Geothermal modelling should form a standard part in any permafrost design. Three aspects of geothermal modelling need special attention and must be subject to sensitivity analyses:
o Climate boundary conditions, o Geothermal properties, and o Initial conditions.
The more measured climate data, including air temperature, snow depth, solar radiation, wind speed and direction, and precipitation are available, the more accurate soil thermal properties can be calibrated and initial conditions established. Three-dimensional effects (Gruber et al., 2004) in mountainous terrain can be particularly challenging to incorporate accurately and therefore sufficient data must be available to obtain the required confidence in the model.
A long-term, past climate average should be utilised to obtain steady state conditions before measured climate conditions are applied. The measured ground temperatures as well as active layer thicknesses are to be compared with the modeled data and the model parameters adjusted accordingly. Without proper determination of initial conditions, predictions of subsequent responses are very uncertain.
Different scenarios should be adopted for long-term geothermal modelling that account for uncertainties in climate change predictions. Not only will air temperatures change in the future, additional climate factors must be represented, too. These form the basis for the sensitivity analysis that is crucial for any structure that depends on the integrity of a foundation where future changes are difficult to forecast. Possible long-term changes in the ground geothermal properties must be included in the transient modelling. It is recommended to alter initial conditions to study their effect on long-term behaviour. This step is important when no or only little data are available to calibrate the model and obtain initial conditions. In summary, the fewer climate and ground temperature data that are available, the greater the variations and range must be evaluated during the geothermal modelling phase.
Was this article helpful?