Tunneling in soil under the groundwater-level requires the sure removal of groundwater under construction. Different methods are available and they have proved in practice. There is to differentiate between the sealing, lowering and the squeezing of groundwater. While the sealing and the lowering of the groundwater have to anticipate the tunneling , it is necessary to squeeze the groundwater under construction. Standard solutions for groundwater-squeezing are the application for the support of the heading face by fluid or air pressure.

In this paper the main principles of tunneling under compressed air will be described. Based on the calculation methods for air flow, air requirement and air pressure the experiences of the last twenty years are summarized. In this connection it will be shown that always an air flow is necessary and has to hold up. Finally important recommendations are developed, risks will be described, the handling instructions with compressed air under construction will be defined and the application limits are referred.