Powerful premiere for D35

In the land of Fjords, the use of hydro power for generating power is a tradition. Norway covers 98 percent of its demand with the renewable energy source and continues the expansion of hydro power. In the Norwegian province of Aust-Agder located about 200 km south west of the capital Oslo, the Otra Kraft company is the owner for the “Brokke Nord og Sør” for the “Skarg Kraftverk” power station. The plan for this project includes construction of a dam in Sarvsjuvet near the town of Bykle where it is to back up the river Otra to a depth exceeding 40 m. After scheduled completion in April 2014 the Skarg power station will be supplied with water. The Norwegian company Kruse Smith was commissioned to construct the Sarvsfossen, a dam that is 150 m long and 50 m high. Doka is the provider of the formwork solution used for the concrete arch dam. The formwork experts’ new Dam formwork D35 came out on top in the bidding process. This project will be the first time the standard system is used; it allows for rapid progress during construction.

Doka developed a formwork solution that focuses on efficient implementation as well as the building site team's safety – a topic of utmost priority for Kruse Smith as well as for Doka. In terms of formwork engineering, the concrete arch dam with its scant structural tolerance of
8 mm per 2 m as well as the dam crest geometry were challenges during the planning process. Moreover, Otra Kraft preferred a solution without formwork ties.

Successful premiere for D35

The newly developed Dam formwork D35 with its anchoring tensile force of 350 kN was virtually predestined for the construction of Dam Sarvsfossen. Using this formwork solution, for the first time it is possible to form blocks that are 5 m high. With this standard system Doka is able to meet the requirements of this project without special constructions or additional measures. This was one of the crucial aspects for Kruse Smith when awarding the contract.

Using Doka Dam formwork such as D35, it is feasible to form single-sided construction projects such as dams and river power stations without formwork ties. The climbing brackets will transfer all pouring loads into the previous pouring section. The use of the spindle strut shoe of the Dam formwork D35 allows for inclination adjustments of up to 37° in both directions. As a result, adapting the system to sloping or kink wall areas is a simple process. As soon as the product innovation was introduced its characteristics garnered enthusiastic reviews: “Continuous formwork planning renders structural alterations of platforms and formwork elements unnecessary”, says Kruse Smith's Construction Manager Thomas Odde. “We are able to quickly reposition climbing brackets as well as formwork for the entire dam using only two cranes. This solution combined with pouring blocks 5 m high allows us to work unbelievably quickly.”

Customised forms

At it's base, Dam Sarvsfossen is 6 m to 7 m thick and tapers to 2.5 m at the top. The concrete arch dam is built according to the “leader-follower principle”. The first step of this process is construction of three blocks referred to as leader blocks which serve as base supports. The second step is mounting the formwork between these blocks and to pour CIP concrete in the follower block. In this project the wall formwork consists of the Large-area formwork Top 50 which can be perfectly combined with the Dam formwork D35. In order to achieve the minimal structural tolerance of 8 mm in terms of formwork engineering, Doka provided the Top 50 elements with the correct radius. In order to do so, the formwork experts produced special moulded plywood which served as a basis for mounting the face sheet.

A specially designed dam crest required by the architect sits atop the structure. For this aesthetic specification Doka experts planned a special design consisting of standard D35 construction kit components. In addition, the short reach of the concrete pump required a custom solution in special sections. We were able to integrate a concrete placing boom into the robust formwork system D35 during the period of pouring.

Logistics and safety are part of the solution

The dam construction consists of 10 pouring sections requiring the use of a total of 104 brackets of Dam formwork D35 and 660 m² of Large-area formwork Top 50. As part of the formwork solution, Doka provided the customer with a logistics plan perfectly matching the use of materials to construction site requirements. As a result, there is no downtime and the construction process is accelerated overall.

Construction site safety also contributes significantly to an efficient construction process. Closed and generously dimensioned working platforms up to 3.60 m wide ensure safe working conditions at every stage. Construction Manager Thomas Odde: “All platform railings are 2 m high; all openings are closed with planking covers. The formwork system is very stable and we feel really safe working on it.”

In this project, employees of the Doka branch in Oslo are working closely with experts from the Competence Centre Power Plants at Doka headquarters in Austria. A Doka formwork instructor provides team support at the construction site and ensures professional instructions for the construction site staff as well as assembly and handling of formwork systems. Apart from that, Project Engineer Roman Katzengruber is available on site during important project stages: “Close cooperation with the customer in all stages of construction is required for a comprehensive formwork concept and thus for successful project progress.”