Micro-tunnel under the Saimaa Canal
The tunnel under Saimaa Canal is a final stage of the grand project of the North-European gas pipe line construction at its section between Gryazovec and Vyborg. The key feature of the tunnel is defined by geological conditions. At the construction site rock formations, intermitting with hybrid water-bearing grounds, clays and loam soils, prevail.
Aspect, affecting the complexity of the construction, is route’s geometry. The canal width where the driving takes place is no more than 100m; however, the length of the tunnel doubles this size. The difference is caused by significant tunnel’s route inclination.
Original design of this section of the gas pipe line suggested construction with cut-and-cover method, with the part of the channel being drained and the pipe lays on its bottom. But during navigation time the canal is in use, so the project was declined. Besides, it required the closure of the road to one of the border posts between Russia and Finland, and was not safe for environment.
New project involves micro-tunnel-boring complex AVN-2000D, allowing implementing the project under different geological conditions (from rock formation with hardness over 300 MP to soft loam soils with boulders). The project was developed by institute “Lenhyproinzhproekt” and contemplates driving of the tunnel under Saimaa canal for both gas lines.
Moreover, ООО «Tonnelny otryad - 4» in the course of construction of the section Gryazovec - Vyborg of the North-European gas pipe line carried out two crossings under Neva river and several crossings under rails, where required.
Key features of the construction:
- Tunnel is a part of unified gas transmission network of Russia and joins the system with gas pipe line "Nord Stream".
- The length of the tunnel is 250m; maximum depth is 25m; diameter – 2m; maximum angle of inclination - 5 degrees.
- For implementation of the project ОАО «Metrostroy» purchased new cutting head for tunnel-boring machine AVN-2000D, allowing completing its construction in time and with a high level of quality, answering European level.
- This construction helped to preserve unique ecological environment of the Saimaa canal and avoid the closure of the road, crossing the tunnel route.
- Construction of the tunnels for other purposes with diameters of 1.5-2.5m with special equipment for micro-tunnels driving is in-demand when cut-and-cover method is inapplicable due to the absence of required space, for example, in densely built-up areas.