COUPLING OF MODELS FOR ASSESSMENT OF HYDROGEOLOGICAL RISKS IN UNDERGROUND CONSTRUCTION

Groundwater drawdown induced by leakage can affect large areas surrounding the underground facility and subsequently induce risks such as subsidence and subsidence damages to the built-up environment. These risks can be reduced by implementing risk mitigation measures. The relationships between leakage and various effects and their consequences can be described by a chain of events that need to occur for the leakage to cause damage. The nature and severity of the consequences of damage is determined by the dynamic interaction between the different components in the cause–effect chains, e.g. magnitude of leakage, the groundwater system´s response to stresses and the sensitivity to stresses of the objects at risk. To evaluate the economic profitability of risk mitigation measures, several models describing the separate events of the dynamic cause-effect chain (e.g., leakage, groundwater drawdown, subsidence, and damage) their consequence (damage) costs and the implementation costs of measures must be coupled. Current research for predicting future behavior of the system is to a large extent directed toward the individual parts of the cause–effect chain, which create a research gap for the development of coupled methods as parts of a comprehensive risk assessment. We present a case study that demonstrate how several models describing the different parts of the chain of events can be used to assess the economic profitability of investing in different risk mitigation measures in an urban area with subsidence prone soils. The chain of coupled models constitute data driven models, an analytical solution model, as well as models developed based on expert elicitation. The usage of expert elicitation demonstrate how models can be developed when data is limited, unreliable, too costly to obtain, or unobtainable in order to enable a comprehensive risk assessment. The result from the case study was used in the tunnel project as support for decisions on implementation of risk mitigation measures.