Tunnel Face Stability and the Effectiveness of Advance Drainage Measures in Water-Bearing Ground of Non-uniform Permeability
Open access
Date
2018-01Type
- Journal Article
Abstract
Non-uniform permeability may result in complex hydraulic head fields with potentially very high hydraulic gradients close to the tunnel face, which may be adverse for stability depending on the ground strength. Pore pressure relief by drainage measures in advance of the tunnel excavation improves stability, but the effectiveness of drainage boreholes may be low in the case of alternating aquifers and aquitards. This paper analyses the effects of hydraulic heterogeneity and advance drainage quantitatively by means of limit equilibrium computations that take account of the seepage forces acting upon the ground in the vicinity the tunnel face. The piezometric field is determined numerically by means of steady-state, three-dimensional seepage flow analyses considering the heterogeneous structure of the ground and a typical advance drainage scheme consisting of six axial boreholes drilled from the tunnel face. A suite of stability analyses was carried out covering a wide range of heterogeneity scales. The computational results show the effect of the orientation, thickness, location, number and permeability ratio of aquifers and aquitards and provide valuable indications about potentially critical situations, the effectiveness of advance drainage and the adequate arrangement of drainage boreholes. The paper shows that hydraulic heterogeneity results in highly variable face behaviour, even if the shear strength of the ground is constant along the alignment, but ground behaviour is considerably less variable in the presence of advance drainage measures. Show more
Permanent link
https://doi.org/10.3929/ethz-b-000199208Publication status
publishedExternal links
Journal / series
Rock Mechanics and Rock EngineeringVolume
Pages / Article No.
Publisher
SpringerSubject
Advance drainage; Tunnel face stability; Limit equilibrium; Non-uniform permeability; Anisotropy; Fault zone; Aquifer; AquitardOrganisational unit
03655 - Anagnostou, Georgios / Anagnostou, Georgios
02607 - Institut für Geotechnik / Institute for Geotechnical Engineering
Notes
It was possible to publish this article open access thanks to a Swiss National Licence with the publisher.More
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