Replacing the Spitallamm Dam: A Concrete Engineering Marvel in the Swiss Alps

High in the Swiss Alps, amidst the unforgiving terrain and relentless winter snows, stands an engineering marvel that’s rewriting the rules of dam construction. The Spitallamm Dam, originally built between 1925 and 1932, once stood tall as one of the world’s first large arch-gravity dams. But age and structural issues cast a shadow of doubt over its future. How do you replace a massive dam perched on a mountain, surrounded by snow for months each year? The answer lies in innovation, determination, and a whole lot of concrete.

A Dam in Need of Renewal: The Spitallamm Dam is nestled in the Grimsel Valley of Switzerland, forming Lake Grimsel, a vital water body for hydroelectric power generation. However, in the ’60s, inspections unveiled a significant structural issue – a vertical separation or “vertical crack” on the lake side of the dam, hinting at potential catastrophic failure in the event of an earthquake.

The Dilemma of Repair: Initially, the plan was to repair the dam by removing the separated material and reinforcing it with high-quality concrete. But this path posed unforeseen risks, including a potential “alkali aggregate reaction” that could harm the concrete in the long run. Plus, sediment accumulation behind the dam complicated matters.

Ingenious Solution: With repair deemed too risky and demolition impractical, engineers embarked on a remarkable journey: building a new dam right in front of the old one. But this wasn’t any ordinary replacement; it was a feat of concrete engineering.

Concrete and Construction:

  1. Double Curvature Design: Unlike the original dam with a single arch, the new dam adopted a double-curvature design, curving both horizontally and vertically. This innovation allowed thinner walls while maintaining the necessary strength, a testament to modern concrete technology.
  2. Explosive Clearing: The construction process began with controlled explosives, clearing space for the new dam. A tricky maneuver considering the old dam was holding back a massive lake.
  3. Staggered Towers: To increase overall dam wall strength, the new structure rose as a series of staggered 15-meter wide towers over four years. This method allowed for efficient curing of each segment.
  4. Tunnel Excavation: A massive tunnel was carved through the mountain to enable water discharge from the reservoir, crucial for managing water levels.
  5. Sediment Management: Teams had to drain the reservoir, clear sediment from the lake bed, and complete tunnel excavation before allowing natural refilling.
  6. New Dam’s Role: The original dam is preserved, while the new dam absorbs the water pressure, ensuring the old dam’s historical significance remains intact.

Overcoming Challenges:

  • The project operates nearly continuously during the summer months to compensate for winter shutdowns.
  • The remote location poses logistical challenges, but an on-site concrete plant using local granite material helps mitigate these issues.

The Power of Hydroelectricity: Lake Grimsel and the Spitallamm Dam are integral to Switzerland’s hydroelectric power generation. The Grimsel Valley houses numerous dams and power stations, showcasing Switzerland’s commitment to clean energy.

Conclusion: The Spitallamm Dam replacement project is a testament to human ingenuity and determination in the face of challenging terrain and aging infrastructure. Through innovative use of concrete and modern engineering techniques, a new dam is rising to secure the region’s energy needs while preserving the legacy of the past. As we look to a future with aging dams worldwide, projects like this offer valuable insights into the possibilities of renewal and the role of concrete in construction’s ever-evolving landscape.

Watch the video on this amazing concrete project here