Shotcrete excavations for the Munich subway - Comparison of different methods of face support in settlement sensitive areas

For the construction of shallow tunnels in settlement-sensitive urban areas it is very important to reduce the settlements and to increase the stability of the tunnel face during the excavation. In the case of shotcrete excavation, the use of different methods of face support has become more and more common. These methods are: ground freezing, pipe roofs, jet grouting and injection support. The paper shows the experience made to due the installation of the above mentioned face supports, especially since the specific focus is related to the arising settlements. If only small deformations are allowed to occur, as the examples show, deformations that have to be considered during the construction process as well as those to establish the bearing load; they could be significant depending on the process. Suggestions have been made as to ways in which the deformations can be reduced by making additional measurements.