All-weather Work at Karahnjukar with Heavy-duty Machinery The Vatnajökull glacier in the northeast of Iceland is an area which can only be accessed under great difficulty. In the winter months from October to May, the journey from the nearest town Egilsstadir and from the camps to the construction sites is frequently interrupted by blizzards (see map). Access routes are impassable for hours, sometimes even days. Temperatures can drop to -15 °C. The Karahnjukar hydroelectric power project is being built in this hostile environment. The project involves the use of three Robbins TBMs, Sika-Putzmeister machines and Sika concrete additives in both the construction of the 193 m-high Karahnjukar dam and for shotcrete work in the numerous tunnels and the two gigantic underground chambers.The gigantic hydroelectric power plant is being built to cover the energy requirements of the American Alcoa group for its new aluminium smelter. The state-of-the art plant is being constructed on the east coast of Iceland in the bay at Reydarfjordur which remains free of ice all year round. The investment is forecast to require about EUR880 million. The six turbines in the Karahnjukar power plant with an output of 690 MW will serve the aluminium smelter and must be on-stream by October 2007. Landsvirkjun, the national electricity company, will be later operating the Karahnjukar power plant which is mainly state-financed. Building costs alone amount to more than €1 billion on top of which come investments for developing the infrastructure. Visit www.karahnjukar.isThe Karahnjukar project involves the construction of the 730 m-long 193 m-high Karahnjukrstifla main dam (contract KAR 11) and the 7.2-7.6 m-diameter headrace tunnel (contract KAR 14). Pressurised water is fed on the one hand along the headrace tunnel from the dam to the vicinity of the power plant (a distance of 39.6 km) and on the other hand from the much smaller Usfar reservoir through the Jökulsa tunnel (over a distance of 13.3 km). Both of these contracts are being carried out by Impregilo whose team has been on the site since February 2003. At peak times more than 1,200 employees are working on the two construction sites.The main dam is a rock and gravel construction requiring the installation of a 5-phase crusher plant and an extensive conveyor system. Impregilo used a Putzmeister type BSF 36.14 H truck-mounted concrete pump with a two-layer delivery line for concreting the dam abutment and for lining the dam surface. The wearing surface of this Putzmeister pipe is particularly robust, allowing considerably longer stand-up times. This is an extremely important factor, considering that the concrete aggregates are made of hard volcanic basalt lava. Visit www.putzmeister.de and www.sika.chTo reduce construction time, the headrace tunnel is driven from the dam side and three access adit tunnels (total length approx. 6.9 km). In the meantime, several new concrete mixing plants have been set up in the region of the main dam and at the three access adit tunnels. In addition to the usual types of site-mixed concrete, the mixing plants also produce wet shotcrete reinforced with steel fibres (40 kg/cu m). From the access adit tunnels, Impregilo is driving the total length of the 53 km-long headrace tunnel using three large Robbins TBMs. The steel fibre-reinforced shotcrete is used to ensure safety during driving operations, for the final permanent lining of the headrace tunnel and the three access adit tunnels. Impregilo will be placing a total of around 70,000 cu m of steel fibre-reinforced shotcrete in the various tunnels of the dam.All three TBMs are now fully operational and have broken through the three adit tunnels to begin work on drilling the main headrace tunnel that will carry water from the Halslon reservoir to the powerhouse. The last of the giant machines to breakthrough was TBM 2 on 9th October, 2004. At week 43, progress at the headrace tunnel reached 567 m of 14,067 m (4%) with TBM 1, 268 m of 10,251 m (3%) with TBM 2 and 1,992 m of 5,477 m (36%) with TBM 3. Visit www.robbinstbm.comBesides Impregilo, the Fosskraft JV including Hochtief, E. Pihl & Son, Istak and Iceland Prime Contractor is also playing a decisive role. Their contract (KAR 15) is for the construction of 7.5 m-diameter access tunnels to the 127 m x 14 m x 35 m underground turbine halls and to the neighbouring 103 m x 13.5 m x 15 m transformer hall, two 410 m-high 4 m-diameter vertical headrace tunnels, a 1.3 km-long 9 m-diameter tailrace tunnel and a 1 km-long 4 m-diameter cable tunnel. The machine halls alone require 2,000 cu m of 10,000 