Evaluation of 3D Nonlinear Earthquake Behaviour of the Ilısu CFR Dam under Far‐Fault Ground Motions

Abstract

In the recent times, many huge concrete face rockfill dams (CFRDs) have been modelled and constructed in the world, and many of these dams are located on the strong earthquake zones. Examination of the seismic behaviour of a CFR dam built on the seismic zone is very important to assess the safety and future of the dam. For this reason, the nonlinear earthquake behaviour of these dams should be constantly observed taking into account the seismicity of the zone. In this study, three-dimensional (3D) seismic behaviour of the Ilısu dam built on the East Anatolian Fault (EAF) line is examined considering the effect of the important various far-fault earthquakes. The 3D finite difference model of the Ilısu dam is created using the FLAC3D software based on the finite difference method. The dam body, foundation, and concrete slab constantly interact during the lifetime of the CFRDs. Therefore, the special interface elements are defined between the dam body, concrete slab, and foundation to represent the interaction condition. The Mohr–Coulomb nonlinear material model is used for the rockfill materials and foundation. Moreover, the concrete slab is modelled considering the Drucker–Prager nonlinear material model to represent the nonlinearity of the concrete. Very special seismic boundary conditions rarely used for CFR dams in the past are used in this work. These boundary conditions are free-field and quiet boundary conditions. The free-field boundary condition that is a very important boundary condition for the nonlinear seismic analyses is considered for the lateral boundaries of the 3D model. In addition, the quiet artificial boundary condition is used for the bottom of the foundation. While defining these boundary conditions, the special fish functions are created and defined to the software. Moreover, the hysteric damping coefficients are separately calculated for all of the materials. These special damping values are defined to the FLAC3D software using the special fish functions to capture the effects of the variation of the modulus and damping ratio with the dynamic shear-strain magnitude. In the numerical analyses, a total of 7 various strong far-fault earthquakes are used for the 3D nonlinear earthquake analyses, and 7 different numerical analyses are performed for the full-reservoir condition of the Ilısu CFR dam. According to the seismic results, the principal stresses for the three critical nodal points on the dam body surface are examined and evaluated in detail. It is clearly understood that the nonlinear seismic behaviour of the Ilısu dam changes depending on the magnitudes and periods of the far-fault earthquakes. Each far-fault earthquake has different seismic effects on the nonlinear principal stress behaviour of the Ilısu CFR dam.

Hydrodynamic Performance and Cavitation Analysis in Bottom Outlets of Dam Using CFD Modelling

“…On the other hand, to ensure the channel's proper operation, its associated hydraulic and hydromechanical installations, including gates and valves, the flow discharge capacity should be carefully examined along with performing hydraulic model tests [2]. By studying failure causes of dams' terminal gates, it has been determined that the cavitation phenomenon and gate vibration are the chief reasons for damages, because, in the areas where air bubbles collapse, pressure fluctuations intensity raises [3][4][5][6][7][8]. At the bottom outlets, the two-phase air-water flow is transmitted at high speed.…”

Experimental Centrifuge Study of the Effects of Valley Topography on the Behavior of a Concrete Face Rockfill Dam

“…Wang et al [17] studied the influence of valley topography on the deformation and stress of a high concrete face rockfill dam and found that the stress and deformation gradient of the face slab increased exponentially when the valley widthheight ratio was less than 2. Karalar and Çavus ¸li [18,19] used a WIPP-creep viscoplastic material model and a burgercreep viscoplastic material model to represent the concrete slab, rockfill materials, and foundation of a concrete face rockfill dam within an investigation of the deformation of the Ilısu Dam in Turkey. Gao et al [20] examined monitoring data for 22 concrete face rockfill dams across eight countries and found a low correlation between valley factors and deformation of the face slab below a certain valley factor threshold, whereas abrupt changes to the slope angle aggravated deformation of the slab.…”

Long‐Term Settlement of High Concrete‐Face Rockfill Dam by Field Monitoring and Numerical Simulation

“…Finite Element Method (FEM) has demonstrated advantages for predicting the mechanical performance of dams for better management and maintenance [20][21][22][23][24][25][26][27]. e FEM can also provide useful guidance for the design and construction of new high CFRDs by optimizing dam body structures, construction procedures, and dam construction materials [8].…”