Freezing process in porous media

Frozen soil is a multi-phases system composed of mineral particles, ice, unfrozen water and gas. Due to the existence of ice, several factors a ect frozen soil properties (e.g., pressure, temperature, salinity, etc..). Mechanical and deformation behaviour of frozen soil is not completely clear. A better understanding of physical frozen soil properties and of its freezing process are needed to improve the prediction of frozen soil deformation characteristics. This has application in aged cold region engineering problems such as the Frost heave but also in new issues of the modern era related to the Artificial Ground technique and to Global warming, since the recorded increasing creep settlements. This thesis describes di erent freezing procedures to make a elementary representative frozen specimen. Its mechanical response corresponds to the mechanical behaviour of soil only if the frozen specimen is homogeneous and isotropic and does not contain ice segregation inside the soil matrix. If not, the mechanical response would be the sum of that from ice and from frozen soil. Two kind of frost susceptible soil were investigated: Halden silt and Onsoy clay. The Onsoy clay showed ice lensing phenomena, while Halden silt frozen without the development of ice lenses. The analysis were computed on 3D images taken by the x-ray tomography scanner. Further investigation were carrier out on the 1D freezing process. Its evolution was scanned over the time by x-ray tomography. Moreover, this last allowed to explore and analyze phenomena involved by freezing, such us frost heave and section shrinkage for the clay. The frost heave and the maximum frozen height were measured for the 1D frozen clay specimen at di erent thermal gradients. A reliable quantification of section shrinkage was obtained by digital image processing of 3D images, taken during a one freeze-thaw-freeze cycle.