. Both methods have been in good agreement with the diameters predicted by the jet grouting contractors, which were confirmed in one case by mechanical measurements.
Concrete is known to be a very useful, flexible and durable construction material. However, due to excess load, fatigue, chemical processes, freeze-thaw or reinforcement corrosion concrete may suffer from degradation. If detected too late, repair is difficult and expensive.
The propagation of ultrasonic waves is influenced by changes in the properties and structure of the material, including, but not limited to, stress, temperature, moisture content and microcracking. Ultrasonic velocieties thus may serve as indicators for structural health. Traditional ultrasonic methods as transmission time of flight measurements are used since decades, but are not sensible enough to show subtle changes. Coda Wave Interferometry (CWI), originally developed in seismology to detect stress changes in the earth's crust uses the information in the late part of ultrasonic signals originating from multiple reflections and scattering. Since a few years it is used by several researchers for lab experiments on concrete.
Meanwhile specialized sensors to be embedded in concrete have been developed. We have conducted several lab and a few field experiments, which will be reported here. The capabilities and limitations of CWI are summarized.