Evaluation of ground freezing data from the Naples subway

Abstract

The method of artificial ground freezing was employed to ensure stability and waterproofing of the platform and escalator tunnels in the Università station of the Naples underground. The paper presents the temperature histories monitored within the ground during the freezing process. Furthermore, the importance of the mineralogical composition of the ground is discussed and it is shown that the temperatures monitored can be interpreted numerically using the ‘Freeze' code, a thermo-hydraulic software developed at the ETH Zurich. The influence of important parameters, such as the spacing between the freeze pipes, the thermal conductivity of the ground and the time–development of cooling temperatures in the freeze pipes, is investigated and critically discussed in order to gain a better understanding of the thermal behaviour of the ground during artificial freezing with liquid nitrogen. ‘Freeze' software is a powerful tool for analysing field data for cases involving non-constant temperatures within freeze pipes.