Overview
Surprisingly, the thawing of frost susceptible soils containing ice lenses has been only rare fundamental studies as he is the cause of damage to the most important buildings. The decrease in shear-induced melting of the lens is a phenomenon facture, and therefore expensive, affecting both infrastructure of roads and railways that the dangerous melting of mountain permafrost by global warming.
The research will try to explain, thermally, hydraulic machinery, how thoroughly ice lenses and how water from their melting is on the strength of the soil. It mainly uses for this:
- Tests to frost and thaw made in a large tri-axial cell (Ø 100 mm approx.) With temperature measurement in the unfrozen water content and capillary suctions cell developed for this research;
- Numerical simulations with a coupled models or (hydro-thermal coupling in particular).
This research follows the international trend of replacement of current empirical design methods of road or railway superstructures by rational methods based on mechanical laws of the continuum.
The results of this modeling should contribute to better understanding this phenomenon in practice and thus adapt our construction methods (standards for road construction for example) or prevention (melting of mountain permafrost) to this improved knowledge the phenomenon of melting of frozen ground.
Following steps will be provided during the project:
- The correct explanation of the physical phenomenon of thaw-thermally, hydraulics and mechanics.
- The application of the full phenomenon of melting ice lenses to real cases: infra-structures of roads or railways, initiation of debris flows during the melting of mountain permafrost.
- The results of this modelling should contribute to better understanding this phenomenon in practice and thus to adapt our construction methods (standards of road construction, for example) or prevention (melting of mountain permafrost) to the best knowledge of the phenomenon the melting of frozen ground.
Funding
Results
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 determined rather well by numerous experimen