TY - CHAP A1 - Wolfrum, Dominik A1 - Neidhart, Thomas T1 - District heating pipes buried in Temporarily Flowable Backfill Materials T2 - Energy Procedia N2 - It is state of technology in district heating systems to use sand as backfill material for district heating pipes (DHP). In conventional pipeline construction, Temporarily Flowable Backfill Materials (TFB) have been already used for backfilling the pipe zone. TFB consists of the excavated material, cement, water and optionally bentonite. Environmental and economic advantages are that the excavated material can be reused and that TFB requires no compaction. In order to embed district heating pipes in TFB, soil mechanical parameters of the TFB are required. Above all the resistance to temperature-induced axial displacement should be well-known in order to estimate the displacements of the DHP, as well as the stress distribution along the DHP. Compared to sand as a non-cohesive backfill TFB have remarkable adhesive contact stresses which result in considerable resistance forces.In this article, the contact behavior between TFB and DHP is described as well as the effect on the DHP statics. Therefore, the results of various laboratory tests are summarized and presented to understand the interface-resistance-characteristics (IRC) of the DHP/ TFB interface. Then, the deduced IRC was implemented in a computer program for some comparative calculations with sand and TFB. Finally, the results of cyclic loading are presented and discussed. KW - ZFSV KW - pipe static KW - thermal expansion KW - Temporarily Flowable Backfill Material KW - buried pipeline KW - Fernheizung KW - Rohrleitung KW - Statik KW - Wärmeausdehnung KW - Füllstoff Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:898-opus4-276 UR - https://doi.org/10.1016/j.egypro.2018.08.181 VL - 149 SP - 170 EP - 178 ER - TY - CHAP A1 - Pankrath, Holger A1 - Gömmel, Roland A1 - Alber, D. A1 - Neidhart, Thomas T1 - Stabilising Columns – design recommendations T2 - XVI Panamerican Conference on Soil Mechanics and Geotechnical Engineering, Cancun, Mexico, 17. - 20.11.2019, TC205-meeting Y1 - 2019 PB - IOS Press ER - TY - CHAP A1 - Gömmel, Roland T1 - Numerical investigation of the failure behaviour of a passively laterally loaded rigid inclusion in PLAXIS 3D by means oft he shotcrete-model T2 - European Plaxis-User's Meeting, 17. - 19. Mai 2017, Bauer Spezialtiefbau, Schrobenhausen Y1 - 2017 ER - TY - CHAP A1 - Wagner, Bernd A1 - Neidhart, Thomas T1 - A new backfill material enhancing axial bedding of district heating pipes T2 - Energy Geotechnics - Proceedings of the 1st International Conference on Energy Geotechnics, ICEGT 2016, Kiel, Germany, 29-31 August 2016 N2 - District heating cost reduction efforts are amongst others focusing on the use of a new backfillmaterial. The OTH.R is investigating this material in regard to the engineering of buried district heating pipes.The main focus of this soil-structure interaction problem is axial bedding to reduce thermal induced elongations.The backfill material is characterized and an axial non-linear spring-based calculation method is described.Centerpiece of the method is the contact-working-resistance-line (CWRL).A new Rod-Shear-Test based testingdevice Re-SIST to investigate the CWRL for the new backfill material is presented. The investigated CWRL isdescribed and compared to the CWRL for sand, which is the conventional backfill material. Solutions using thespring-based calculation method are presented and a comparative example of calculation shows the differencein axial bedding when the new backfill material is used. Y1 - 2016 SN - 978-1-138-03299-6 U6 - https://doi.org/10.1201/b21938 SP - 105 EP - 112 PB - CRC Press CY - London ER - TY - CHAP A1 - Hallas, Martin A1 - Hinrichsen, Volker A1 - Neumann, Claus A1 - Tenzer, Michael A1 - Hausmann, Bruno A1 - Gross, Detlev A1 - Neidhart, Thomas A1 - Lerch, Maximilian A1 - Wiesinger, Doris T1 - Cigré Prototype Installation Test for Gas-Insulated DC Systems - Testing a Gas-Insulated DC Transmission Line (DC-GIL) for ±550 kV and 5000 A under Real Service Conditions T2 - 2020 CIGRE Session, CIGRE e-Session 48: Paris, France (virtual), 24.08.