TRENCHLESS | SMALL DIAMETER TBM/PIPEJACKING
Above left, figure 8: Proposed arrangement of culverts Above right, figure 9: East Thrust pit Seismic geophysical surveys captured the depth and
extent of the peat and soft clay. Shear waves (S-waves) from the survey demonstrated the presence of a buried sinkhole feature, whereby dissolution within the bedrock resulted in the soils above (alluvium and peats) having collapsed into the location (Figure 6). This feature is likely to be causing the structure and embankment to displace vertically. The dark blue colouration in Figure 6 shows a
distinct area of slow S-wave velocities in a cone shape, indicating the buried sinkhole feature. In Figure 7, more competent strata can be seen for the higher S-wave velocities, shown in the lime green band, indicating a deep feature of compressible soils at the location of the existing structure. As a result of the poor ground conditions, the new
structure was moved 60m north to where more favourable ground conditions were identified by ground investigation.
PROPOSED STRUCTURAL ARRANGEMENT The new culvert structures comprise three 1.8m-diameter concrete pipes, 18.4m long, located to the north of the existing culvert. Their total cross sectional area matches that of the existing brick culvert, as required from the flood modelling undertaken by Aecom., which means future flood events will remain closely related to past events, including facilitating flood balancing either side of the railway embankment. Spacing between the pipes was set out to prevent overlapping settlement/heave during installation. This assessment was undertaken by Active Tunnelling in the early contractor involvement phase. The TBMs began in the thrust pit located on the East
side of the railway embankment and were received in the reception pit opposite. The placement of the pits was aligned with available possessions, with the Normanton (east) being tunnelled under initially to coincide with the first part of the possession plan.
Above, figure 10: East Thrust Pit temporary works 14 | September 2024
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