# Cracks in Arch Dams: An Overview of Documented Instances
## 1 Introduction
### Effect of Cracking on Arch Dams  
Among the different types of dams, arch dams have emerged as the most cost-effective and safest type of dam over the past few hundred years [5]. Arch dams are continuous monolithic designs in which the structural capacity is conditioned by the conduction of the received loads to its foundation in an undivided bonded system. Any interruption in the continuity or monolithicity of the structure or a weakening of the bedrock causes the dam to adopt a behavior for which it was not intended and can lead to dam failure or even total collapse if the foundation is affected. Globally, arch dams are susceptible to failure as a result of the following [6]:  
* Structural failure within the dam body;
* Sliding along the dam-foundation interface;
* Movement of the abutment rock wedges formed by rock discontinuities.  
These types of failures normally cause a high tensile stress in a certain area, leading to the formation of cracks. This cracking can be in the form of small surface cracks to severe crack damage. Minor cracks developed as concrete cures should not pose a risk to the reliability, appearance or maintenance of the dam. However, open cracks and cracks that connect different sections of the dam or penetrate deep into the structure can be harmful and should be the subject of attention.  
The maximum limit of the load-carrying capacity of an arch dam is determined by the compressive strength of the concrete, unless the dam malfunctions. The presence of cracks will reduce strength and rigidity, impair integrity and impermeability, aggravate concrete deterioration and jeopardize the safe performance of the dam. On this basis, joint opening and excessive and widespread cracking can deplete the concrete's ability to withstand compression as a result of load redistributions or may result in partial sliding. Causes of arch dam cracking often interact with each other in a non-linear way, so it is usually not possible to consider them separately, yet they can be summarized in the following categories:  
* Thermal effects: external temperature variations, freeze-thaw effects, hydration heat during concrete curing, etc. Due to its size and massive cross-section, significant thermal or moisture gradients may occur where parts of the structure are subjected to water, while other parts are in contact with the ambient air. These effects can introduce significant stresses into the structure. Most horizontal cracks in the arch dam are due to summer temperatures when the dam is empty and develop downstream. These cracks, although still required to be studied, are generally not hazardous because they will close once the reservoir is filled. More detailed information can be found in [7; 8];
* Chemical effects: expansive chemical reactions, shrinkage, alkali-aggregate reactions (alkali-silica reaction, alkali-carbonate reaction and sulfate attack), etc. More detailed information on chemical reactions in dams can be found in [9];
* External events: these include microseismic, earthquakes, deformation of the foundation, seepage, overtopping flooding, etc.;
* Inadequate design or execution of construction and maintenance: the profile of the arch dam is directly related to the stress distribution in the body of the dam, which can be affected by weak foundations, weak joints, not suitable concrete materials (high-strength concrete has high hydration heat), wrong design affecting its rigidity, gallery weaknesses, etc.