Evaluation of structural safety reduction due to reservoir water penetration into a major structural crack in a large concrete dam

Structural damages in arch dams, are often of major concern and should inevitably be evaluated for probable rehabilitation to ensure safe regular normal operation and safe behavior in future under unusual loading. These are crucial to prevent any catastrophic or failure consequences for the life time of the dam. If there is a specific major infection such as a large crack in the dam body, the assessments will be necessary to determine the current level of safety and predict the resistance of the structure to various future loading, such as earthquakes, etc. In this research, Morrowpoint dam is selected as a case study to assess the dam performance and its safety level, at the presence of an actual crack with almost known geometry created in the dam body during the sequence of its reservoir first impounding. Three-dimensional modeling of the dam and its foundation is constructed for several different crack types with specific geometry and different mechanical properties. For modeling of both the existing cracks, and the vertical contraction joints of the arch dam, no-tension, zerothickness joint elements with variable compression-shear behavior are used. The applied loads include normal or service loads (weight and hydrostatic water pressure) as well as abnormal load of water penetration into the crack surface. In the first set of analyses, concrete material is assumed as linear. By observing the high tensile stresses, non-linear concrete materials with plastic damage model is introduced for selected cases although the foundation materials remain as linear. Safety factors of shear and compressive tractions are calculated at the surfaces of the contraction joints and the cracks. For the safety factor of the dam body mass concrete surfaces, a 2-D failure criterion is employed. In applying the weight load, the construction sequence of 3D blocks of the dam, and the stages of grouting the contraction joints have been fully accounted for. The results indicate that for cracking with an extension depth of half the thickness of the dam body, for both cases of penetration and non-penetration of water load into the cracks, safety factors are only slightly reduced and thus the dam safety in normal loading condition remains acceptable. However, in the case of increasing the depth of crack extension into the entire thickness of the dam body, the friction angle of the cracked surface is crucial, and if reduced, the normal loading safety factors of stresses and joints tractions are reduced significantly even when neglecting water penetration effects in cracks. When water penetration into the cracks is added during normal loading case, the situation is of much concern and great damages are expected. Simultaneously, it is observed that, the foundation interface also suffers of much shear safety loss.