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- Parallel seismic (4)
- Parallel seismics (4)
- Pile integrity testing (4)
- Piles (4)
- Spektrale Induzierte Polarisation (4)
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Organisationseinheit der BAM
The reuse of existing foundations is considered in various construction Projects to save time and costs while avoiding unnecessary interference with other underground objects. Because the design and as-built drawings might not be complete and questions may arise regarding the condition of the foundations, a detailed investigation is a prerequisite for the planning process in most cases. Nondestructive testing (NDT) techniques are a core part of this endeavor.
The processes and procedure for foundation reuse planning are not yet standardized, and the possibilities and limitations of NDT methods are not known to many planners and stakeholders. The German research Project REFUND (2014–2016) has developed charts for the planning and Investigation process that consider available standards and the current state of the art in NDT.
These charts are separately available for single and strip, slab, and pile foundations. Available NDT methods have been compiled and evaluated for specific tasks at these foundation types, including their respective limitations.
The procedures have been successfully tested in two real-world projects. The results from these projects enable planners to improve the reliability of the process while potentially saving significant resources. This paper discusses the procedures for pile foundations and demonstrates the use of various NDT methods in a project on the reuse of electrical tower foundations.
Concrete piles are used as a foundation when the load capacity of the soil is insufficient or when the sustainable soil is found at a higher depth. Among other impact factors, the load capacity depends on the pile’s integrity and length.
Therefore, verifying these parameters using adequate methods is recommended. The most common procedure is the low-strain integrity test using the hammer impact method. Developed and established in the 1970s, this method uses stress waves induced by a hammer impact at the pile head and its reflections at impedance changes (length, defects, geometry changes) to estimate the length and defect locations. Although this method is widely used due to its low cost and fast conduction in situ, one disadvantage is its inability to classify the exact type of defect, i.e., crack, change in diameter, or concrete quality. Furthermore, very long and slender piles are difficult to test and small defects cannot be detected. In addition, it is necessary for the test engineer to hold a high level of experience and expertise in this field. The European Union–funded PileInspect project (2013–2016) aimed to compensate for these disadvantages by using a low-cost shaker as the excitation source and sophisticated artificial intelligence algorithms for damage detection (higher-order spectra method). Because this technology lacks the capacity to localize damages and verify the pile length, an additional impulse response (IR) measurement technique was developed using vibrational excitation and regularized deconvolution to extract the depth information from the data in a similar manner as the hammer method.
Simulations and subsequent experiments conducted at a test facility on 90-cm-diameter bored piles 11 m in length and containing cracks at approximately 4 m below the pile head confirmed the capacity to determine the pile length.
Damage diagnosis and localization, however, are more difficult than for the hammer method. Although the damaged piles could be distinguished from the intact piles, in a blind test, this method might lead to misinterpretations caused by perturbations arising from the deconvolution process. The results also indicated that the low-cost shaker used for these measurements might be inappropriate for
the transferal of sufficient energy. Although the IR method cannot compensate for the disadvantages of the hammer method by itself, it may enable the possibility of using long and fully controllable and repeatable signals (chirp, synthetic impacts, even noise, etc.) for pile integrity testing in the future.
Complex resistivity (CR) behavior of building material - first results of field scale measurements
(2008)
NDT investigation methods
(2006)
During the re-use process of existing concrete memebers like foundations information about geometry and location of piles or strip foundation is necessary. Ultrasonic echo with a need of only one-sided access may provide this information and help the engineer to assess foundations. Cost effectiveness by the re-use of foundations gains an increasing economic role due to decreasing average economic lifetime of buildings on urban sites. Results of systematic ultrasonic echo investigations at a slab from 75 cm to 125 cm thickness with ten different reinforcement ratios are presented. The influence of the varying reinforcement ratio and thickness on the reliability of the results is shown. Available data-processing algorithms based on reconstruction calculation and imaging of results to reveal the geometry of a slab and the location of piles or strip foundations are introduced. Practical guidance for the application of ultrasonic echo and its limits are presented to ensure reliable results.
The structural safety, durability and performance of the infrastructure is of primary interest in every country. An efficient system for early and regular structural assessment as well as for quality assurance during and after the construction of new structures and of reconstruction processes is urgently required. At BAM, NDT methods to be applied in civil engineering are developed and their application improved. From the experience of on-site assessments, quality assurance systems and methodologies for regular inspections are elaborated. This work is mainly performed in the frame of externally funded research projects.
RUFUS - Re-Use of Foundations on Urban Sites - Ein EU-Projekt zur Wiedernutzung von Fundamenten
(2003)
Improperly built or managed tailing dams pose major risks to human lives and the environment. Research for risk reduction by new technologies including slurry handlings, stochastic modelling, development of a parameter framework as well as work on legislation and authorisation procedures will be done in the EC-funded project TAILSAFE. Focus of this paper is on geophysial techniques for structure investigation and monitoring.
Pile testing as a NDT-CE (non-destructive-testing in civil engineering) method provides information about the condition of foundations. It is also used as a tool for quality control. Real size test fields with sound piles, piles with flaws and piles connected with a foundation allow calibration of measurement devices and method comparison under "real" conditions. Such a site is planned on a BAM testing area south of Berlin. The joint use facilitates the establishment of the testing site as a national or European reference site.
Tailings are the fine residue of the milling process in the mining industry and appear in slurry form being mixed with water during this process. Large tailings ponds are required to contain them, usually confined by man-made dams. Such tailings facilities pose considerable risk both to the environment and human lives.
A major interdisciplinary research project ('TAILSAFE') supported by European Union has been initiated with the aim to increase attention towards and reduce the risk posed by tailings facilities. Methods of parameter evaluation and measurement are being developed within the project and applied for the detection, assessment and improvement of the safety state of tailings dams and ponds.
One of the workpackages has his focus on non-destructive geophysical investigation methods. Geoelectrical (SIP), seismic and radar methods will be used to get information on the tailings dam structure and water content.
Spectral Induced Polarization - a Tool for Non-Destructive Testing of Soils and Building Materials
(2003)
The Spectral Induced Polarization (SIP) is a newly developed non-destructive geophysical method. It is an extension of conventional electrical resistivity measurements. By measuring additional parameters a more detailed investigation of the subsurface is possible. Up to now SIP is mainly used in mineral exploration, but the number of application examples from near surface geophysics and civil engineering is increasing. Results are presented from the investigation of slag heaps and measurements on bricks.
Zusammenfassung
In der Geophysik wird seit einiger Zeit das Verfahren der "Spektralen Induzierten Polarisation (SIP)"eingesetzt, um nähere Informationen über die Art, die Struktur und den Zustand des Bodens zu erhalten. Die Methode beruht auf der Messung des komplexen spezifischen elektrischen Widerstands im Frequenzbereich zwischen 1 mHz und 10 kHz.
Die SIP kann neue Möglichkeiten beim Einsatz elektrischer Verfahren in der Bauwerksuntersuchung eröffnen. So lassen sich beispielsweise Materialunterschiede von Feuchteinhomogenitäten trennen, was mit konventioneller Widerstandsmessung nicht möglich ist. Ebenfalls denkbar ist eine Detektion kontaminierter Bereiche (z. B. bei starker Belastung durch organische Substanzen oder Salze) im Mauerwerk.
Vorgestellt werden das Verfahrensprinzip, die Messtechnik und erste Ergebnisse von Messungen an Mauerwerksziegeln.