Construction of the looped shunt tunnel collector at Obukhovskoy Oborony ave. comes to the final stage

04.07.2017

Laying of the looped tunnel collector going under the Neva from Obukhovskoy Oborony ave. to Zolnaya str. is completed. The facility shafts are now being technically equipped.

The construction of this facility will allow repairing of two existing collectors: the first along Glazurnaya and Zerkalnaya streets, the second along Glinyanaya and Melnicnaya streets. Today, they transport wastewater from Nevskiy and Frunzenskiy districts to the Northern WWTP (about 300 thousand cubic meters per day in average). The looped shunt tunnel will divert this wastewater to the Northern WWTP catchment area making it possible to take the existing collectors out of operation and repair them.

Technical inspections of the collector condition along Glazurnaya and Zerkalnaya streets and the collector along Glinyanaya and Melnicnaya streets showed their progressive deterioration: gas corrosion destroys the reinforced concrete jacket and the reinforcing mesh weakening the entire structure of the tunnels and major repair is required. Both facilities have been in operation for more than 50 years. The length of the first collector is 824 m, the second is 1272 m.

Looped and backup tunnel collectors allow performing repair of worn tunnel collectors without discharging untreated wastewater into the city water bodies. The combined sewerage tunnel under the Neva is under construction for this purpose as well. Implementation of such projects is an important part of the program to improve reliability of the sewage system.

The looped tunnel collector under construction includes a tunnel of 2.5 m in diameter and 615.4 m long, a starting shaft No. 1/27 (33 Obukhovskoy Oborony ave.) with the diameter of 9.8 m and a receiving shaft No. 441/2 of the Northern Tunnel Collector (at the intersection of Oktyabrskaya Embankment and Zolnaya Street) with the diameter of 8.5 m.

The tunnel is laid under the Neva at the great depth from 8 to 51 m. The depth fluctuations are due to the peculiarities of future tunnel connection to the existing shafts as well as the hydraulic slope of the collector. Driving of the tunnel collector was carried out using Herrenknecht microtunneling equipment method and construction of the shafts was implemented with the method for artificially frozen soils.

Construction of the looped shunt tunnel from Obukhovskoy Oborony ave.to Zolnaya street is planned to be fully completed in December 2018.

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It is to be recalled that that 98.5% of wastewater in St. Petersburg is treated today. Municipal wastewater is transported via the sewerage tunnel system to Vodokanal WWTPs to be treated in accordance with all Russian and international standards including the nutrient content recommendations of the Baltic Marine Environment Protection Commission.

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