Hofolding Gallery

The Hofolding Tunnel represents a part of a long-term programme to assure the quality of Munich's drinking water. The overall scheme consists of a 30 km long pipeline in the form of a hydrostatic pressure line and further operating facilities. The tunnel route is completely located in quaternary gravels of the so-called Munich "Schotterebene" above the groundwater table. These gravels are extremely heterogeneous and place severe challenges on the flexibility of the tunnelling method on account of their "blast-proof" conglomerate benches and non-cohesive rolling gravel layers. The roughly 17.47 km long Hofolding water tunnel was driven via a central starting shaft. With the exception of the ventilation, which is successively relocated, the entire supply and disposal needs for the drives take place via this shaft. First of all, the southeast artery (length: 9.43 km) was driven towards the "Grub" target shaft at a gradient of 1.55 ‰. Here it is linked up with the Mangfall Tunnel. Then the machine was reinstalled in the starting shaft in order to produce the northwest artery (length: 8.04 km) with a gradient of 2.34 %o towards the "Gießental" target shaft linking up with the Hachingen Tunnel. The tunnel is being driven by means of a variable shield machine, which on the one hand can be used as a cowl shield (selective cutting technology) and on the other as a full-face tunnelling machine with mechanical face supporting once the driving unit is changed. The excavated diameter for both modes of driving amounts to 3,400 mm; the cavity is secured by means of fibre-reinforced segments with a clear width of 2,900 mm and a wall thickness of 180 mm (6 segments, conicity 1 cm, length 1,000 ± 5 mm). The remaining annular gap is grouted with mortar. All materials are transported on tracks. The drive commenced using selective cutting technology. In this way, it was possible to identify the properties of the subsoil better so that the findings gained could be used for the final design of the full-face excavating machine. Providing the geological conditions allowed it, it was planned to replace the selective cutting head by the full-face mode. The envisaged machine was designed as a cowl shield with selective cutting geometry. The cowl angle can be adjusted by means of poling plates to fit varying soil conditions. A shovel or hydraulic chisel can be applied for extraction purposes or alternatively a rotating cutter head can be installed. The full-face tunnelling machine possesses a rotating cutting wheel, which has been fitted with a special flap system to support the face. It was essential during the design phase to consider that both blast-proof conglomerate as well as non-cohesive rolling gravel layers had to be tackled - both in mixed-face mode as well. When converting from a selective cutting to a full-face machine, it is only necessary to replace the front section of the machine; the central section with the main jacking station and erector, the tail skin and the back-up remain in the tunnel. After completion of the segmental lining, the tunnel can be finished via previously produced intermediate shafts. This entails driving steel pipes into the tunnel, which are then welded, so that the column of pipes is installed in its desired position. After the entire column is completed, the remaining annular gap is filled with insulating material. Subsequently, the tunnel inner shell is sealed with a cement mortar lining that is water neutral.

Country: Germany
Region: Bavaria
Tunnel utilization: Utilities
Type of utilization: Water SupplyTunnel
Client: City of Munich
Consulting Engineer: Bilfinger Berger AG, IMM Prof. Dr.-lng. B. Maidl-Dipl.-lng. R. MaidI
Contractor: Bilfinger BergerAG
Main construction method: Trenchless
Type of excavation: Shield machine (SM)
Lining: Reinforced concrete segments
No. of tubes: 1
Tunnel total length: 17,470 m
Cross-section: 9.08 m², diameter 3.40 m
Contract Volume: € 59.7 million
Construction start/end: 2002 to 2007
Opening: 2008