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Headrace tunnel for HPP Dabar: Breakthrough between the excavation points 3 and 4 achieved

Aug 4, 2020

On Sunday, July 26, 2020 at 10 a.m., a breakthrough was achieved between the excavation points NM3 and NM4. This, in engineering terms, very important event, marked the physical connection of tunnel pipe excavated from the direction of the access tunnel “Straževica” in the total length of l=3,995.5 m with the tunnel pipe excavated from the direction of “Vodostan” in the total length of l=3,857.0 m.

The length of the excavated tunnel pipe downstream from the access tunnel “Straževica” is l=7,852.5 m, and upstream it is l=2,282.0 m, which makes the total continuous excavated length of the tunnel pipe of l=10,134.5 m.

The excavation of a tunnel pipe of such a significant length is a construction accomplishment worth of attention and respect in a broader sense. In order to achieve that, the works were performed simultaneously at four excavation points, in two and three shifts, with daily engagement of up to 250 workers and specialized construction machinery. The condition of the excavation according to the excavation points (NM) on July 26, 2020 is as follows:

  • the excavation point 1 (NM 1) – from direction of access tunnel:   l =    275,5 m;
  • the excavation point 2 (NM 2) – upstream to the access tunnel Straževica:  l = 2.282,0 m;
  • the excavation point 3 (NM 3) – downstream from the access tunnel Straževica: l = 3.995,5 m;
  • the excavation point 4 (NM 4) – upstream from the access tunnel Vodostan:   l = 3.857,0 m;

  • TOTAL: L = 10.410,0 m

Current works:

The excavation of the remaining part of the tunnel between the excavation points NM1 and NM2 in the length of l=1,715 m continues, as the construction of a reinforced concrete lining on the excavated part of the tunnel pipe begins.

Works on the construction of a reinforced concrete structure of the intake structure through which the water from the accumulation “Pošćenje” will be introduced into the headrace tunnel are in progress.

After the earth excavation for the intake structure was completed on July 31, 2020, the reinforcement-concrete works started in the following planned scope:

  • concrete placement (MB30 ,V4, M100) – approximately 7.000 m3,
  • reinforcement placement – approximately 530 t.

The main characteristics of headrace tunnel for the future HPP Dabar:

  • length l= 12,125.00 m;
  • altitude of the start point of tunnel H=813.00 m;
  • altitude of the end point of tunnel H=787.06 m;
  • longitudinal inclination i=2,139‰;
  • circular cross-section of tunnel clear opening D=4.6 m on the length of l=7,853.00 m;
  • horseshoe cross-section of the excavation height H=5.20 m on the length of l= 4,272.00 m;
  • it is constructed using new Austrian tunneling method.

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