Quantification of tunnel leakage and accompanied subsidence by means of numerical modelling
The greater Oslo area, which has been subject to excessive building an underground construction in the last two decades, is a geological challenging area.
Fast isostatic uplift in the late Pleistocene-Holocene led to sedimentation of clay with thickness up to several ten meters above a rudimentary glacio-fluvial layer. This led to a situation in which most buildings found on sedimentary layers are built on clay (or, in worse cases, its thixotropic variation, quick clay).
Due to the pore pressure sensitivity of the masses related to settlement, and consequently building damages, ranging from small-scale housing to critical infrastructure (Sundell et al., 2019).
Therefore great caution has to be taken for tunnel construction leading to:
- High building costs due to watertight construction in areas of increased risk
- Inacceptable uncertainty related to evaluation of settlements due to leaking water into the tunnel.
- Inchoate evaluation of possible long time damages at buildings and infrastructure
Analytical or simple block model assessments are not suitable for a detailed analysis and therefore the risk analysis has to be carried out using numerical models. Several studies have been carried out in Modflow (URL 1 and 2). Due to the nature of the code it cannot reproduce complex underground/geological structures and therefore is subject to simplification which is insufficient.
We, therefore, suggest the use of the more versatile finite element software package FeFlow. Until recently it was not possible though to model hydro-mechanical coupled models in FeFlow but is now possible with newly developed (open source) plugins (Pham et al., 2019).
The master project will be related to one of the major infrastructure projects in Norway, the new metro line in Oslo, which gives the candidate the possibility to get insight into big projects while benefiting from extensive data to be used for the master project.
The candidate will use state-of-the-art numerical models to study hydrogeology and its coupling with rock deformation, and apply the models to a large scale geotechnical application. Knowledge or the will to learn FeFlow and ArcGis Pro are seen as essential to solve the problem formulation.
The successful candidate will be supported from senior staff at Multiconsult and a professor at the Department of Geosciences. Due to the novelty of the research, we assume dissemination in a journal article and/or conferences which will be supported as well.
Literature (illustrative examples):
- Chen, X.X., Luo, Z.J., and Zhou, S.L., 2014. Influences of soil hydraulic and mechanical parameters on land subsidence and ground fissures caused by groundwater exploitation. Journal of Hydrodynamics, Vol. 26, No. 1, p. 155–164.
- Lindstrøm, M., & Kveen, A. (2005). Tunnel investigtion and groundwater control.
- Pham, H. T., Rühaak, W., Schuster, V., & Sass, I. (2019). Fully hydro-mechanical coupled Plug-in (SUB+) in FEFLOW for analysis of land subsidence due to groundwater extraction. SoftwareX, 9, 15-19. https://www.sciencedirect.com/science/article/pii/S2352711018301286#fig5
- Sundell, J., Haaf, E., Tornborg, J., & Rosén, L. (2019). Comprehensive risk assessment of groundwater drawdown induced subsidence. Stochastic Environmental Research and Risk Assessment, 33(2), 427-449. https://link.springer.com/article/10.1007/s00477-018-01647-x
- Terzaghi, K., (1925). Principles of Soil Mechanics: IV-Settlement and Consolidation of Clay. Engineering News-Record.
- URL 1: http://kth.diva-portal.org/smash/record.jsf?pid=diva2%3A1290070&dswid=-1031
- URL 2: https://pubs.usgs.gov/of/2003/ofr03-233/pdf/ofr03233.pdf