Quantifying building damage induced by underground construction at city scale

Doktorsavhandling, 2025

Leakage of groundwater into underground construction may lead to time-dependent reduction of pore pressures.
The resulting subsidence can increase the risk of flooding and damage to structures, causing significant costs to society and individuals. This is especially common in areas with deformation-sensitive clays, typical to Scandinavia. The pore pressure reduction caused by leakage to tunnels built in fractured rock, called underdrainage, is common in Scandinavia and may affect a large area of influence, requiring expensive mitigation measures. Planning for such mitigation measures to prevent significant damage involves a trade-off between costs and benefits of their implementation. We need an understanding of the processes involved in the large-scale subsidence due to underdrainage, and the potential damage. The problem is highly complex, uncertain, and coupled. Thus, a rigorous modelling framework was developed as part of this thesis.

A 2D hydro-mechanically coupled finite element (HMFE) model with an advanced rate-dependent constitutive model was used to assess the influence of key parameters affecting the time-dependent (greenfield) settlements caused by underdrainage. The time-dependent results from the HMFE model were then used along with hydro-stratigraphy as training and validation data for a metamodel, which produced settlements on a 3D hydro-stratigraphic domain. The results of the metamodel were used as input for a large-scale building damage model developed to calculate damage parameters based on various damage criteria. In urban settings, greenfield predictions potentially result in over-prediction of damage, as most buildings on soft deposits are built on piled foundations. Thus, the influence of floating piles was considered via axisymmetric finite element simulations, providing modification factors that can be applied to greenfield settlements for older piled buildings.

The developed models were applied to the case of the construction of an underground railway station in Gothenburg, Sweden, expected to affect a confined aquifer in an area with ongoing background creep settlements. Hypothetical scenarios of uniform pore pressure reduction under the soft clay deposit, and the subsequent consolidation and creep in the soft clay, were simulated to determine the magnitude of settlements at different time intervals. The results showed dependency on time and stratigraphy, where the transitional areas between the soil and rock are most prone to settlements in short term, influenced by the overconsolidation ratio (OCR). The predicted settlements, as well as the modified settlements due to the existence of floating piles were shown to be highly time-dependent, due to the slow consolidation associated with underdrainage in deep clay layers. Furthermore, the results also show that the estimated damage is highly dependent on the chosen damage criteria. Based on the results, only damage parameters derived from differential settlements should be used in early damage assessments.