On 16th May 2015, contractor, Italian-Thai Development PLC broke through using a TERRATEC 6.44m diameter EPBM into Sanam Chai Station in Bangkok, marking the completion of the excavation of the West Bound MRTA Blue Line Extension Contract 1.
The EPBM bored this 2,800m long alignment in one pass, crossing two unexcavated stations and one ventilation shaft on its way. The next drive along the East Bound alignment of the line will have the stations completed as the TBM arrives, so it will be dragged through them.
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The excavation was through complex geology and in the presence of high ground water pressure. The soil consisted of stiff clay and Bangkok’s aquifer sand, with large gravels and sandstone at deepest part of the alignment.
The TBM drove under a host of historical buildings in the old Bangkok City area. Due to this, very accurate settlement control was essential. The machine was equipped with a 2-Liquid type backfilling system and a special Clay Shock injection system through the shield. This combination proved very effective and restricted the settlement to less than 1cm in those critical areas.
The EPBM had to bore through as many as eight (8) diaphragm walls, as well as several obstacles such building foundation, so TERRATEC selected a unique CutterHead design with a conical shape to overcome these without disrupting the soil around.
The TBM achieved the planned average rates of 18m per day or 82m per week during the boring cycles. Now the TBM is being dismantled and moved to begin the East Bound tunnel by the beginning of August.