The Sylvenstein reservoir lies on the northern foothills of the Alps, around 60 km south of Munich. The dam protects against flooding and regulates the minimum water level of the river Isar while also supplying two power plants. Weilheim water authority decided to revamp the dam to ensure its structural stability for future generations. CDM Smith was commissioned with the necessary engineering services such as property and structural planning, dam stability analysis and landscape conservation planning as well as site supervision in the 24 Mio EUR project.
A soil cement-filled diaphragm wall drilled adjacent to the existing loam seal now keeps the 180 m long and 42 m high earth-fill dam watertight. The two-phase diaphragm wall milled into the side rock has a depth of 70 m, an engineering first in Germany. A new gallery measuring three metres across at the base of the dam allows leakage monitoring; any seepage will be caught here and led off via drainage piles at 40 m depth. A vertical shaft and a gallery into the rock provide access from both sides.
The construction measures are a technical masterpiece that will have defined new standards.
The Sylvensteinspeicher dam rests on alluvial river sediments consisting of clay gravel and sand from the Isar River. We used finite element calculations in planning the dam reinforcement under these geological conditions and studying the interactions between the structure and its foundation. Stability analysis has confirmed that the approach taken by our team was the ideal solution, keeping the Sylvenstein reservoir dam safe and secure to protect future generations from flooding.