TECHNICAL | SOFT GROUND TUNNELLING
While tunnelling through sand can be relatively
fast, there is a risk of water and sand ingress into the tunnel, which, in severe cases, could lead to tunnel collapse. Such incidents have occurred in Bangkok in past projects. Therefore, the TBM design and tunnelling team must exercise particular caution and implement necessary precautions.
SHAFT CONSTRUCTION Five shafts are being constructed, each approximately 40m deep, functioning as launch, receiving, or intermediate shafts. These shafts are constructed using two methods:
D-Wall and Caisson Sinking, respectively, depending on site conditions and construction constraints. For example, shafts built beneath flyovers, where low headroom is a concern, have been constructed using the D-wall method which requires specialised machinery such as baby grabs. Below are the details of various shafts, their dimensions, construction methods, and uses: ● Shaft 9B-1: Rectangular 16m x 13m, D-Wall, Launch Shaft
● Shaft 9B-2: Rectangular 10m x 10m, D-Wall, Intermediate Shaft
● Shaft 9B-3: Circular ID 8m, Caisson Sinking, Receiving Shaft
● Shaft 9B-4: Rectangular 9m x 6m, D-Wall, Intermediate Shaft
● Shaft 9B-5: Circular ID 13m, Caisson Sinking, Launch Shaft
TUNNELLING The tunnelling process is divided based on the size and distance of the tunnels.
TBM 2 Work commenced with TBM 2 (Terratec’s S105 machine, 4.39m-diameter), at Shaft 9B-5. Driving from this launch shaft, the TBM will excavate through the intermediate Shaft 9B-4 and continue on to Shaft 9B-3, the receiving shaft.
TBM 1 Top:
Flyover foundations had to be passed by TBM 1 driving a short S-curve alignment between shafts 9B-1 & 9B-2
Centre and right:
Using D-Wall construction to prepare Shaft 9B-2 for TBM reception below the flyover
TBM 1 (S106 machine, 4.39m-diameter) started its tunnelling operations at Shaft 9B-1, to tunnel through 111m to Shaft 9B-2, and the contractor will then relocate facilities to Shaft 9B-2 to continue boring toward Shaft 9B-3. For the deployment of TBM 1 at its launch shaft,
located between sections of a motorway flyover, the contractor utilised a 500-tonne mobile crane and a 220-tonne crane. Due to limited space for crane manoeuvrability, a special technique was employed by constructing a temporary platform over the shaft, which allowed the TBM to be positioned between the two cranes and lowered into the shaft. The tunnelling operation from Shaft 9B-1 to Shaft
9B-2 also presented challenges for the surveying and navigation system, as the tunnel passes in close
20 | November 2024
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