District heating transmission line English Garden

When choosing the location line and the construction method of an approx. 6.5 km long district heating transmission line from the Northern border of the city to the inner ci ty through the English Garden because of reasons of landscape, nature and environmental protection and because of the special importance of the English Garden for the population only a method of tunnel construction without groundwater lowering or compressed air respectively was possible. The chosen location line crosses the Isar-works-channel at the shortest distance as well as the Isar itself and runs along the Western border of the English Garden to the Königin-Street. The shafts which were necessary for operation were made in a way that the greens of the English Garden were not damaged. The lengths between the shafts are 700-1200 m, the depth of the shafts up to 28 m. The tunnel driven by underground technique with a total length of approx. 6.0 km and 6 shafts was called for tenders separately in 4 lots.

lot 1 shield driving Ø 4.20 m, L = 2.160 m
lot 2 shield driving Ø 4.40 m, L = 2.208 m
lot 3 shield driving Ø 4.40 m, L = 1.112 m
lot 4 shotcrete tunnelling method Ø 5.10 m, L = 676 m

The construction period for the execution of the tunnel works was between 17 and 20 months. A special proposition was chosen which included mainly the following changes:

extension of the diameter in lot N 1 from 4.20 m to 4.40 m
tunnelling of lot N 2 in 2 sections from shaft "Am Biederstein" with the shield driving machine from lot N 1 and from shaft "Grasmeierstraße" with the shield driving machine from lot N 3.

Below the quaternary soil layers - namely bad sorted fine to coarse gravel partly with sandy and silty components - the tertiary layer follows, an irregular alternating sequence of sands, silts and clay marl. Quaternary rubble and tertiary sands are separated over long distances of the tunnel line by retaining mica marl one from another. Thus in the tertiary sands pressured groundwater horizons are existing which normally do not correspond with the quaternary groundwater horizon. In some sections there are, however, natural or artificial short cuts between the different groundwater horizons, so that the tertiary water horizons can level up to the pressure of the quaternary groundwater. For driving the tunnel line 2 shield driving machines with an external diameter of 5.20 m were used. Due to the geological and hydrological conditions the decision was made for a machine with a dry mucking system under compressed air. The shield had a cutting wheel which could be turned infinitely variable to all sides. The bore head was formed as horizontal conical frustum with bearings as well at the cutter as at the tapered end. The outcropped material fell after loosening through the openings between the arms of the bore head into the rotating chamber. There it was automatically lifted to the top and was discharged onto a conveyor belt which was situated in the middle. The shield body was divided into two parts by articulation and with jacks, situated in the articulation, course corrections could be made by turning the bore head. The bore head could be closed in some seconds by hydraulically movable segments. For lots N 1 till N 3 a one-shell, watertight reinforced concrete segmental lining d = 30 cm was foreseen. The conical, 1.20 m wide tubbing rings consisted of 5 normal segments and a keystone each. Still in the factory, the tubbings were equipped with a neoprene sealing frame for sealing the joints.

Country: Germany
Region: Bayern
Tunnel utilization: Utilities
Type of utilization: District heating transmission tunnel
Client: Stadtwerke Munich
Main construction method: Trenchless
Type of excavation: Shield machine (SM)/Drill-and-blast
Lining: Reinforced concrete segments/Shotcrete?
No. of tubes: 1?
Tunnel total length: 6100 m
Cross-section: 4.4 m internal diameter
Contract Volume: 86 Mio. DM
Construction start/end: 1989 till 1992
Opening: 1992