A deal to supply all the shotcreting equipment for the 690MW Kárahnjúkar hydroelectric power project, in Iceland, forms the first combined package for the new Sika and Putzmeister manufacturing alliance (T&TI, October 2003, p39). Eleven shotcreting units and all the accelerator and superplasticiser needed for Kárahnjúkar’s 70km of tunnel and cavern excavations are supplied by the alliance.
Under two separate contracts, Impregilo of Italy is constructing the 9Mm³ rock-filled concrete-faced dam at the head of the Hafrahvammar Canyon and almost 60km of 7m diameter TBM driven headrace tunnel, access adits, valve chambers, grouting and drainage galleries, and the surge tunnel. Meanwhile the Hochtief-led Fosskraft JV, with Pihl & Son, Istak and IPC partners of Iceland, is contractor for the powerhouse caverns, two 4m diameter x 400m deep high-pressure shafts, and the 1.4km long tailrace tunnel.
For its tunnelling works Impregilo has taken delivery of eight shotcreting units: four Aliva-500 mobile wet-mix shotcreting machines, an Aliva-504 portable unit with an Aliva 263 Duplo wet or dry rotor pump, and three Aliva-263 Duplo units with ring beam-mounted nozzles on the back-ups of the three Robbins TBMs excavating the 53km long headrace tunnel. Under a separate order, Putzmeister has also supplied a truck-mounted M36 boom pump to Impregilo for placement of in-situ cast concrete.
At the power station site in the Fljotsdalur River valley, the Fosskraft JV has two mobile wet-mix shotcreting units and has taken delivery of the first Sika+Putzmeister prototype. The Sika-PM400P is a low profile, compact mobile designed especially for shotcreting in small diameter tunnels and headings.
Wet-mix shotcreting
More than 100,000m³ of shotcrete is due to be used on the project, the majority of which is steel-fibre reinforced wet-mix. To meet this requirement, the alliance between Sika and Putzmeister is strategic. It combines Putzmeister’s reputation in heavy-duty concrete pump technology with Sika’s leading shotcreting equipment, developed by its incorporated ex-daughter company Aliva. All future dense-stream wet-mix shotcreting units from Sika – now known as Sika Tunneling & Mining or STM – will be equipped with Putzmeister concrete pumps and nozzle booms; with the spraying nozzles, dosing units and PLC-based control systems developed by Aliva.
Climate control
For both contractors at Kárahnjúkar, the affects of the extreme winter weather in Iceland are a major concern. For shotcrete, the aggregate must be kept in steam heated containers, to melt away any ice in the material, before being mixed using bone-dry cement, hot 80ºC water and adding Sika air entrainer and 1% of Sika Viscocrete 3060 IS superplasticiser to sustain workability.
For the liquid accelerator Sika has established a mixing facility in the town of Egilsstadir, where raw material is shipped in via Sika’s Denmark agency to produce the Sigunit alkali-free AF53 accelerator. From the mixing plant, managed by local contractor Malarvinnslan, the liquid accelerator is transported the 100km to the sites in heated containers. Keeping the material heated to about 15ºC is essential, both for preventing the liquid from freezing in winter temperatures of down to -20ºC, and also to help avoid separation of the ingredients. At peak, Malarvinnslan will have to mix up to 15t of raw material/ week to meet on-site demands. All shotcrete, wet or dry, is steel-fibre reinforced at 40kg/m².
TBM shotcreting
On the three Robbins TBM back-up units, Impregilo has the availability of both wet and dry-mix shotcreting via the Dulpo 263 machines, located 30m from the cutterhead. Wet mix is applied for permanent lining and support according to four rock classes, in the otherwise unlined headrace, with dry-mix hand-held application used if support is needed immediately behind the TBM.
Site support and service
For both Impregilo and Fosskraft teams, keeping equipment serviced and available at all times is a critical element in meeting the tight construction period. From award of contracts in March and October 2003 respectively, the two contractors are working towards an agreement with Iceland’s national power company, Landsvirkjun, to have the first two of the power station’s six 115MW units on-line by early 2007 and ready to supply the majority of the plant’s electricity generation to the new aluminium smelting plant currently being developed in Iceland.
Support and service supervision for all Sika-Putzmeister machinery on the project is assigned to the company Kraftvelar, which is also the support and service agent in Iceland for Tamrock and Komatsu. Both contractors are using Tamrock jumbos and drilling units exclusively for all the drill and blast work required by the dam, headrace tunnel and power station excavations and both have a large fleet of Komatsu dump trucks, excavators and loaders.
Servicing equipment in the harsh winter conditions of north-east Iceland is a demanding task. Ensuring that crews remember to air flush all drilling and shotcreting equipment at the end of each cycle, to prevent water freezing in the systems, is a necessity. The task then centres on maintaining adequate stockpiles of spare parts, since delivery of shipments by sea or air freight to Iceland can be weather delayed and road transportation to sites can be cut off for days at a time by heavy snow storms or high wind driven snow drifts.
