Page - 742 - in Book of Full Papers - Symposium Hydro Engineering

JCSS, "Probabilistic Model Code", 2015, Table 2.1.1, recommends a coefficient of variation of 0.04 on self-weight. This corresponds to a load factor of 0.96, which imply a reduced self-weight from 24 to 23 kN/m3. The correlation between a load factor of 0,96 and the FoS are shown in the table below. Table 4. Correlation between load factor and FoS. Load factor FoS Sliding 0,96 1,08 (=1/0.93) Overturning 0,96 1,04 (=1/0.96) A graphic presentation of the correlation between self-weight and FoS is shown below (blue line = sliding; orange line = overturning). Fig. 5. Load factor (x-axis) vs. FoS (y-axis) when the friction angle = 40º The dam geometry also represents an uncertainty, which also can be illustrated by variating the self-weight. However, probabilistic analysis carried out on a gravity dam in Norway indicate that deviations in the geometry do not have a significant effect on the FoS. PORE PRESSURE The pore pressure represents an uncertainty that can be difficult to predict and therefore difficult to quantify in terms of a specific FoS. This would imply that the pore pressure should be subjected to a relatively high FoS to take account of the uncertainty it represents. In Norway, requirements for stability against overturning assume that the resultant force is within the central dam foundation. Thereby, a linear decreasing pore pressure can be assumed as there is pressure throughout the entire dam foundation. In addition, a check of accident load is required, where the resultant force should be upstream 1/6 of the dam foundation. In this case, full pore pressure can be assumed on the upstream half of the foundation (where there is no pressure on the foundation) and then linearly decreasing to the downstream side. The assumptions for design loads and accident loads are shown in the following figure. 742