CC News - more details about our actual projects and work

In the actual edition of Bautechnik 10/2024 (https://doi.org/10.1002/bate.202300114), further results on the failure mechanism (load-bearing capacity tests) of grouted bodies for strand anchors are currently being published. This is a follow up publication after 2017. The focus of the work over the last two years has been on the development of a constitutive model based on the distributed strain sensing used for the investigation in order to determine the anchor bearing capacity (failure mechanisms) of single and staggered anchors with sufficient accuracy.
This work was carried out as part of the author's activities in the German Standards Committee “Grouted Anchors”. On the basis of this work, further investigations are currently being carried out to map the failure mechanism.
In this context, we would like to thank Porr Spezialtiefbau GmbH for their great support.

In the upcoming edition of Bautechnik 09/2024, the popular topic of determining the diameter of bored piles will be addressed under the title “Contribution to determining the diameter of piles based on Thermal Integrity Profiling”. New results will be presented on the basis of distributed temperature sensing and in the context of renewed simulations using COMSOL Multiphysics. Diameter determination tests were carried out on bored piles with and without special shapes. It is shown that the influencing factors in thermal integrity profiling are so diverse that it is not possible to draw conclusions about the diameter even if these influencing factors are predominantly taken into account.
The reasons for this are explained in detail by the authors in this article.

Today is finally the starting day! Over the next 48 hours, we will attempt to carry out one of the largest pile test loads in the world with a planned 120 MN (12,000 tons). This is a pile group test with five large bored piles with pile base expansion.
Where is the whole spectacel taking place, you ask? We are measuring in Hamburg (GER) against the backdrop of the #Kattwykbrücke.
But the most important thing for us, apart from the premiere of such a measuring arrangement, is the safety aspect at 120 MN. This was coordinated in advance with #PORR's corporate occupational safety department and BGBau. Thanks to Michael and Volker!
The hydraulic control system for this measuring arrangement was built by #A&K. Thanks to Sven!

We are now taking the next step in the application of distributed sensing. In collaboration with APSensing, we will be testing the first installations for vibration monitoring in urban metro structures in the coming months.
The relatively susceptible cable-guided electrodynamic vibration velocity transducers are always a challenge. They are relatively sensitive to electrical interference signals, which are also caused by railroad signaling systems. The transducers and their connecting cables are therefore subject to high requirements in terms of electrical shielding. These disadvantageous effects are completely eliminated by using Distributed Acoustic Sensing technology. It is even possible to detect vibrations from 0.01 Hz. Here we can draw on our partner's wealth of experience in seismic applications.
According to the current state of the art, lightweight and cost-effective geophones are used for vibration measurements. Due to the low vibrating mass in these small vibration velocity transducers, the natural frequencies of commercially available devices are around 4 Hz. Vibrations below the natural frequency are therefore only registered at a greatly reduced level and the transmission of vibration into an electrical signal is no longer linear, so that the transfer function must be equalized up to 1 Hz. This measure, whether electrical in the analog signal or computational in the digital signal, always contains uncertainties.
According to the current state of the art, lightweight and inexpensive geophones are used for vibration measurements. Due to the low vibrating mass in these small vibration velocity transducers, the natural frequencies of commercially available devices are around 4 Hz. Vibrations below the natural frequency are therefore only registered at a greatly reduced level and the transmission of vibration into an electrical signal is no longer linear, so that the transfer function must be equalized up to 1 Hz. This measure, whether electrical in the analog signal or computational in the digital signal, always contains uncertainties.
We are currently in exploratory discussions with three major subway network operators in Europe to plan the implementation of this project.

At this year's conference "Measuring in Geotechnics from February 21-23, 2024 at the Institute of Geomechanics and Geotechnics of TU Braunschweig, the Competence Center of Distributed Sensing presented a lecture on "30 years of fiber optic measurement technology in geotechnics". Together with the mentor and consultant Klaus Dietz we presented our own wealth of experience in fiber optic measurement technology from the Fiber Bragg Grating to Distributed Sensing.
The exciting discussions with experts from industry, authorities, research institutes and engineering offices after the presentation showed that Distributed Sensing in geotechnics is no longer at the beginning of its application, but is now a renowned technology. Additionally there was particular interest in the topic of distributed acoustic sensing.

On February 22 and 23, 2024, the symposium "Measurements in Geotechnics" will once again take place at the TU Braunschweig. The Competence Center of Distributed Sensing, in collaboration with Stump-Franki Spezialtiefbau GmbH, has submitted a presentation on the topic of "30 years of fiber optic measurements in geotechnics". The lecture will present the development of single-point sensors from the 1993s to distributed sensing today. Currently, fiber optic measurement technology is increasingly finding its way into geotechnics and is beginning to replace conventional sensors. The limits and possibilities will be presented and the current state of requirements will be critically and constructively examined. Not only Distributed Strain Sensing and Distributed Temperature Sensing are discussed, but also Distributed Acoustic Sensing. In addition, the highly dynamic measurement with single-point sensors for dynamic pile test loads will also be presented. So be curious, we will keep you up to date on the details of the lecture "30 years of fiber optic measurements" on CC News.

Recently, the time had come in Vienna! After long constructive preliminary discussions on the technical feasibility we installed five fiber optic extensometers based on Distributed Strain Sensing (DSS) with lengths of up to 45 m at the DC-Tower in Vienna. The aim is to compare the static assumptions based on the calculation of the obtained measurement results. Our work was additionally monitored by ACIMonitoring from Graz.

What is special about our customized and adapted DSS measurement concept? Based on our experience, we have provided a cost-effective variant to split the measurement results with respect to their physical components. This can be necessary as soon as the measurement strings will be not in a permanent thermal equilibrium.

We would like to thank our partner Porr for the trust placed in us and look forward to further good cooperation.

During the recent 17th Hans Lorenz Symposium (HLS) the Competence Center for Distributed Sensing together with the company Stump-Franki Spezialtiefbau GmbH presented new findings and measurement results regarding Thermal Integrity Profiling (TIP) on deep piles with special shapes using Distributed Temperature Sensing (DTS). These include new results on the effects:

- of thermal radiation absorption on the detected pile cubature in relation to concrete technology problems,

- of thermal radiation absorption on the unavoidable skewness (manufacturing tolerances) of the piles, and

- the benefit of the absolute temperature development per measuring strand from the radial hydration heat development on the evaluation of strain measurements over the pile shaft.

In contrast to conventional measurements with single-point temperature sensors, the use of distributed temperature sensing and the associated cost-neutral increase in the number of measurement points made it possible to additionally simulate the setting behavior using the COMSOL Multiphysics® simulation software. The online display of the measurement results realized by DTS enables an early overview of the pile condition with regard to the geometric dimensions as well as the concrete technological boundary conditions at any time. The presented economic advantage of the measuring method of approx. 50% compared to the conventional measuring method shows the performance of the method under monetary aspects.