Geomechanics and Geophysics at Duke University
Environmental Mechanics of Geomaterials
Failure in many engineering systems including geo-systems occurs at mechanically subcritical states, after both long- and short time exposure to adverse environmental conditions. These conditions include elevated temperature, due to embedded infrastructural elements, such as nuclear waste canisters, high voltage cables, mined hot fluids and gases or energy storage structures; ground water causing dissolution of minerals, changes in the former due to ionic concentration, strength, electric charge, acidity evolution; both evaporation and condensation of pore fluid, to mention the few. Often such environmental variations are the effective cause of the mechanical failure of the aforementioned system. Effort is needed to improve our current poor understanding of both the critical variables, as well as the actual mechanisms, through which such variables are coupled to the mechanical soil material properties and variables, as well as inadequacy of computational methods that seriously impede our capability to assess the performance and predict service time of the affected geo-structures.
We are developing in parallel both experimental data base and theoretical models that would allow us to identify the mechanisms of coupling between the mechanical properties of soils and chemical, thermal and physic-chemical variables characterizing the (fluid and gas) soil environment, both external and internal. For instance, we have developed a method to experimentally capture and study gas entry mechanism into drying capillary grain system developing within 1/200th of second. On the theoretical side, we have developed models of microchemo-plasticity to deal with the effect of mineral dissolution on material damage of a grain.
One of our key findings in the area of pore space evolution during drying is that the change in the major pore size controls the material desiccation shrinkage in the stage of material saturation, and the corresponding suction defines the air entry event, via a criterion of water body failure near the soil body boundary. The subsequent partial saturation stage the major pores empty quickly and the minor pore size controls the suction, and imposes much smaller shrinkage rates.
Developments in the understanding of environmental impact on materials form a base for quantitative prediction of long-term performance and durability of materials, including geomaterials and civil engineering structures and infrastructure. They allow us to explicitly include rates of chemical and geochemical reactions, physico-chemical and transport processes into the models of mechanical processes of damage and irreversible deformation. They allow for a better assessment of degradation of geomaterials.
1. Hueckel T., B. Francois, L. Laloui, 2011, Temperature dependent internal friction of clay in a heat source problem, Geotechnique, 61, in print (available on line).
2. Hueckel T., 2009, Thermally and Chemically Induced Failure in Geomaterials, European J. of Civil and Environmental Engineering, v. 13/7-8, pp. 831-867.
3. H. Peron, L.B. Hu, T. Hueckel, L. Laloui, 2009, Desiccation cracking of soils, European J. of Civil and Environmental Engineering, v. 13/7-8, 869-888.
4. Hueckel T., B. Francois, L. Laloui, 2009, Explaining thermal failure in saturated clays, Geotechnique, 59, 3, 197-212.
5. H. Peron, T. Hueckel, L. Laloui, L.B. Hu, 2009, Fundamentals of desiccation cracking of fine-grained soils: experimental characterisation and mechanisms identification, Canadian Geotechnical J., 46, 1177-1201.
6. L.B. Hu and T. Hueckel, 2007, Coupled Chemo-mechanics of Intergranular Contact, Special Issue on “Chemo-mechanical Interaction in Geomaterials”, Computers and Geotechnics, vol. 34, 4, 306-327.
7. L.B. Hu and T. Hueckel, 2007, Creep of saturated materials as a chemically enhanced rate-dependent damage process, Int. J. for Numerical and Analytical Methods in Geomechanics, 31, 14,1537 – 1566.