HEARTBEAT OF CLEAN ENERGY

The development of the Kárahnjúkar Hydroelectric Power Station, Iceland,  entails the harnessing of the glacial rivers Jökulsá á Dal and Jökulsá i Fljótsdal. These rivers both originate in the north-eastern region of the Vatnajökull ice cap and run in a north-easterly direction through the Jökuldalur and Fljótsdalur valleys to their common estuary in the Héradsflói bay.

This is the heart of Iceland’s largest-ever industrial development; a EUR 1.1 billion hydroelectric power plant that took five years to build and required the construction of 73 kilometers of tunnels and five dams for three reservoirs – one of the dams being amongst the largest concrete-faced rock-fill dams in the world.

RENEWABLE AND EMISSION-FREE ENERGY

For Iceland, the Kárahnjúkar Hydropower Project paves the way for economic diversity through renewable and emission-free energy. Aluminium is produced by an electrolytic process from bauxite as basic raw material. Electric power represents 20% to 40% of the cost of producing aluminium. Smelters tend to be situated at harbors and where electric power is not expensive. Due to the diversification and availability of clean energy from hydro- and geothermal power plants Iceland has become an important country for the production of aluminium.

WATERTIGHT CONSTRUCTION OF FIVE DAMS

The structures included the Hálslón Reservoir and Dams, the Ufsarlón Reservoir and Dams, the Headrace Tunnel and Penstocks and the Underground Power Station. The fill material of the five dams has a total volume of approximately 13.6 million cubic meters, which had to be prepared on site, then placed and compacted to achieve a watertight construction (see project documentation).

The headrace tunnels were mostly excavated using a “full-face” tunnel boring system (TBM) with a diameter of 5.5 – 7.2 meters; the others were built using the “drill and blast” method for cross sections of 5.8 × 5.8 meters and 7.2 – 7.6 × 8 meters.

SHOTCRETE ADMIXTURES ENSURE PERFORMANCE AND QUALITY

A minimum 250 millimeter thick layer of shotcrete using Sigunit accelerator was applied throughout the drives with additional rockbolts, steel ribs and even thicker layers of shotcrete applied in zones of more difficult geological conditions. For all of the concrete on the project Sika admixtures were used to ensure consistent performance and quality.

Under the prevailing harsh Icelandic environmental conditions the shotcrete admixtures Sika® Sigunit®-L53 AF (IS) and Sika® ViscoCrete®-SC 305 were also used to maintain the pumpability of the shotcrete. The sprayed concrete application equipment selected by the contractors included eight Sika Putzmeister spraying systems Sika®-PM, plus three Sika® Aliva® shotcrete machines and pumps that were installed on the three Hardrock Robbins TBM’s. For the mass concrete on the dams the water reducing plasticiser Sika® Plastiment® LA -100 was used.

SHOTCRETE SET ACCELERATOR FOR EXTENDED STORAGE LIFE

The presence of Sika Concrete Technicians on site throughout the construction period provided all of the concrete technology and technical
support required by the contractors. Due to the remote site location with complex logistics, for long winter periods materials could not be delivered regularly to the project. Therefore the shotcrete set accelerator selected was a highly soluble powder type which provided an extended storage life and could be dissolved in water and made ready to use on site.

USED SIKA PRODUCTS

  • Sika® Sigunit®-L53 AF (IS)
  • Sika® Sigunit®-P1 AF
  • Sika® ViscoCrete®-SC 305
  • Sika® Plastiment® LA-100
  • SikaFiber® 65/35
  • Sika®-PM-400 – Sika-Putzmeister spraying systems
  • Sika® Aliva®-278 shotcrete pumps
  • Sika® Aliva®-403 accelerator dosing unit
  • Al-285 rotor machines
  • Sika® Aliva®-504 sprayed concrete machines