**7. Conclusions**

extent along the dam axis was estimated between 150 and 200 m [45]. Consequently, water seepage was considered as an extra problem in the right abutment. Lugeon tests in this zone indicated values more than 60 due to the extent of fracturing. The prevailing hydromechanical behavior of the rocks at this abutment was dilatation and washout based on geotechnical

**Figure 20.** An upstream view of the displaced rock mass (DRM) on the right abutment [42].

The second problem expected for the Gotvand dam site, is leakage through its foundation via Agha-Jari layers [46]. These layers contain veins of gypsum usually associated with claystone beds. They appear as thin films on the beddings and along joint surfaces with a maximum thickness of 2 cm. The action of Lahbari and Pir-Ahmad thrust faults in the

investigations [44, 45].

90 Dam Engineering

**Figure 21.** Simplified geological cross section along the dam axis [44].

The knowledge of geological structures gives a reasonable in-sight in to dam construction studies. Site geology and availability of various geologic data obtained from site investigation is a key point in dam construction. It is also clear that the geological nature of different sites is not the same and depends on local and regional geology. Existing experience in dam construction projects shows that geological structure plays an important role in dam site geology and imposes major limitations on dam behavior during and after construction stages. In Karun-1 dam, for example, seepage through two springs downstream the right abutment are related most probably to existing shear zone at that abutment. Besides, rock falling and sliding on the dam abutments due to the downslope dip of bedding is another structure-related problem at the dam site. In Karun-3 dam, almost similar problems are observed but here, the presence of two sub-parallel thrust faults with opposite dip direction resulted in high stresses in the rock that intensified fracturing and subsequent permeability. Variability and complexity of geological structures regarding their tectonic situation result in different scenarios regarding dam's behavior. In this regard, the intersection of longitudinal and transverse faults in the vicinity of Marun dam caused the development of well and highly densed joint systems in the dam abutments that facilitated karstification. This in turn increased permeability of the rocks that was followed by extensive seepage during the dam construction. The role of geologic structure on geotechnical properties of dam sites is clearly seen in cases such as Gotvand Dam. Here, high fracturing and instability in the right abutment caused costly treatments including various stabilizing works such as grouting, geomembrane, and shotcrete. Finally, all the abovementioned examples indicate the impact of geological structure on various procedures either during constructing a dam or after its completion and close relation between structural geology and rock behavior.
