No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Citytunneln, Malmö: Geotechnical hazards and opportunities
Abstract
Penetrating limestone in Malmo, Sweden, the underground works at Citytunneln comprise two parallel 7.8 m internal diameter railway tunnels, 6 km long, excavated with tunnel-boring machines. Triangeln Station, halfway along the tunnels, is a 30 m wide cavern with 15 m soil/rock cover and a row of pillars for central support. Malmo C Station at the northern end is an open cut-and-cover structure. There are two contracts, one for the tunnels and cavern (Lot E201) and another for Malmo C Station (Lot E101). Differing risk management techniques maintained an appropriate balance in the risk distribution. Groundwater lowering close to the harbour and the stability of adjacent historic buildings were the main hazards in E101. The design was based on the client's geotechnical interpretative report (GIR), and encountered deviations were compensated within a unit rate contract (E101). By contrast, the tunnelling risks in E201 were handled in a design build contract (Lot E201), with the contractor responsible for the GIR. The geotechnical risk management was based on contractual geotechnical reference conditions. The observational method was used successfully to mitigate geotechnical hazards as well as to exploit opportunities.
... It is often emphasised that the observational method requires a good internal culture within the project. All involved parties must together strive towards a common goal for the project to be successful (Powderham 1994, Nicholson et al. 1999, Chapman & Green 2004, Hartlén et al. 2012). Conversely, the opposite causality is also inferred; using the observational method may, in itself, promote greater motivation and teamwork within the project (Powderham 2002). ...
... Reports on successful application of the observational method (or related, less strictly defined observational approaches) have been provided in e.g. Nicholson (1996), Powderham (1998), Nicholson et al. (1999), Peck (2001, Moritz & Schubert (2009), Wu (2011), Hartlén et al. (2012), Serra & Miranda (2013), Prästings et al. (2014), Miranda et al. (2015, and in Papers A and C appended to this thesis. ...
Constructing sustainable structures in rock that satisfy all predefined technical specifications requires rational and effective construction methods. When the geotechnical behaviour is hard to predict, the European design code, Eurocode 7, suggests application of the observational method to verify that the performance is acceptable. The basic principle of the method is to accept predefined changes in the design during con-struction to comply with the actual ground conditions, if the current design is found unsuitable. Even though this in theory should ensure an effective design solution, formal application of the observational method is rare.
Investigating the applicability of the observational method in rock engineering, the aim of this thesis is to identify, highlight, and solve the aspects of the method that limit its wider application. Furthermore, the thesis aims to improve the conceptual understanding of how design deci¬sions should be made when large uncertainties are present.
The main research contribution is a probabilistic framework for the observational method. The suggested methodology allows comparison of the merits of the observational method with that of conventional design. Among other things, the thesis also discusses (1) the apparent contra-diction between the preference for advanced probabilistic calculation methods and sound, qualitative engineering judgement, (2) how the establishment of limit states and alarm limits must be carefully considered to ensure structural safety, and (3) the applicability of the Eurocode definition of the observational method and the implications of deviations from its principles.
... To be successful, the preliminary design must be chosen such that it avoids the use of costly and time-delaying contingency actions with sufficiently high probability. Over the years, successful applications of the observational method and discussions thereof have been reported [4][5][6][7][8][9][10][11][12][13][14][15][16][17]. ...
The observational method in geotechnical engineering is an acceptable verification method for limit states in Eurocode 7, but the method is rarely used despite its potential savings. Some reasons may be its unclear safety definition and the lack of guidelines on how to establish whether the observational method is more favourable than conventional design. In this paper, we challenge these issues by introducing a reliability constraint on the observational method and propose a probabilistic optimization methodology that aids the decision-making engineer in choosing between the observational method and conventional design. The methodology suggests an optimal design after comparing the expected utilities of the considered design options. The methodology is illustrated with a practical example, in which a geotechnical engineer evaluates whether the observational method may be favourable in the design of a rock pillar. We conclude that the methodology may prove to be a valuable tool for decision-making engineers’ everyday work with managing risks in geotechnical projects.