cu m fibre-reinforced wet shotcrete and 17,000 cu m of approximately 40,000 cu m structural concrete.Aggregates required for the shotcrete are delivered by truck to the construction site and stored in steam-heated containers in order to prevent the formation of ice in the concrete batches which have been made according to stringent quality standards. The dry material for the shotcrete is prepared using 80°C hot water. The truck mixers must also be carefully freed from any ice prior to loading in order to maintain the correct temperature for the setting of the concrete, even in biting frost. Last winter at the dam construction site, another approach was taken: in exposed areas, the concrete was placed into heated plastic formwork to prevent the concrete from cooling down too quickly. It was also absolutely essential to be able to work on the diversion tunnels during the winter months to guarantee there would be additional diversion capacity to accommodate the enormous masses of water set free in the snow melt in spring 2004.When having to select concrete guns and additives, both Impregilo and Fosskraft selected machines and materials from the Sika-Putzmeister alliance. In addition to fluxing agents and aerating agents, Sika supplies the alkali-free setting accelerating agents. In order to ensure an uninterrupted and efficient supply of the setting accelerator (Singuit AF 53) during the four-year construction period, Sika installed its own mixer unit in the neighbouring town of Egilsstadir. A local company receives the raw materials for the accelerator in powder form, mixes them under controlled temperatures with water to produce a liquid accelerator which is then transported to the construction site in 1,000-litre tanks by truck. The accelerator must then be stored at the different construction sites at a temperature of 15°C. Producing the accelerator locally and according to demand avoids the problem of de-mixing or segregation in the product.The Sika-Putzmeister alliance supplied all of the machinery required for shotcreting operations at Karahnjukar, including several large-scale shotcrete manipulators which have been installed for wet spraying operations in various tunnels as well as in the turbine hall and transformer hall, deep within the mountain. The wet spraying devices are equipped with a smooth-running type BSA 1005 piston pump and a spraying arm which allows work to be carried out up to approximately 16 m high. The telescopic spraying arm has a 3 m sliding arm and a nozzle spray head at the top to provide optimum mobility and efficiency in the interest of high-quality shotcrete application. The top performance of the Sika-Putzmeister wet spraying device is very generously measured at 30 cu m/h. For example, in the tailrace tunnels built by Fosskraft, approximately 120 cu m of wet shotcrete is placed weekly on round lengths of 55 m to provide an extremely even spray pattern. The reason for these relatively small quantities of shotcrete are the stable, geological conditions so that shotcrete reinforcement is only required in the roof between the "10 o'clock" and "2 o'clock" position. The wet shotcrete used in this area also contains about 40 kg/cu m steel fibres.The prototype of Sika's new wet spray device PM400 P is also in operation at the Karahnjukar site. This device was developed specially for application in tunnels with a small cross section, e.g. for the 4 m x 4 m cable tunnel. It is equipped with a Putzmeister piston pump from the BSA 500 series, a Sika spray arm AL 302 and a dosing system AL 403. The AL 403 is fitted with SPC and can be set so that on site, the nozzle guide has very little influence on the dosing of the accelerator which means there is no risk of the quality of the shotcrete being changed due to improper and incorrect setting of the dosing rate. Sika also supplied rotary spray units which are suitable for use for both dry and wet spraying operations. They have been installed on the shotcrete platforms of the three 1,200-ton Robbins TBMs about 30 m behind the drill head usually to lay down wet shotcrete. Dry shotcrete is only sprayed when safety operations using small quantities of concrete must be carried out immediately behind the drill head. The original plan was to stop outside work on the dam during the three most severe winter months but because the 4-year construction schedule is so tight, it is necessary to continue working in shifts throughout the whole year. Work is well within schedule and at some sections, for example the tailrace tunnel, is already six to eight months ahead of schedule. Click is/14. 46/04.