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Plastics are macro-molecular, organic connections which are created by chemical juxtaposition of low molecular weight basic components (so-called monomers) [Bos00]. Because of the large numbers of possible juxtapositions (linear, branched, cross-linked), plastics can be deliberately synthesized according to their desired properties into thermoplastics and thermosetting materials. (Image: Schematic view of the structure of plastics according to [Bos00] [… |
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Plastics originating from linear or branched molecule fibres result in thermoplastics that can be repeatedly melted and dissolved and which form the basis of the following:
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(Table: Material properties for PE- and PE-X pipes [Bos00]) |
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(Table: Material properties for PP-HM) (Table: Material properties for PVC-U) |
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May 15, 2020 According to the latest state of the technology and in the absence of an appropriate calculation method, a constant modulus of elasticity is used for the pressure transfer ring in the structural verification process of planning a jacking measure. Due to the inevitable lack of precision this constant has to be chosen on the safe side. Thus, the structural calculation of the jacking pipes can only be a “snapshot“ of jacking, in which only one specific … |
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May 15, 2020 “A chain is no stronger than its weakest link” – if we apply this well-known saying to the chain “pipe string”, the weakest link would be the pipe joint. The central structural issue in pipe jacking is the transmission of jacking forces from pipe to pipe. With pipes made of reinforced concrete or vitrified clay, in particular, the pipe string does not bend continuously in curved jackings and in steering movements, but the “stiff” pipe remains largely … |
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May 15, 2020 The bigger the forces and the number and extent of the steering movements, the more the pressure transfer ring is loaded far beyond its limit of elasticity. This load results in irreversible plastic compressions that persist even after the pressure transfer ring is unloaded. Each pressure transfer ring is loaded and unloaded many times during a jacking measure. Furthermore, the angular deflection changes constantly. Thus, the pressure transfer ring … |
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May 15, 2020 (Image: Typical damages to jacking pipes due to overloading during jacking - Bild 1) (Image: Typical damages to jacking pipes due to overloading during jacking – Bild 2) (Image: Typical damages to jacking pipes due to overloading during jacking - Bild 3) (Image: Typical damages to jacking pipes due to overloading during jacking - Bild 4) (Image: Typical damages to jacking pipes due to overloading during jacking – Bild 5) (Image: Typical damages to … |
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May 15, 2020 A more accurate structural calculation of the pipe stress considering the non-linear stiffness behaviour of the pressure transfer ring is absolutely necessary to ensure a sufficiently high level of safety. The economic practicability must also be taken into account. Essential input parameters for a calculation of the pipe stresses from the engineering viewpoint are:
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May 15, 2020 Jacking pipes have a dual function: they provide permanent support for the excavated cavity and, in the case of single-shell lining, for the pipeline structure. The subject of this module is jacking pipes made of cement-bound materials, vitrified clay, glass-fibre reinforced plastics, polymer concrete and plastics. After completing this module, you will have a sound knowledge of:
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Underground pipelines and utilities are predominantly installed by using the traditional open-cut method (i.e., cut and fill): a trench is dug, the lines are installed by constructing proper embankment or sheeting or using a trench box, and the trench is filled afterwards. In the face of the numerous challenges (e.g., urbanization, densely populated areas) as well as growing environmental consciousness, it is important to consider trenchless technology … |
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