On the role of constitutive behaviour in the response of squeezing ground to tunnelling
Rock Pressure, Tunnel, Tunnelling, Gotthard, Gibraltar Tunnel
Triaxial testing is the main source of information in order to understand the mechanical features of squeezing ground. Despite the complexity of the squeezing mechanism and the behaviour observed under relatively simple loading conditions, most of previous research work and engineering design practice considers the ground as a linearly elastic, perfectly plastic material obeying the Mohr-Coulomb yield criterion. While the MC model is capable of predicting the final strength and post-failure volumetric behaviour of the squeezing rock, it cannot map some potentially important pre-failure features or the occasionally observed contractant plastic deformation. In addition, the MC model usually leads to an overestimation of the strength under undrained conditions, which is unsafe for tunnel design.
The present thesis mainly addresses the influence of constitutive modelling on predictions about the response of squeezing ground to tunnelling in order to provide some general guidelines for basic engineering analysis. This objective is achieved by investigating the behaviour of squeezing rocks theoretically and experimentally, using samples from several tunnel projects, including the Gotthard base tunnel and the planned Gibraltar strait tunnel.
For further information see extract.
- Buchreihe: Veröffentlichungen des Instituts für Geotechnik (IGT) an der ETH Zürich Volume 250
- Auflage: 1., 2017
- Seiten: 204 Seiten
- Abbildungen: zahlreiche Abbildungen, farbig
- Format in cm: 21,0 x 29,7
- Einbandart: PDF
- ISBN: 978-3-7281-3861-3
- DOI: 10.3218/3861-3
- Sprache: Englisch
- Lieferstatus: gedruckte Ausgabe vergriffen, als eBook lieferbar
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Tunnelling, Squeezing, Schistosity, Heterogeneity, Analytical Solution, Numerical Modelling, Segmental Lining
The magnitude of squeezing deformations in tunnelling often varies over short distances, even if there is no obvious change in the construction method, in the depth of cover, in the lithology or rock structure. As long as the reasons for the variability are not known, the tunnelling-induced convergences cannot be predicted with sufficient reliability. Reliable predictions, however, are important for determining the temporary support or the excavation diameter. Otherwise, large-scale tunnel repairs may be necessary, which can cause delay and additional costs due to remedial actions as well as due to the enforced interruption of other operations in progress at the same time.
Tunnelling, Tunnel Jacking, Ground Stability, MC Model, MCC ModelThis thesis investigates the problem of time-dependent stability of geotechnical structures (such as trenches or tunnels) in medium- to low-permeability water-bearing grounds, typically clayey or silty soils. The peculiarity of these soils is that they respond to excavation with a delay. The time-dependency can be traced back to the swelling process triggered by the dissipation of the excavation-induced negative excess pore pressures. Unstable conditionsmay necessitate improvement or reinforcement of the ground or the application of a support (e.g. by compressed air or pressurized bentonite slurry in the case of tunnel face). As such measures may present economical and operational disadvantages, the question of whether and for how long the excavation can remain stable without support is of great practical relevance. The stand-up time (time lapsing between end of the excavation and the occurrence of failure), and thus the feasibility of refraining from ground reinforcement, improvement or support, depends essentially on soil strength and permeability.
Advance Drainage, Drainage Boreholes, Tunnel, Face Stability,
Limit Equilibrium, Fault Zone, Drainage Capacity, Equivalent Hydraulic
Conductivity, Borehole Casing, Lead-Time, Groundwater Drawdown, Settlement, Inflow, Grouting Body, Displacement, Characteristic Line