-03.09.2020 N2 - More and more generation facilities are installed far away from the load centers. Thus, long distance transmission is demanded, and with this regard DC transmission systems are of special interest. Transmission by overhead lines is a well-proven technology, but due to environmental concern and political decisions underground transmission systems are often requested. Besides DC cables, DC GIL are an interesting option. They enable transmitting high power by only one system in a small corridor only a few meters wide. GIL can be laid in a tunnel or directly buried in the soil. Meanwhile a lot of service experience has been collected with AC GIL technology, but no service experience is yet available with DC GIL. To close this knowledge gap and to investigate the long-term performance, a ±550 kV DC GIL prototype with a current carrying capacity of 5000 A is currently investigated in a HVDC test facility, both in directly buried and in above-ground installation. The test procedure follows the recommendations for long-term testing of gas-insulated systems, currently under preparation by Cigré JWG D1/B3.57. This report describes the test sample arrangements, the high-voltage and high current test equipment and the commissioning procedure for the DC GIL. It illustrates the UHF PD monitoring system installed and the method to identify possible PD defects. The investigated DC GIL is subdivided into two parts: While an above-ground installation is simultaneously stressed by voltage and DC current, a directly buried part of the DC GIL is stressed with DC current only in order to investigate soil mechanics, the temperature distribution in the GIL and in the soil as well as the performance of the backfill material. The report also presents first results gained on the directly buried arrangement for studying the soil mechanics. Y1 - 2022 U6 - https://doi.org/10.26083/tuprints-00014132 PB - CIGRE CY - Darmstadt ER - TY - CHAP A1 - Lerch, Maximilian A1 - Neidhart, Thomas A1 - Bubenicek, Michal T1 - Fibre optic instrumentation of vibro concrete columns and surrounding ground for static and dynamic load tests T2 - Zbornik Radova GEO-EXPO 2020: Proceedings - Scientific and expert conference GEO-EXPO 2020 N2 - Instrumentation of full displacement pile like elements – at Keller called as vibro concrete columns (VCC) – is practically impossible due to utilisation of heavy deep vibro technique during the production and absence of any steel reinforcement. Thanks to cooperation between Keller and Faculty of Civil Engineering of OTH Regensburg a special procedure for post-instrumentation was developed that allows for the axial strain measurement in VCC during the loading tests. The instrumentation comprises among others optical fibre components. The procedure has been deployed on a test site during static as well as dynamic load tests. There were two different types of instrumentation implemented according to art of the load tests. Further there were robust piezometers installed in the soil in advance next to the VCC that allowed for continuous pore water pressure measurements during the load tests. Purpose of the instrumentation deployed is above all to obtain data for effective design of VCC. Y1 - 2020 U6 - https://doi.org/10.35123/GEO-EXPO_2020_6 SP - 40 EP - 49 PB - Društvo za geotehniku u Bosni i Hercegovini ER - TY - CHAP A1 - Neidhart, Thomas A1 - Lerch, Maximilian A1 - Wiesinger, Doris A1 - Hallas, Martin A1 - Hinrichsen, Volker A1 - Tenzer, Michael T1 - Long-Term Tests of a DC Gas Insulated Transmission Line (DC GIL) embedded in Temporally Flowable Backfill: Soil-Mechanical and Thermic Interaction T2 - VDE Hochspannungstechnik: ETG-Fachtagung, 9. - 11. November 2020, Online-Veranstaltung N2 - At present DC transmission systems for long distance transmission are of special interest, particularly with regard to transmission systems that proved ability for directly buried installation. Some service experience has been collected with directly buried AC GIL technology, but none with directly buried DC GIL. First pilot projects with directly buried AC GIL were designed conservative regarding the mechanical GIL support and the maximum allowable current. The aim is to optimize the