... This has led to recommendations to use design-and-construct contracts, since this limits the number of parties. Hartlén et al. (2012) emphasise the importance of good client-contractor cooperation for successful use of the observational method, based on recent experiences from a tunnel project in Malmö in southern Sweden. Despite these impediments, case studies (e.g. ...
For tunnelling in rock in Sweden, the public authorities usually set stringent requirements on low groundwater inflow to the tunnel, to minimise the risk of building settlement and the environmental impact. In order to improve this groundwater control, the potential application of the observational method in this matter was studied. A comparison was made between the actual implementation of groundwater control in the Northern Link road tunnel project in Stockholm and the definition of the observational method in Eurocode 7. The results showed that the groundwater control in the Northern Link project mainly agreed with the Eurocode. The significance of the deviations was discussed, and it was concluded that adopting the observational method for groundwater control so that it complied with Eurocode 7 would mostly entail simply a formalisation of today's procedures.
The core team that will handle the Citytunnel project in Malmö is quite experienced as they have done it before with the Øresund Crossing. The project is a fast paced one as the team has cooperation, lean project management, risk management system, and gives importance on the design and build contract (E201) for the tunnels. The JV of Bilfinger Berger, Per Aarsleff, and the E Pihl &Søn was assigned to build the running tunnels, cross passages and the cavern for the Triangeln station. The challenge for them was on how to build the twin 7.9m i.d. running tunnels from Holma to the Triangeln station cavern. As for the cross passage construction, different approaches were used by the contractor to combine the segmental rings that will be used.
The paper forms the first part of an introduction to the SHE, a physically-based, distributed, catchment modelling system produced jointly by the Danish Hydraulic Institute, the British Institute of Hydrology and SOGREAH (France) with the financial support of the Commission of the European Communities. The SHE developed from the perception that conventional rainfall/runoff models are inappropriate to many pressing hydrological problems, especially those related to the impact of man's activities on land-use change and water quality. Only through the use of models which have a physical basis and allow for spatial variations within a catchment can these problems be tackled. The physical basis and flexible operating structure of the SHE allows the model to use as many or as few data as are available and also to incorporate data on topography, vegetation and soil properties not normally included in catchment models. It does not require a lengthy hydrometeorological record for its calibration and its distributed nature enables the spatial variability in catchment inputs and outputs to be simulated. However, the large amount of data required by the model means that new operation methodologies must be evolved. Thus spatial scale effects or simply a lack of data may create significant uncertainties in the values of the catchment parameters used in a simulation. These uncertainties will give rise to corresponding uncertainties in the predictions. However, the SHE is able to quantify these uncertainties by carrying out sensitivity analyses for realistic ranges of the parameter values. Even when there is a lack of data, therefore, the SHE can act as a valuable “decision-support system”.
The paper forms the second part of an introduction to the SHE, a physically-based, distributed catchment modelling system produced jointly by the Danish Hydraulic Institute, the British Institute of Hydrology and SOGREAH (France) with the financial support of the Commission of the European Communities. The SHE is physically-based in the sense that the hydrological processes of water movement are modelled either by finite difference representations of the partial differential equations of mass, momentum and energy conservation, or by empirical equations derived from independent experimental research. Spatial distribution of catchment parameters, rainfall input and hydrological response is achieved in the horizontal by an orthogonal grid network and in the vertical by a column of horizontal layers at each grid square. Each of the primary processes of the land phase of the hydrological cycle is modelled in a separate component as follows: interception, by the Rutter accounting procedure; evapotranspiration, by the Penman-Monteith equation; overland and channel flow, by simplifications of the St. Venant equations; unsaturated zone flow, by the one-dimensional Richards equation; saturated zone flow, by the two-dimensional Boussinesq equation; snowmelt, by an energy budget method. Overall control of the parallel running of the components and the information exchanges between them is managed by a FRAME component. Careful attention has been devoted to a modular construction so that improvements or additional components (e.g. water quality and sediment yield) can be added in the future. Considerable operating flexibility is provided through the ability to vary the level of sophistication of the calculation mode to match the availability or quality of the data.