Abstract
The operation of a hydro power project in North Turkey started in 2015, included the 12km long headrace tunnel. An 8km long lower tunnel section was excavated by double shield TBM technology with 8.7m ID. Due to problems with the mechanised excavation, a 4km long upper tunnel section was excavated conventionally by the Drill and Blast method with single shell lining generated from fibre reinforced sprayed concrete and rock bolts. Significant operational problems were observed in September 2016. The flooded tunnel was investigated by underwater Remotely Operated Vehicle which indicated significant collapses. Operation of the power station had to be stopped and water from a supply dam at the headrace tunnel inlet had to be discharged to enable dewatering and inspection of the tunnel. Consequent investigation revealed three major collapses and a considerable variety of other damages in the D&B section of the tunnel. Repair and strengthening of the tunnel was completed in October 2017.
Highlights
The water tunnel is located in North Turkey in the area of the North Anatolian Fault between the Eurasian plate and the African plate (Figure 1)
The whole part excavated by shield was permanently supported by segmental lining with steel cages, the whole Drill and Blast (D&B) part was permanently supported by single-shell steel fibre reinforced sprayed concrete, CT bolts and a cast in situ concrete floor at the tunnel bottom
Very specific and rare problems had to be solved during the water tunnel repair and with a very significant time pressure
Summary
The water tunnel is located in North Turkey in the area of the North Anatolian Fault between the Eurasian plate and the African plate (Figure 1). The lower part of the tunnel is geologically very variable including sandstones, mudstones, conglomerates, ophiolitic and continental units, metalavas, marbles, etc. The upper part of the tunnel is situated in volcanic rocks (basalts and andesites with dykes). The maximum tunnel overburden is about 600 m, and the difference of water tables in upper dam and lower dam is about 80 m. A surge shaft is situated above the tunnel close to the power house
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