mechanical and thermal design of directly buried DC GIL to offer cost efficient transmission line solutions. Therefore, a ±550 kV DC GIL prototype with a current carrying capacity of 5000 A is currently investigated in a HVDC test facility, both in above-ground installation and a buried installation. This report presents results gained on the embedded installation for studying the soil mechanics and long-term thermic interaction with the backfill material and the adjacent soil. A DC GIL with a total length of 130 m is embedded in a temporarily flowable backfill (“TFB”) as re-use of the excavated soil on site, which minimizes transportation costs and energy use. TFB is characterized by high contact forces that restrain the DC GIL displacements and by stable thermal conductivity, which optimizes the heat transfer. In order to monitor the mechanical soil-structure-interaction (“SSI”), various temperatures and moisture content sensors were installed inside and around the DC GIL, in the TFB and the adjacent soil as well down to 4 m below the ground surface. Displacement and strain sensors measured the elongations and dilatations of the embedded enclosure tube. Compressive stresses caused by restrained displacements are monitored with load cells. A fiber optical cable is used to monitor the temperatures in the aluminum conductor, on top and at the base of the enclosure tube, as well as in the TFB and the sand cover layer and the adjacent soil. The measurements were completed with some single sensors for temperature, moisture content and porewater-tensions which were mainly concentrated nearby the DC GIL in the TFB and the cover layer. During 15 months, several load cycles impact on the embedded DC GIL. Each load cycle consists of a DC current feed of 5000 A for 4 weeks followed by another 4 weeks without current. Since the SSI is independent of voltage stress, this test is carried out with current only. After 4 load cycles only moderate temperatures are monitored at the enclosure tube and in the TFB, much lower as expected. Seasonal effects predominate the temperatures of the TFB, the cover layer and the adjacent soil, while the DC GIL generates only marginal increases. Moisture contents and porewater-tensions remain constant apart from some variations caused by rainfalls and vegetation cover. The elongation of the enclosure tube is shorter than 5 mm and the forces are lower than 500 kN. It can be concluded that the DC GIL with a current carrying capacity of 5000 A DC embedded in TFB shows temperature-rises far below the technical GIL limits after 4 load cycles. The TFB ensures high and stable heat conductivity and contact forces, thus restraining the GIL movement. The temperature-rises of the natural soil due to GIL heating are comparatively low in comparison to other effects like sun radiation. The TFB shows a good thermal and mechanical performance. KW - Aluminiumleiter KW - Dauertest KW - Deckschicht KW - Dilatation KW - Energienutzung KW - Erdaushub KW - Erdoberfläche KW - Gelände KW - Gleichstromübertragung KW - Installation KW - Kontaktkraft KW - Lastwechsel (Lastspiel) KW - Pilotprojekt KW - Prüfanlage KW - Regen KW - Strahlung KW - thermische Leitfähigkeit KW - Tragfähigkeit KW - Übertragungsleitung KW - Vegetation KW - Verfüllmaterial KW - Wärmeübertragung KW - Wiederverwendung Y1 - 2020 UR - http://www.vde-verlag.de/proceedings-de/455353085.html SN - 978-3-8007-5353-6 SP - 518 EP - 524 PB - VDE-Verlag CY - Berlin ET - CD-ROM ER - TY - CHAP A1 - Koch, H. A1 - Imamovic, D. A1 - Lutz, B. A1 - Neidhart, Thomas A1 - Rogler, R.-D. T1 - High power underground transmission for HV DC T2 - CIGRE Session 46 : from 21 till 26 August 2016 Y1 - 2016 UR - https://cigre.es/wp-content/uploads/2016/08/call-for-papers.pdf PB - CIGRÉ CY - Paris ET - 1 DVD-ROM ER - TY - JOUR A1 - Wagnar, B. A1 - Neidhart, Thomas A1 - Siedentopf, W. A1 - Weidlich, Ingo A1 - Schleyer, A. T1 - Project in the Europaviertel in Frankfurt: Extensometer measurement technique for the quality assurance of the district heating pipelines embedded in temporarily fluid self-compressing construction filling materials JF - Euroheat and Power/Fernwärme International T2 - Projekt im Europaviertel