TRENCHLESS | SMALL DIAMETER TBM/PIPEJACKING
Above left, figure 13: Tunnel boring machines installed in thrust pit Above right, figure 14: Jacking plates on thrust pit back wall Weekly meetings took place between the detailed
designer and flood modelling/consents team to confirm that any design changes would not affect the modelling/ consenting process. The timescales for the Environment Agency reviewing the flood modelling and consent were such that a number of design choices had to be set in the detailed design ahead of the finalisation of the detailed design.
REINFORCEMENT AND TEMPORARY WORKS The reinforcement design between temporary works and permanent works had to be carefully planned to allow seamless integration during construction. Various techniques were used and one of the most critical was splitting the reinforcement into stage 1 and stage 2. The first stage was everything required for the jacking and thrust pit works ahead of the pipejacking. The second stage included the final structure once the sheet piles were extracted. The splitting of this design into two stages allowed for procurement of relevant materials to
allow for the construction of the culverts as well as fully integrating the pipejacking stage into the permanent works. To provide a clear working area, reinforcement
couplers and stop ends were used to connect the Stage 1 and Stage 2 reinforcement. This prevented reinforcement laps from being exposed during the jacking works. Figure 9 and Figure 10 show the temporary works required during the construction of the thrust pit. Props were installed between the temporary sheet piles whilst the concrete walls and base slab were cast. The propping system was later removed to allow the installation of the small diameter TBMs. A clash was identified between the vertical B20 L
bars in the slabs and wall interface and the propping system during a construction review meeting. To prevent delays to the pour of the slab, an appropriate lap length calculation was undertaken that allowed the existing bars to be cut around the props and additional straight bars provided to lap onto once the propping
Above left, figure 15: View towards reception pit from thrust pit Above right, figure 16: Construction works during possession 16 | September 2024
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