In the course of the planned underground extension of the central station in Bern, an access tunnel had to be constructed from an existing shaft. The first 60 m of this tunnel cross through unstable, water‐bearing and unconsolidated rock, and run under existing railway tracks. Thyssen Schachtbau GmbH has been commissioned the contract to carry out an artificial ground freezing measure to enhance the realization of the tunnel construction. The horizontal directional drilling work within the shaft as well as the construction and operation of the freezing plant were carried out in 2020 in a very confined space, and parallel to the ongoing operation of the train station. In order to ensure sufficient water saturation and thus the freezability of the unconsolidated rock, artificial ground irrigation procedure was operated. After completion of the predefined frost body, the tunnel was successfully and safely driven from the shaft into the bedrock.