Tue, 2013-04-16 13:24 | 
PHD THESIS DESCRIPTION
In the last 20 years concrete faced rockfill dams (CFRDs) have been designed and built in increasing number in China, Brazil, USA, Australia, South-East Asia and in various parts of the world. In Greece, the tallest CFRD is Mesochora Dam (Thessaly), having a height of 150m (Dakoulas 2007). More than 150 CFRDs have been completed or are under construction in China, 14 of them having a height >150m (Ma & Cao 2007). The Shuibuya Dam (China), 233m height, is nowadays the tallest CFRD in the world, but not for long. To respond to the increasing need for water and clean energy production, extra-high CFRDs, having a height > 150 m, are necessary for further investigation.
CFRDs have material zones. A typical Dam cross-section is composed of the upstream zone 3B, the downstream zone 3C and a gravel zone 2B beneath the slab. The upstream slab consists of independent concrete panels, which at its base interface with the gravel layer.
CFRDs have some significant and important advantages (Sherard & Cooke 1987, Wieland & Brenner 2007, Ma & Cao 2007: (a) The high friction angles achieved with compacted rock and gravel fills and the absence of an impervious zone with high pore water pressures during rapid drawdown, enables designing the dam body with steeper slopes and reduced volume. (b) Stabilising effect of water load: The resultant of the water load is transmitted into the foundation upstream of the dam axis. (c) Compaction of the rockfill during rainfall is even advantageous as it reduces the need for wetting the material being placed. (d) Because of smaller fill volume, resulting from steeper slopes, a CFRD is usually more economic than the other types of dams. (e) They are less demanding on materials from distant regions. (f) They achieve faster construction, safer operation and easier maintenance.
In the last 30 years, there is a lot of experience about the behaviour of CFRDs. (Cooke 1984, Sherard & Cooke 1987, Gazetas & Dakoulas 1992, Marques Filho & Pinto 2000, Marulanda & Pinto 2000, Fell et al. 2005, Hunter & Fell 2003, Johannesson 2007, Ma & Cao 2007). This general experience shows that the behaviour of CFRDs depends mainly on: rockfill stiffness, canyon geometry, dam foundation stiffness, structural integrity, watertightness of the face slab panels, design of joint water stops for all types of joints such as joint between face slab and plinth or toe wall and vertical joint between strips of face slab, etc. The rockfill stiffness and the canyon geometry are of crucial importance in reference to the behaviour of CFRDs. Due to deformations in the rockfill the concrete face slab will experience cracking, allowing water leakage, which may further increase settlements. There are three types of concrete slab damage: (a) Structural tensile cracks in the face slab, causing significant seepage. Examples: Aguamilpa Dam (Mexico, Marques Filho & Pinto 2005), Tianshengqiao-1 Dam (China, Marques Filho & Pinto 2005, Ma & Cao 2007). (b) Compressive failure in a perimeter zone (parallel to plinth). Examples: Xingó, Itá and Itapebi Dam (Brazil, Marques Filho & Pinto 2005). (c) Compressive failure and spalling of the face slab along the vertical joints, because of the low rockfill stiffness, the hight of the dam and the narrow of the canyon. Example: Campos Novos Dam (Brazil, Ma & Cao 2007).
In the case of dams built in narrow canyons, a simulation of the phased construction of dams and subsequent reservoir impoundment, a realistic modeling of the 3D geometry of the slab panels, the nonlinear material behaviour and the contact conditions at the concrete base and the vertical joints between adjacent slab panels, are essential.
The objective of this PhD Thesis is to investigate numerically the behaviour of three concrete faced rockfill dams (CFRDs), taking into account the nonlinear material behaviour. Specifically, the followings are suggested: (a) An advanced elastoplastic model. (b) A numerical analysis, which is going to be conducted using the general purpose finite element code ABAQUS and a model's verification. (c) An investigation on the effect of rockfill stiffness and dam height of three CFRDs (H = 100m, 200m and 300 m). The dams are built in narrow canyons, having a trapezoidal shape with the same aspect ratio equal to L/H=2. (d) The effect of the rainforced concrete slab. (e) Detailed analysis of the behaviour of a real CFRD (Mesochora Dam and Karahnjukar Dam are two possibilities). (f) Conclusions for the design of extra-high CFRDs.
Ph.D Candidate:
Stavrotheodorou Eleni
Department:
Department of Civil Engineering
School:
School of Engineering
Supervisor:
Assoc. Professor Dakoulas Panos (dakoulas@uth.gr)
Supervising Committee:
(1) Dakoulas Panagiotis (2) Giannakopoulos Antonios (3) Papadimitriou Achilleas Παραδοτέα έργου δημοσίως προσβάσιμα:
