Wechselwirkungsverhalten von thermisch beanspruchten Rohren und zeitweise fließfähigen, selbstverdichtenden Verfüllbaustoffen

authored by

Dominik Wolfrum

supervised by

Martin Achmus

Abstract

The presented thesis is about the investigation of the interaction between Temporarily Flowable Backfill Materials (abbreviation: TFB) and buried, thermally stressed pipes and the developement of a calculation method the load-bearing behavior of the pipes can be described more precisely. Thermally stressed pipes include district heating pipelines and transmission lines for high DC voltages. Knowledge of the resistance to temperature-induced axial pipe displacement is essential in order to estimate the displacements, as well as the normal force distribution along the pipes. The resistance to displacement is investigated in the laboratory, using specially developed small-scale tests, and is presented depending on the specimen age and normal stress. Since the normal stress has an influence on the magnitude of the resistance, a large-scale test is carried out to conclude from the radial temperature expansion of the pipe to the contact normal stress change. A fiber-optic measuring system is used in the large-scale test as well as in the smallscale laboratory tests to determine the expansion or compression of the pipe and the TFB. It is concluded from the tests that, compared to non-cohesive soils, adhesive forces occur between the pipe and the TFB, which lead to significant resistance to displacement. Since there are currently no regulations or scientific studies to reliably dimension a thermally stressed pipe, which also take into account adhesive forces on the contact surface, it is not possible at the moment to dimension pipes buried in TFB. In this work the load-bearing behavor of such pipeline systems is examined and the basics for the design are created. From the small-scale laboratory tests, the large-scale test and numerical investigations, the contact behaviour is analysed and the interface-resistance-characteristics is developed that shows the resistance to displacement as a function of the axial pipe displacement. With this interface-resistance-characteristics, a rod-spring based system and a semi-analytical calculation method are developed to allow the calculation of the normal forces and displacements of buried, thermally stressed pipes.

Organisation(s)

Institute of Geotechnical Engineering

Type

Doctoral thesis

No. of pages

273

Publication date

2021

Publication status

Published

Sustainable Development Goals

SDG 7 - Affordable and Clean Energy

Electronic version(s)

https://doi.org/10.15488/10904 (Access: Open)