Seismic Design and Analysis Aspects of Large Earth Core Rockfill Dam Located in a Narrow Canyon with Multiple Seismic Hazards

The seismic design and analysis aspects of a large earth core rockfill dam located in a narrow canyon and a site with multiple seismic hazards are discussed as well as the seismic design and performance criteria according to the updated ICOLD guideline on the Selection of Seismic Parameters for Large Dams. The rockfill dam is located in a narrow canyon. At the dam site the following seismic hazards have to be taken into account: (i) ground shaking, (ii) fault movements in the dam foundation, and (iii) rockfalls. Moreover, in view of the high seismicity and the proximity of a large fault, reservoir-triggered seismicity may occur during impounding and the first years of operation of the reservoir. Due to the fact that a major fault is within a distance of about 1.5 km from the dam site, which can produce earthquakes with a magnitude up to 7.5, it is anticipated that movements may also occur along discontinuities in the brittle rock of the dam foundation. These discontinuities are formed by joints, bedding planes, fissures and faults although there exist no active faults in the dam foundation which can produce large earthquakes. The seismic design for ground shaking with peak ground acceleration in horizontal direction of 0.74 g is based on a dynamic analysis of a two-dimensional model of the highest section of the dam and following the conceptual and constructional recommendations of ICOLD guidelines. The design against multiple fault movements of up to 1.5 m is based on the requirement that after any movement in the dam foundation or of slope movements through the dam core, at least 50% of the filter and transition zones are still active. Furthermore, the filters are widened towards the abutments. Finally, rockfall is a challenging issue at the dam site as it can affect all components of the project including dam body, including power intake, intakes and outlets of the bottom outlets and the spillway, the penstocks, surge shafts and the powerhouse. The special seismic design features of a rockfill dam located in a narrow canyon are also discussed.