SMALL DIAMETER TBM/PIPEJACKING | TRENCHLESS
Above left, figure 4: Down Leeds west Inlet (4.9m AOD) Above right, figure 5: Up Normanton east Outlet (3.125m AOD)
Lines. The superstructure comprises a pair of brick arches and the substructure has concrete wingwalls and foundations. The structure is owned and maintained by Network Rail and was subject to regular additional monitoring, being undertaken due to significant settlement of the Up Normanton end of the structure. Subsidence had been taking place under the Up and Down Normanton lines since 1940 and this has resulted in increased ballast depths. The headwall on the Normanton side was extended to allow placement of ballast to maintain track geometry. Between the Leeds and Normanton lines there is a
significant fracture and displacement within the walls/ slab (Figure 3). The invert of the culvert on the Up Normanton outlet is 3.215m AOD and on the Down Leeds inlet it is 4.9m AOD; a level difference of almost 1.7m as a result of significant differential settlement along the structure. The Normanton side is constantly under standing water.
EXISTING GROUND CONDITIONS The top of the railway embankment is made up of track bed (ballast, ash and sand) supported by non-
engineered fill that was claimed from the local area during construction. The embankment itself consists of a mixture of coarse and fine deposits. The embankment was originally constructed to
carry two tracks (Leeds lines) and then extended to carry the Normanton lines. This extension appears heterogenous in construction and material and a potential pathway exists between the formation of the embankment materials. Ground investigation (GI) at the embankment was a combination of intrusive and geophysical methods. The GI confirmed the presence of a high plasticity, exceptionally low strength clay with a high organic content (indicating peats). This soil type is highly compressible and therefore is susceptible to settlement. An additional issue within the ground is further
settlement occurring due to dissolution features caused by groundwater moving through the bedrock. This will be an ongoing future issue in the area and future settlement cannot be accurately predicted. This uncertainty combined with the underlying peat means that any structures built at the same location will undergo unpredictable settlement.
Above left, figure 6: Seismic S-Wave velocity (km/s) Above right, figure 7: Map showing base of peat layers September 2024 | 13
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