Project description
The main features of the dam are as follows (see Figure 1):
• Country Switzerland
• Dam type: earth-rockfill with inclined core
• Maximum height: 117 m
• Crest length: 780 m
• Crest level: 2204.0 m a.s.l.
• Maximum base width: 373 m
• Dam volume: 10.6 million m3
• Reservoir volume: 100 million m3
• Surface area of reservoir: 1.76 km2
• Construction period: 1960-67
• First impoundment: 1969
• Designer Poyry Energy Ltd. (formerly Electrowatt Engineering Ltd., Zurich, Switzerland)
• Reference Swiss dams, Monitoring and Maintenance, Section 4.3.3 ‘Mattmark’ by B. Gilg, Swiss National Committee on Large Dams, edition for the 15th International Congress on Large Dams 1985 in Lausanne, Switzerland
Figure 1: Mattmark Dam
The dam is located on top of a morainic layer with a maximum depth of 88 m as shown in Figure 2. The core and the shell of the dam are also made of morainic materials. In the case of the core, coarse-grained components larger than 10 cm were removed and the fill was compacted. The shell was built without any compaction. In order to facilitate the foundation grouting works, an inclined core was selected.
Special features of Mattmark dam
The special features of Mattmark dam, which make it a milestone project, are as follows:
1. The Mattmark dam was the first large embankment dam to be built on top of a deep soil layer (approx. 80 m) consisting of loose lake sediments, alluvial deposits, ground moraine and pre-glacial deposits, all of these quite pervious.
2. With a height of 117 m and a crest elevation of 2204 m a.s.l., the dam was one of the highest embankment dams in the Alps when it was completed.
Figure 2: Typical cross-section of Mattmark Dam
3. The dam was built in an area with extreme climatic conditions, a hazardous glacier and high seismicity (peak ground acceleration of safety evaluation earthquake: 0.43 g in horizontal direction)
4. The dam was constructed entirely of materials available at the site. The core was produced from morainic material with limitation of the maximum grain size (100 mm) and the shell material from the same material with larger grain sizes (up to 800 mm). The filter and drainage layers were made from the alluvial deposits The dam core is inclined to avoid foundation on the lateral moraine.
5. The construction of the approximately 100 m deep grout curtain in the glacial and post-glacial deposits was a truly exceptional achievement. It comprised 72 km of grout holes in the overburden out of which 49 km were grouted, and 12 km of holes in the granitic-gneissic bedrock. Two kinds of grouts were used, namely a clay-cement grout and a bentonite-silica-phosphate gel.
6. Because of the great depth and the existence of large blocks in the very heterogeneous moraine a cut-off wall would have been highly problematic with the technical means available at that time.
7. Cracks were observed in the core near the right abutment and were caused by relatively high settlements of the foundation, and movements of the core along the abutment contact. The shell material was dumped only, without compaction.
8. Comprehensive soil investigation tests were carried out for the embankment dam materials (including large-scale triaxial tests with diameter of 60 cm and height of 120 cm).
9. The reservoir has been operated successfully since its first impoundment.
This information was compiled from reference by B. Gilg on Mattmark dam (see Attachment) also from: Gilg, B., 1973. Mattmark – A dam founded on alluvial and morainic deposits. In: Foundations for Dams, An Engineering Foundation Conference, Asilomar Conference Grounds, Pacific Grove, CA, American Society of Civil Engineers, New York, pp.215-248.