Frankfurt: Extensometermesstechnik zur Qualitätssicherung der in ZFSV gebetteten Fernwarmeleitungen Y1 - 2013 UR - https://www.scopus.com/authid/detail.uri?authorId=55875881100#disabled VL - 42 IS - 12 SP - 35 EP - 39 ER - TY - JOUR A1 - Wagner, Bernd A1 - Neidhart, Thomas A1 - Weidlich, Ingo T1 - Initial findings of the research project: Contact behavior of temporarily fluid, self-compacting backfilling materials and HDPE JF - Euroheat and Power/Fernwärme International T2 - Erste Erkenntnisse des Forschungsvorhabens: Kontaktverhalten von zeitweise fließfähigen, selbstverdichtenden Verfüllbaustoffen und PEHD Y1 - 2013 VL - 42 IS - 10 SP - 26 EP - 29 ER - TY - GEN A1 - Spirkl, Florian A1 - Neidhart, Thomas T1 - Environmental advantages and recycling potential of temporarily flowable backfill as bedding material for district heating pipes T2 - 19th International Symposium on District Heating and Cooling, 07-10. September 2025, Genk, Belgium N2 - District heating networks are a key to a successful transformation towards climate neutrality. Typically, District Heating Pipes (DHP) are embedded in coarse sand with specific grain size distributions and soil properties. An alternative to this are the temporarily flowable backfill materials (TFB). These are a mixture of aggregate, binder (e.g. cement), water and, if necessary, additional supplements, e.g. bentonite. TFB can be mixed-on-site or mixed-in-plant, depending on the boundary conditions. Where possible, the excavated soil is used as aggregate. This paper will look at possible environmental advantages as part of a life cycle assessment, especially regarding the carbon footprint, if TFB is used in place of typical sand bedding. A total of 7 environmental impact factors are compared as part of a case study. As there are a multitude of variables with widely ranging impact for the calculation of the environmental impact, an additional sensitivity study was performed, to determine key parameters for the carbon footprint. In a multitude of cases, it can be shown that TFB has a smaller carbon footprint compared to sand bedding, as the number of transports can be greatly reduced and the TFB doesn’t need to be compacted. These factors predominate the need of cement, which is negatively connoted regarding the environmental impact. If the excavated soil is not eligible as an aggregate for TFB, an alternative base component is necessary. Typically, mixed-in-plant-produced TFB uses sand, as the properties of TFB based on recycling materials has hardly been investigated. In order to conserve natural resources and at the same time recycle construction waste, investigations were carried out into the production and strength behavior of TFB made from different construction materials. The main goal was to mix TFB which is easily re-excavated, as per German guideline H ZFSV. This was achieved with every recycling material, but with varying amount of cement necessary. As part of a long-term study, a delayed increase in strength depending on the source material could be shown. This is due to pozzolanic reactions. Y1 - 2025 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:898-opus4-85111 ER - TY - CHAP A1 - Wagner, Bernd A1 - Hay, Stefan A1 - Neidhart, Thomas A1 - Spirkl, Florian A1 - Ried, Michael A1 - Zrenner, Louis A1 - Weidlich, Ingo A1 - Gabriel, Eugen A1 - Banning, Timo ED - Vanhoudt, Dirk T1 - TFSB as Bedding Material in District Heating Pipe Constructin - Scientifically Proven Long-Term Experience T2 - Proceedings of the 19th International Symposium on District Heating and Cooling; 2025, Genk (Belgium) N2 - Following the explanation of the increasing importance of alternative backfill materials like TFSB, TFSB and their status in terms of science and technology are depicted. Selected results of the research project FW-ZFSV 4.0 are presented: computer-aided static calculation, in situ long term loading of district heating pipes in TFSB and sand, quality assurance and resource conservation. The conclusions provide an overall assessment of the use of TFSB in district heating pipe construction. Y1 - 2026 SN - 9783032098443 U6 - https://doi.org/10.1007/978-3-032-09844-3_10 SP - 99 EP - 108 PB - Springer CY - Cham ER -