Face stability improvement by advance drainage via pilot tunnel

Zingg, Sara; Bronzetti, D; Anagnostou, G.

doi:10.1201/b14769-97

Cited by 1 publication

(2 citation statements)

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“…2c,d), was investigated by [7]. Even a very small diameter pilot tunnel causes such a big pore pressure relief that the face of the main tunnel may be stable without additional auxiliary measures.…”

Section: Imperfect Drainagementioning

confidence: 99%

“…Die Anwendung der vorauseilenden Drainage via Pilotstollen, der entweder innerhalb oder außerhalb des Tunnelprofils liegen kann (Bild 2c) d)), wurde in [7] untersucht. Schon ein Pilotstollen mit sehr kleinem Durchmesser verursacht einen so großen Porenwasserdruckabbau, dass die Ortsbrust des Haupttunnels bei der Aufweitung ohne weitere Maßnahmen standsicher sein kann.…”

Section: Case Study -Lake Mead Intake No 3 Tunnelunclassified

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On the stabilizing effect of advance drainage in tunnelling / Über die statische Auswirkung der vorauseilenden Gebirgsdrainagen im Tunnelbau

Anagnostou

Zingg

2013

Geomechanics and Tunnelling

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The paper reviews the favourable effects of advance drainage with respect to three tunnel engineering problems in water-bearing ground: the stability of the tunnel face, the stability of grouting cylinders in geological fault zones and the convergences in squeezing ground. In a high permeability ground, advance drainage improves the stability of the tunnel face because it reduces the pore pressures and their gradients in the ground ahead of the face. If the ground exhibits a low permeability, advance drainage increases its short-term shear resistance and thus the short-term stability and the stand-up time of the face. In fault zones with flowing ground, tunnel advance is often possible only after strengthening and sealing the ground around the tunnel by grouting. As the permeability of the grouted body is very low in relation to that of the surrounding untreated ground, large seepage forces may develop inside the grouted body. Systematic drainage reduces the pore pressure gradient within the grouted body, improving thereby its stability while reducing the risk of inner erosion and uncontrollable water and mud inrush. Squeezing ground usually exhibits low permeability and a pronounced timedependent behaviour. It is well known that high pore pressures favour the development of squeezing. The pore pressure relief consolidates the ground, increasing as a result its undrained shear strength. This is favourable with respect to the short-term convergences in the vicinity of the tunnel heading. Advance drainage is favourable also with respect to the long-term ground response because it eliminates the high pore pressure gradients associated with the first stages of the consolidation process around the opening.

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Section: Imperfect Drainagementioning

confidence: 99%

Section: Case Study -Lake Mead Intake No 3 Tunnelunclassified