Comparison of Modelling Strategies for Ground Settlements due to Groundwater Drawdown Multi-criteria analysis for comparison of three software packages

Examensarbete för masterexamen
Infrastructure and environmental engineering (MPIEE), MSc
Ögger, Frida
Johansson, Linnea
When performing construction projects below the groundwater level, groundwater leakage into the construction can occur, which can lead to settlements. This Mas ter’s thesis aims at comparing three different software packages for calculation of settlements caused by groundwater drawdown in an aquifer situated below com pressible soils. The different software packages used are: a stochastic settlement model that considers creep effects and parameter uncertainties, the Soft Soil Creep model available in Plaxis 2D and the Chalmers model with creep available in GS Set tlement. To evaluate the appropriateness of them, settlement calculations for both 1D and 2D soil models are performed, together with a multi-criteria analysis (MCA). The 1D modelling results show that all three approaches exhibit the same elastic and elasto-plastic behaviour. For comparison of the creep behaviour between Plaxis 2D and GS Settlement, differences arise due to model formulations. GS Settlement seems to predict lower creep settlements than Plaxis for stress states around the preconsolidation pressure. For drawdowns that highly exceed the preconsolidation pressure, GS Settlement instead predicts higher settlements compared to Plaxis. The stochastic settlement model does not include creep effects, but the additional deformation is captured by the parameter uncertainty interval for drawdowns near the preconsolidation pressure and higher. When comparing 2D effects of consol idation, the ability for the stochastic settlement model to capture the additional settlements predicted by Plaxis 2D is ambiguous. The results in this thesis highlight the differences between the three software pack ages. The MCA shows that the stochastic settlement model has a good capability in handling spatial uncertainties, but is disadvantageous due to the low level of intu ition. Plaxis can handle complex geometries, but the calculation is time demanding. GS Settlement is more intuitive with lower calculation effort required, but lacks the ability of performing calculations with complex geometries. The MCA further em phasises that the ability to implement the theoretical framework of a groundwater drawdown together with modelling a drawdown over a large area is considered of high importance. To make it less subjective, further prerequisites which define the features of the project is needed. Hence, this comparison can serve as a support for future projects to achieve a versatile analysis in a structured way.
Ground settlements , Multi-criteria analysis , Analytical modelling , Groundwater drawdown , Soft clays , Plaxis 2D , GS Settlement
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