A dam needs to be constructed to provide power for a developing area of the world.  These types of dam projects are expansive and produce a large reservoir of water. The diversion tunnels are the first job to construct the dam and structures that are designed to operate under high pressure. They include a steel plate of flow gates that can be raised or lowered to either prevent or allow water to be discharged from a reservoir, like the faucet in the sink controls the flow of water.  After the diversion tunnels are complete the outflow structure must be constructed.

Chang-soo Park had worked for Thumb-up Engineering & construction which is an international company in Korea. He was dispatched as the civil supervisor of Rockfill dam (Masfed-e-solei HEPP project) at Goar-f-lande,  Iran. (Hydraulic Turbine generator : 250MW X 4 units)  In the middle of September the subcontractor installed the water gate in diversion tunnel to change the waterway for using the other water gate.  In this site there are two diversion tunnels which were constructed for 3 years ago.  The water gate was installed on the concrete structure by 100-ton crane during 3 days.

Diversion tunnel Dimension
  Diameter : 12 meters
  Length     : Approximately 1 km
  Material   : Reinforced concrete structure

The design compressive strength of concrete was 25MPa and slump was 7~10cm and mixture proportion of concrete was determined as cement (Type I): 305kg/m³, water: 186kg/m³, sand: 869kg/m³, gravel:1,026kg/m³ and water-cement ratio 0.61.

Inspectors found the map cracks as well as linear cracks, abrasion and scaling phenomena in many places at the diversion tunnel.
The Q/C team checked this tunnel and reported the status of damage. There were a variety of physicochemical process, such as an attack by sulfate, wetting and drying cycles of freezing and thawing, and alkali-aggregate reactions, causing deterioration and distress of reinforced concrete structures and compressive strength was below the specification.  There was extensive brown staining coming from the cracks on the surface of the structure.

What is the problem with the dam?

What could be done to improve this and similar dams?

How can the dam be repaired?

Additional Information:
The climate of this site is severe for concrete structures. Risk of whether damage is high, as the number of freezing and thawing cycles comes to 50~70 per year according to weather data. All season strong winds blow from the sea and chloride ion content in the air is high.