The project focuses on the theoretical and applied study of freezing soils in the context of the use of Artificial Ground Freezing (AGF) in excavations and underground construction. The ever-increasing density of urban environments poses new challenges to tunnelling for transit projects. This implies the necessity to carry out open excavations and bored tunnels in the urban environment, often in difficult ground and almost always in the close vicinity of existing buildings and structures. As a test case, the project examines the geotechnical aspects of excavation of Line 1 of Napoli Underground. The work was performed in the urban environment of one of the most densely populated cities in Europe. Monitoring included an extensive set of in-situ data (e.g. buildings displacements, temperature in the ground).The main objectives of the project are: a deeper understanding of the AGF process and of the effects of thawing frozen ground; development of a novel constitutive model and coupled thermo-hydro-mechanical (THM) formulation to provide an accurate description of the engineering behaviour of frozen/unfrozen soils; comparison between laboratory and field tests to calibrate the thermal properties of the ground, collection and back analysis of an extensive set of in-situ monitored data from a real urban tunnelling project. The most innovative aspect of the project is the way in which theoretical developments, constitutive modelling, laboratory tests, in situ monitoring and coupled analysis will be integrated in a single consistent framework firmly grounded on basic physical principles. The generality of the formulation and of the developed analysis tool allows the enhancement of the field of applications from AGF to the wider range of engineering and environmental problems involving frozen soils such as the analysis of frost heave, the study of the effect of freezing-thawing cycles in cold regions or the prediction of the permafrost fate in a climate change scenario.