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Urban railway tunnel

The extension of the MUNICH urban railway system includes the construction of the Am Hart station by cut-and-cover techniques. In order to avoid the need for comprehensive dewatering measures the station is being constructed in a sealed cofferdam. This was constructed from 8700 m sq. of U-shaped paired sheet piles, Beltan-sealed, and measuring 18-20 m in length.
During excavation two layers of grouted anchors were installed and the groundwater was pumped out of the cofferdam. After completion no seepage was noted through the piling interlocks from the adjacent groundwater.

Whilst installing the sheet piling care had to be taken to ensure that the highly sensitive mainframe computers in the neighbouring BMW Research Centre, and the operation of a glass manufacturing company in the immediate vicinity were not affected. Consequently the client stipulated that vibration action be limited to 0.5 mm/s, which is considerably lower than the values stipulated in DIN 4150.

In addition, jetting lances were employed so as to reduce penetration resistance, by employing a combined vibration and flushing technique. In applying this technique, the sheet piles were driven using a PTC 46 HF1 high frequency vibrator fitted with a leader (maximum centrifugal force of 2600 kN at a vibration frequency of 40 Hz). This enabled the vibration limits indicated above to be met.

 Owner State Capital of Munich, Urban Railway Department
 Consultant Panenka & Labmair
 Contractors Arge Kronibus, Züblin, Nagelscheider and TGB TechnoGrundbau Gmbh
 Steet piles LARSSEN BU25, 163 kg/m2, 2 500 cm3/m
 Steel Grade St Sp S
 Mass 1 400 t