Page - 1352 - in Book of Full Papers - Symposium Hydro Engineering

Fig. 1: Stress state in the upstream dam shoulder At high reservoir levels, the water pressure acts on the core and provides the upstream horizontal support for the core. The horizontal water pressure on the water barrier leads to high horizontal stress in the core and in the adjacent zones downstream of the core. Since the asphalt concrete core material is impermeable, internal water pressures cannot develop and therefore the effective core stress is equivalent to the total stress upstream the core. Due to this high horizontal stresses during impoundment, the stress state in the core is almost isotropic (σ1~σ3) and the Mohr´s circle is reduced and therefore in a stable stress state far off the failure line. The core and the shoulder are shifted downstream. When the reservoir level is lowered, the horizontal support of the core by the water pressure is lost and a sliding wedge which developed during the first impounding provides the necessary horizontal support to stabilize the core and the adjacent upstream “braking” zone. It can be seen from deformation measurements of asphalt concrete cores (see Chapter 3), that the back- deformation due to drawdown is only small compared to the initial deformation during impounding. Figure 2 shows the theoretical model of the mobilized sliding wedge for a vertical core and for an inclined core. Fig. 2: Mobilization of sliding wedges for vertical (Feistritzbach Dam) and inclined AC core (Finstertal Dam) During construction, the stress state of the asphalt concrete core depends on the stiffness of the core and the adjacent zones. It is of interest, how the additional 1352