**4. Karun-3 dam**

Karun-3 is a 205 m high concrete dam constructed at 28 km to the south of Izeh City (**Figures 1** and **8**) in the southwestern Khuzestan Province. Electric power generation and flood control were the main objectives of the dam construction. Karun-3 power plant has a capacity of 2000 MW, with an average generation of 4137 GWh/y. This is a double curvature concrete arch dam, with a subsurface powerhouse located downstream the dam and power tunnels [32, 33]. It has symmetrical shape regarding the shape of its valley. The location and alignment of the dam are limited by geological and topographical features on both abutments (**Figure 8**). The dam reservoir is 60 km

**Figure 8.** Upstream view of Karun-3 dam site before (left) and after (right) construction.

long with storage volume of 3 × 109 m3 . The dam was impounded in November 2004. The presence of a hazardous slope named G2M above takeoff yard and a big downstream spring named as Abol-Ghasem Spring is of the main concern here.

The dam body was constructed on Asmari formation on the southwest limb of Keyf Malek Anticline that is surrounded by elevated anticlines including Lapeh (in the northeast) and Monghast (on the southwest) [32, 34]. The reservoir area is underlain by Pabdeh, Asmari, Gachsaran, and Agha-Jari formations. The Asmari formation limestone is the main waterbearing formation at the dam site and reservoir area with a potential for karst development similar to that discussed previously (part1) and is reported for other dam sites in the Zagros Fold Belt and in this chapter (Karun-1 and Marun dams). The Keyf Malek anticline, on which the dam lies, is mainly consisted of lower Asmari outcrops (**Figure 9**).

It is made up of interbedded limestone and marly limestone with porosity values between 1 and 15.7% that imply medium to extremely porous rocks. The limestone is generally light gray to light brownish gray, fine to medium grained, strong to very strong [32]. The bedding strikes NW-SE with low dip at the anticline crest. On the southwestern limb, the dip of layers is very steep up to 80° due SW (**Figure 10**). The northeastern limb of the anticline has a dip of about 70°–80°. The fold axis shows a slight plunge toward the southeast (141°/06°). Regular joint sets are developed and these have consistent orientations across the project area. A major NW-SE trending fault named as Doshab Lori Fault passes within 500 m to the southwest of the dam site. Another major thrust fault cuts the northeastern limb of the anticline creating an overturned syncline between the Keyf Malek and Lapeh anticlines (**Figures 9** and **10**). The major seismically active faults in the study area [35] are presented in **Figure 11**. Some small faults cut the anticline parallel and normal to its axial trend.

Here, due to the downstream dip of bedding, which is unfavorable for a dam site, a natural potential for rock fall and slide on the dam abutments was predictable (**Figure 7**). This geological condition is of key importance since the southwestern (downstream side) limbs of the Zagros anticlines are usually very steeper than the northeastern limb due to the action of thrust faulting that affect the southwestern anticlinal limbs [30, 31]. New observations proved the subject and some rock slide and fall happened especially on the right abutment. There seems to be some flexuring along the bedding plane as well. The vertical tensional joints on

Karun-3 is a 205 m high concrete dam constructed at 28 km to the south of Izeh City (**Figures 1** and **8**) in the southwestern Khuzestan Province. Electric power generation and flood control were the main objectives of the dam construction. Karun-3 power plant has a capacity of 2000 MW, with an average generation of 4137 GWh/y. This is a double curvature concrete arch dam, with a subsurface powerhouse located downstream the dam and power tunnels [32, 33]. It has symmetrical shape regarding the shape of its valley. The location and alignment of the dam are limited by geological and topographical features on both abutments (**Figure 8**). The dam reservoir is 60 km

**Figure 8.** Upstream view of Karun-3 dam site before (left) and after (right) construction.

the right abutment could amplify rock falling.

**Figure 7.** Rock sliding (in yellow) at right abutment of the dam.

**4. Karun-3 dam**

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**Figure 9.** Geological map of the dam site area. Red star is the location of Abol-Ghasem Spring [36].

**Figure 10.** Geological section of Keyf Malek anticline [34].

**Figure 11.** Regional faults and distribution of earthquake epicenters around Karun-3 dam [35].

The strike and dip of the strata vary only slightly over the dam and powerhouse sites. The bedding has a fairly flat inclination at the top of the fold, but become rapidly steeper to the west of the axis, where it generally dips 60°–85° southwest (**Figure 12**). Mapping indicates that several strongly developed joint sets characterize the bedrock in the area.

As was mentioned above, instability of G2M above takeoff yard and leakage through downstream springs in particular Abol-Ghasem Spring are the main subjects of dam behavior in Karun-3 project. The rock slope, called G2M, is placed at the top of access road to the spillway on the right bank of the dam (**Figure 13**). The slope that is composed of limestone, marly limestone and marls besides developed tensional cracks created a potentially sliding mass.

**Figure 13.** Geological section (left) and downstream view of G2M (right) rock mass.

**Figure 12.** Downstream view of Keyf Malek anticline (left) and longitudinal fault cutting its southwestern limb (right).

