Risk Assessment of Groundwater Drawdown in Subsidence Sensitive Areas

Doctoral thesis, 2018

Groundwater leakage into sub-surface constructions can result in drawdown, subsidence in compressible materials, and costly damage to buildings and installations. When planning for sub-surface constructions where there is a risk for land subsidence due to groundwater drawdown, the need for safety measures must be carefully evaluated and managed. Since the sub-surface consists of heterogeneous and anisotropic materials, which cannot be fully investigated in all aspects, decisions regarding safety measures must be taken under uncertainty. In this thesis, a generic framework is presented on how to assess the risk of groundwater drawdown-induced subsidence (Paper I). As specific tools for modelling uncertainties in the groundwater drawdown – subsidence – damage chain, a method for probabilistic modelling of bedrock levels and soil stratification (Paper II) and a method for probabilistic modelling of ground subsidence to a large spatial extent (Paper III) are presented. These are combined with a probabilistic groundwater model and cost functions to calculate the economic risks of subsidence damage between different design alternatives (Paper IV). Finally, a novel method for economic valuation of hydrogeological information is presented in Paper V. The methods presented can distinguish between low and high-risk areas, identify the alternative with the highest net benefit compared to a reference alternative, and estimate the expected benefit of additional information. The methods have been demonstrated to provide useful support for decision-making and communication tools when assessing the risk of large-scale groundwater drawdown-induced subsidence in different infrastructure projects in Sweden.