Example: Column on Slab - exposure to salt solution
The figure shows the distribution of the degree of hydration after 100 days. Inside the structure m achieves nearly the final value. In contrast this the drying effect of the ambiance stopped the hydration process in areas near to the surface. Between the slab and the column, the degree of hydration is smaller because of the successively concreting of slab and column.
Example: Pillar exposed to sulphate attack
For landfill monitoring and aftercare, long-term prognoses of emission and deformation behaviour are required. Landfills may be considered as heterogeneous structures, in which flow and transport processes of gases and liquids interact with local material degradation and mechanical deformation.
Coupled THMC processes are described by means of a complex continuum mechanical approach. Prognosis of long-term behaviour of landfill structures can be investigated seriously only by considering the coupling of the most important processes on the landfill-site as well as the different scales in space and time to be observed. Balance equations of momentum, mass and energy consider stress deformation behaviour, transport phenomena and biochemical reactions.
The concept of effective stresses is included in the mechanical equilibrium and thus a separate description of different settlement phenomena is enabled. The compaction model combines stress-dependency of compaction rate with density-dependence. The creep rate is coupled to degradation by the solid dry bulk density.
In porous media, the degradation of organic matter leads to time-dependent deformations and to changes in pore structure. Heat generation from exothermic reactions is considered, whereas the temperature has the determining influence on the degradation kinetics. The emerging landfill gas emanates via the pore space.
Example: Degradation induced settlements
Long term analysis of a landfill structure is performed to investigate the influence of varying temperatures on settlements and degradation, regarding two variants with different heat conductivities of the solid phase resulting in different developments in time of the temperature.
Vertical Cauchy stresses of the basic matrix at different times are depicted at the deformed landfill structure.
Example: Analysis of gas extraction system
To investigate the influence of deformation on gas flow two variants with different permeabilities are compared. After 2.2 years the extraction system is activated. The simulations are performed under isothermal conditions, implying a higher decrease in permeability in variant 2 due to compaction. At 0.5 h after activation of gas collection, the effect of gas extraction is already visible from the negative pressure close to the extraction pipe. After 33 h a larger area of the landfill cross section is under negative pressure.
Efflux of gas is depicted over time regarding both variants of permeabilities. From the obtained gas production curve it is obvious that gas production is strongly related to degradation.
Example: Development of acetate in the landfill-site