Uncertainty and sensitivity analysis in soil strata model generation for ground settlement risk evaluation

Abstract: Popular summary: Ground settlement due to groundwater drainage during construction is important to be considered since ground settlement may cause severe building damages. The calculation of ground settlement contains several parameters with uncertainties, e.g., soil layer thickness and elevations, compression and consolidation properties of different soils. If the uncertainties in the parameters are defined, the uncertainties in ground settlement could be estimated. By addressing the most influential parameters on the ground settlement in a certain area, the uncertainties in the ground settlement could be decreased. In this thesis, a three dimensional soil layer model was generated for ground settlement risk evaluation purpose. The accurate prediction of soil layers around the construction site could help better estimation of ground settlement. The uncertainties in the soil layer model were quantified and then the soil layer model was integrated with two other models (groundwater and ground settlement model) for the ground settlement risk evaluation. The case study site was located in Motala, Sweden where a pedestrian tunnel was considered to be built. The soil layer model was interpolated from borehole data - holes drilled into the ground for soil layer investigation. The interpolation technique used here was called kriging. The uncertainties in the soil layer model came from the interpolation process and were quantified. The risk evaluation of the ground settlement was carried out by Monte Carlo simulation which is a kind of stochastic modeling method. The resulted soil layer model could show soil layers formation at any specified site. The quality of interpolation was largely dependent on the amount of boreholes. The soil layer model needed to be adjusted manually since sometimes the interpolated soil layers overlapped each other. The ground settlement risk evaluation results illustrated the risk areas for building damage where the calculated ground settlement exceeded critical values. The most influential parameters on ground settlement were found varied in different places. More efforts and resources could be spent on these parameters to decrease the unacceptable risks. The kriging method used here was a sophisticated method and there is room for improvements.