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Generally speaking, the slope was probably formed by displacement and collapse of the layers consequently, pushing front layers toward the river valley [33, 37]. Alternation of the competent (limestone) with incompetent (marl and marly limestone) layers at G2M slope, besides the presence of thrust faults on both flanks of Keyf Malek anticline is most probably the main reason for instability of the G2M. It is very probable that a hidden blind fault cuts the core of the anticline regarding very sudden change in dip of the bedding on the southwestern limb of Influence of Geological Structure on Dam Behavior and Case Studies http://dx.doi.org/10.5772/intechopen.78742 83

**Figure 12.** Downstream view of Keyf Malek anticline (left) and longitudinal fault cutting its southwestern limb (right).

**Figure 13.** Geological section (left) and downstream view of G2M (right) rock mass.

The strike and dip of the strata vary only slightly over the dam and powerhouse sites. The bedding has a fairly flat inclination at the top of the fold, but become rapidly steeper to the west of the axis, where it generally dips 60°–85° southwest (**Figure 12**). Mapping indicates

that several strongly developed joint sets characterize the bedrock in the area.

**Figure 11.** Regional faults and distribution of earthquake epicenters around Karun-3 dam [35].

**Figure 10.** Geological section of Keyf Malek anticline [34].

82 Dam Engineering

As was mentioned above, instability of G2M above takeoff yard and leakage through downstream springs in particular Abol-Ghasem Spring are the main subjects of dam behavior in Karun-3 project. The rock slope, called G2M, is placed at the top of access road to the spillway on the right bank of the dam (**Figure 13**). The slope that is composed of limestone, marly limestone and marls besides developed tensional cracks created a potentially sliding mass.

Generally speaking, the slope was probably formed by displacement and collapse of the layers consequently, pushing front layers toward the river valley [33, 37]. Alternation of the competent (limestone) with incompetent (marl and marly limestone) layers at G2M slope, besides the presence of thrust faults on both flanks of Keyf Malek anticline is most probably the main reason for instability of the G2M. It is very probable that a hidden blind fault cuts the core of the anticline regarding very sudden change in dip of the bedding on the southwestern limb of Keyf Malek anticline. This structural feature is very common in the Zagros folds specially in highly deformed and stressed regions such as Izeh fault zone in which the dam is located [36]. High fracturing of the rocks at the dam site is also a sign of the governing role of fault activity in the study area. Successive occurrence of thrust faults cutting the region and overturning of the Lapeh Anticline northeastwards is an indication of extensive tectonic deformation of the region resulted in high and dense fracturing of the Keyf Malek anticline. Additionally, the apparent break in the bedding integrity in the southwest limb of the anticline might be a sign of longitudinal faulting along its strike (**Figure 12**). It should be noted that Doshab Lory fault that runs between the Keyf Malek anticline and Mongasht anticline is a back thrust with a movement in the direction opposite to the general direction of regional tectonic transport. Since, such structures are generally an indication of fault propagation folds, intense fracturing between fore thrust and back thrust is reasonable, which is almost seen for the Karun-3 dam site. As mentioned before, Karun-3 dam site lies in the northern part of Izeh fault (shear) zone that is distinguished by a variety of thrust and dextral strike-slip faults [14] so that their interaction created a complex highly deformed and sheared geological region.

with alternation of shale, marlstone gypsum, and anhydrite [38, 39]. The beds strike parallel to the dam axis trending NW-SE and average dip of approximately 35° due NE (**Figure 15**). The rock is regularly well jointed. Although fairly homogenous, the rock shows anisotropic permeability due to karstification of limestone. The rock strata at the site comprise a series of karstic limestones interbedded with water sensitive marls, which dip toward the reservoir. The main geological structures of the region include folds and faults aligned parallel to the main folding axis of NW-SE trend. The reservoir basin is centered mostly along the southwest flank of a broad northwest trending syncline. This feature forms a broad structural basin, approximately 9 km wide and 14 km long. At the dam site, two major joint sets are seen, the first parallel to the bedding, and the second perpendicular to it. However, a special set of

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**Figure 15.** A general layout of Marun dam and appurtenant structures [39]. BF is Behbahan thrust fault.

**Figure 14.** Upstream view of Marun dam site before (left) and after (right) construction.

Another challenging subject in the dam region is the presence of Abol-Ghasem Spring downstream of the dam site. It is located at about 2.5 km downstream of the dam site, near the right bank of the Karun River (**Figure 9**). Its water was recharged by Lapeh anticline karstic aquifer, before impounding with varying seasonal discharge nearly between 0.5 and 1.5 m3 /s, and increased to about 2.5 m3 /s after reservoir impoundment. Additionally, another seasonal spring about 70 m downstream of the Abol-Ghasem Spring was changed to a permanent one after the dam impounding. It seems that the both limbs of Keyf Malek anticline are potential paths for seepage equally [34]. Karstification of the northeastern limb of the Keyf Malek anticline along with thrust faulting intensified the seepage at the spring. The presence of an overturned syncline between the two anticlines indicates intense tectonic compression in the region that could result in dense fracturing in the existing two anticlines. Transverse faults cut across the anticline that is evident through sharp and sudden change of Karun River course downstream the dam site might facilitate the occurrence of springs.
