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  Backfilling of 618m Steel Lining VerticalShafts Uma Oya Project, Sri Lanka

  Uma Oya Multipurpose Development Project is a hydropower project comprises of two RCC Dams which their reservoirs are connected by a Link tunnel. The water will transfer from first dam reservoir to the other and then it will transferred through a 15.4 km headrace tunnel to the top of a 618 m deep vertical pressure shaft. This shaft provides high pressure water with its suitable head for an underground powerhouse which is designed to generate 120 MW electricity by two Pelton turbines. In this project, Raise Boring Machine utilized to excavate the vertical shafts including the Pressure Shaft. There was no middle access (adit tunnel) neither during the excavation nor steel lining of the Pressure Shaft. During the shafts pilot drilling and reaming of raise boring, numerous unforeseeable conditions occurred which resulted to a change in the design of the shaft support as well as prolongation of the excavation works with inefficient progress rate.. So backfilling and support shall be done after completion of the steel lining erection and because of material of steel lining and its welding properties the backfill concrete shall not contact with injection hose. This paper review the methodology of backfilling of the 0.5 m distance with 618 m height in pressure shaft by pumping the concrete from the bottom to top with consideration of constraints.

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