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Probabilistic finite element analysis of failures in concrete dams with large asperities in the rock-concrete interface

Ulfberg Adrian, Gonzalez-Libreros Jaime, Das Oisik, Bista Dipen, Westberg Wilde Marie, Johansson Fredrik, Sas Gabriel

Archives of Civil and Mechanical Engineering

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2023

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Vol. 23, no. 2

art. no. e109, 2023

EN

Common analytical assessment methods for concrete dams are unlikely to predict material fracture in the dam body because of the assumption of rigid body behavior and uniform- or linear stress distribution along a predetermined failure surface. Hence, probabilistic non-linear finite element analysis, calibrated from scale model tests, was implemented in this study to investigate the impact of concrete material parameters (modulus of elasticity, tensile strength, compressive strength, fracture energy) on the ultimate capacity of scaled model dams. The investigated dam section has two types of large asperities, located near the downstream and/or upstream end of the rock-concrete interface. These large-scale asperities significantly increased the interface roughness. Post-processing of the numerical simulations showed interlocking between the buttress and the downstream asperity leading to fracture of the buttress with the capacity being determined mainly by the tensile strength of the buttress material. The capacity of a model with an asperity near the upstream side, with lower inclination, was less dependent on the material parameters of the buttress as failure occurred by sliding along the interface, even with inferior material parameters. Results of this study show that material parameters of the concrete in a dam body can govern the load capacity of the dam granted that significant geometrical variations in the rock-concrete interface exists. The material parameters of the dam body and their impact on the capacity with respect to the failure mechanism that developed for some of the studied models are not commonly considered to be decisive for the load capacity. Also, no analytical assessment method for this type of failure exists. This implies that common assessment methods may misjudge the capacity and important parameters for certain failure types that may develop in dams.

2

Failure simulation of Babar dam – Algeria and its impact on the valley downstream section

Gaagai Aissam, Boudoukha Abderrahmane, Benaabidate Lahcen

Journal of Water and Land Development

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2020

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no. 44

75--89

EN

A failure analysis of Babar dam on the El Arab River was performed to highlight the impact of flood wave and velocities on the four villages downstream of the dam; Hella, Khérenne, Chebla and El Oueldja. The simulation of wave propagation along the El Arab River under several scenarios was performed by the hydraulic HEC-RAS model. This model is dedicated to the description of floods at the dam following a breach in the dike. The main factors considered in this simulation include the level of flood water, the flood hydrograph, and the typical scenario for this breach. The flood risk analysis revealed that the maximum of flood wave flow registered at the breach is (Qmax = 9253.02 m3∙s–1), and is beginning to mitigate downstream of the dam along the El Arab River where it reached at the last village with a low flow (Q = 1110.64 m3∙s–1). This simulation allowed drawing the risk map which showed the areas threatened by flood wave resulting from a total failure of the work, and consequently required a plan of security measures to moderate as much as possible the consequences of floods. A sensitivity analysis was conducted to approach the parameters of impact of the breach on the dam failure scenario. It was confirmed that these parameters as formulation time, breach width and side slope have a great influence on the dam failure scenario with the four adjustments (±20 and ±50).

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Application of fuzzy cognitive mapping in the analysis of small earth dam failure

Shongwe Mduduzi I., Maseko Thabo, Vilane Bruce R. T.

Journal of Water and Land Development

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2020

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no. 44

136--142

EN

Small earth dams are most valuable in arid and semi-arid areas where they are used for both domestic and agricultural purposes. These dams however, continue to fail. The causes of such failures are interconnected in the sense that one can trigger the other. Most research into earth dams nevertheless, uses reductionist approaches. Such approaches do not consider the complex interactions between these modes and/or causes. This research used fuzzy cognitive mapping to identify the prominent modes and causes of small earth dam failure in Swaziland and to capture their interactions. A sample of seven earth dam construction experts was purposively selected from five institutions for individual interviews. An individual map was developed from each interview. An aggregated map was thereafter developed by combining seven individual maps. The results indicated that overtopping, piping and sliding were the common modes of earth dam failure. Overtopping was mainly due to siltation whilst animal barrows and tree roots were largely responsible for piping. Sliding was mostly associated construction defects and sudden drawdown. It was concluded that most of the failures were linked to poor management of catchments and that of the dams. It is recommended that future designs and management should increase the level of community participation in order to limit some of the causes associated with land use practices.