Page - 737 - in Book of Full Papers - Symposium Hydro Engineering

In general, a probabilistic analysis would be suitable to identify these type of uncertainties. Due to a very limited budget, we had to use a different approach to the issue. Our selected method and the results from the calculations are described in this paper. The calculations have been carried out on both concrete gravity dams and masonry dams. For simplicity, this paper only presents the results related to concrete gravity dams with a height > 8 m. 2. REQUIREMENTS FOR DAM SAFETY IN NORWAY In Norway, dam stability is checked for both overturning and sliding. Calculation of the sliding resistance require a safety factor of minimum 1.5 against normal design loads. For accident loads a minimum FoS of 1.1 is applied. If cohesion is included, a higher FoS is necessary. However, as this require documentation by testing, the cohesion is generally never included. Safety against sliding is estimated with the shear friction factor method, where the FoS is generally defined as the following: 𝑆 𝐹 𝑠 𝑙 𝑖 𝑑 𝑖 𝑛 𝑔 = ∑ 𝐹 ℎ𝑜 𝑟 𝑖 𝑠 𝑜 𝑛 𝑡 𝑎 𝑙 𝑐 𝑎 𝑝 𝑎 𝑐 𝑖 𝑡 𝑦 ∑𝐻 ℎ𝑜 𝑟 𝑖 𝑠 𝑜 𝑛 𝑡 𝑎 𝑙 𝑙 𝑜 𝑎 𝑑 = ∑𝑉 tan(𝜙 + 𝛼 ) ∑𝐻 where ф is the fiction angle and α is the inclination of the foundation. Stability against overturning for concrete gravity dams, is acceptable when calculations show that the resultant force is within the central dam foundation, so that it can be assumed pressure throughout the dam foundation. To simplify the output of safety against overturning, the FoS is calculated instead of the eccentricity of the resultant force. Safety against overturning thereby defined as: 𝑆 𝐹 𝑜 𝑣 𝑒 𝑟 𝑡 𝑢 𝑟 𝑛 𝑖 𝑛 𝑔 = ∑𝑀 𝑠 𝑡 𝑎 𝑏 . ∑𝑀 𝑑 𝑒 𝑠 𝑡 𝑎 𝑏 . 3. METHOD AND ASSUMPTIONS The calculations has been based on a computing tool for stability control, developed by Dr. Techn. Olav Olsen. To make the calculations more efficient, a 737