Publication
Curiously, the thawing of frozen soils containing ice lenses has only been the subject of rare fundamental studies even though it is the cause of the greatest damage to constructions. The reduction of bearing capacity caused by the thawing of the ice lenses is a destructive phenomenon, and thus costly, which concerns roadway and railway infrastructures, as well as the melting of mountain permafrost by global warming. The present research, especially experimental, has tried to explain how ice lenses melt and how the water produced by the melting acts on soil properties, in particular on their deformability. Numerous freezing and thawing tests have been carried out in a testing apparatus including : A mould containing a specimen 150 mm in diameter and 300 mm in height. It is slightly conical in order to reduce the friction against its walls due to swelling. Numerous gauges placed on the sides and in the specimen in order to measure temperature, unfrozen water content and suction. Three cryostats, which control temperature at the head of the specimen (positive and negative), at its base (always positive) and outside of the thermal insulation placed against the mould. A micro-camera (endoscope), which moves in a translucent tube placed along the axis of the specimen, which enables animations of the growth and melting of ice lenses to be made. A press to enable loading and unloading cycles to be applied to the specimen. An X ray device using lead shot placed in the specimen, which enables the measurement of deformation in the entire specimen during the freezing and thawing cycles. All of the tests were carried out on one very frost–susceptible silt. Their duration of approximately two months excluded the possibility of carrying out tests on several types of frost–susceptible soils. Some numerical simulations permitted the verification of the thermal behaviour of the test apparatus. Then, previous freezing and thawing tests carried out at full scale on road pavements, carried out in a large test pit, were reinterpreted in order to obtain improved information on the deformability (resilient moduli) of the frost–susceptible infrastructure which was made up of a silt similar to that tested in the laboratory tests described above. The results of the laboratory tests and the reinterpretation of the full–scale measurements on road pavements were used for two very different practical applications : the design of roadway and railway pavements by quantitative methods using, in particular, resilient moduli and the formation of mountain permafrost and its thawing due to global warming. In the general field of the physical phenomenon of freezing and thawing of frost–susceptible soils, the very elaborate experiments permitted the measurement, with precision and reliability, of numerous parameters which are involved in the phenomena of freezing and thawing of fine-grained soils. However, most of these phenomena were already known and their parameters have been deter
Charlotte Grossiord, Christoph Bachofen