TECHNICAL | MINED TUNNELING
TTC box walls
top/bottom slabs
TTC box
Underpinning mined galleries
Bottom slab/soil interface
Above, figure 5: Simulation of the existing TTC box and the completed underpinning galleries
Challenges during Construction
Several challenges encountered during the execution of the works are described in the following sections.
Confined Working Space The biggest challenge in this project was working in confined space under the existing TTC subway box. The contractor faced a very tight environment caused by existing support elements, the steel waler beam, and the subway box itself. This became more challenging once the first needle beams within the galleries had been installed. The prompt and uneventful execution of the works required a skilled construction team equipped with the smallest available plant.
Grout Bags Grout bags were placed between the vertical props and the TTC box to ensure a full connection (see Figure 10).
The grout bags were installed with vertical props and precast concrete pad footings with their connecting beams before applying the first shotcrete layer. With changing weather conditions and colder ambient air temperature setting in, the grout curing time increased significantly.
TTC Box Slab / Mud Slab During the excavation of Gallery 1B an unexpected amount of previously poured concrete underneath the TTC box base slab was encountered, which was not documented in the as-built drawings. This additional concrete appeared also in other galleries and resulted in a significant amount of extra time and work effort. Chipping of the concrete was only permitted by hand
(jackhammer) as directed by TTC. No excavator or similar heavy equipment was allowed due to working beneath the live operating subway.
Total displacement min (stage): 0.000m
max (stage): 0.044m
0.0000 0.0005 0.0010 0.0015 0.0020 0.0025 0.0030 0.0035 0.0040 0.0045
Above, figure 6: 2D FEA galleries Results: Total Displacements 16 | Winter 2023
Joint
Joint
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