# Cracks in Arch Dams: An Overview of Documented Instances
## 3 Results and Discussion: Comparative Analyses of Cracking
### Location of the Cracks  
Figures 3 and 4 present a compilation of diagrams found in the corresponding literature showing the location of the most important cracks. It should be noted that the location of cracks in multiple arch dams is mainly influenced by its own design. Being a non-symmetrical design, the loads will be distributed quite unevenly in each part of the dam.  
Figure 5 shows, on a generic arch dam, the areas where cracks were found for each of the dams studied. In addition, the type of dam corresponding to each one of them is indicated by a color code. It can be seen in this figure that a simple pattern cannot be found. However, some general trends can be observed:  
* Cracking happens more often in the downstream face than in the upstream face, and internal cracks are not unusual;
* Internal cracks can be found all along the height of the dam section;
* There is no specific area wherein the cracking concentrates on the downstream face, although it is more common in the abutment zones;
* However, cracking occurs more often at the toe and central areas and rarely in the abutments and crest area in the upstream face;
* Double-curvature dams tend to crack upstream in the crest zone and heel, while downstream on the sides and near the toe;
* Single-curvature thin dams do not usually have internal cracks or external cracks near the base of the dam. Cracking is mainly on the abutments, central and crest zones of the downstream face. When cracking occurs upstream, the cracks are located on the abutments;
* Gravity-arch dams tend to crack in the central zone of the dam upstream and in the central or crest zone of the downstream face.  
Regarding the cause of the cracking, it can be observed (Figure 6) that cracks due to chemical reactions generally occur on the downstream face or inside the dam body. Internal cracks are more often in the central part of the dam body than near the base or the crest, while cracks at the downstream face are evenly distributed among the different areas. No cases were found in which cracks were located in the abutments or crest area of the upstream face.  
Cracks due to inadequate design or execution of the construction and maintenance (Figure 7) are uniformly distributed throughout the different areas of the downstream face. It can be observed that internal cracks and those located on the upstream face are predominantly near the base of the dam. Considering the whole set of cracks with this type of origin, the location near the base is still predominant.  
Figure 2: Radial displacements of Kariba dam at the crest of the crown cantilever. Reprinted from [68].  
Figure 3: Part 1 of crack location diagrams. Main cracks highlighted in red. Images reprinted from cited references. * Downstream face. ** Upstream face. [11; 21; 30; 36; 38; 55; 69; 70; 75; 82; 83].  
Figure 4: Part 2 of crack location diagrams. Main cracks highlighted in red. Images reprinted from cited references. * Downstream face. ** Upstream face. [21,69,84,86,87,91,95,96,99].  
Figure 8 shows that most of the internal cracks and cracks located on the upstream face are due to the thermal effect, and also that most of the cracks are located near the dam toe on the downstream face. There are only a few cases in which cracks are located on the downstream face, far from the dam toe. It should be noted that cracks caused by thermal effect are predominant in arch dams as a whole.  
There are not many cases of cracked dams due to external events, and they are not concentrated in any particular location of the dam faces or body (Figure 9).  
Figure 5: Areas where cracks were found. Dotted lines divide toe, center, abutment and crest areas.  
Figure 6: Areas where cracks were found. Bold: cracks due to chemical effects.