Erfahrungs- und Forschungsbericht 2012 - Ensi

Erfahrungs- und Forschungsbericht 2012 - Ensi

intact rock mass. Within the more compliant fault

zones the model suggests a significant larger EDZ

depth up to 12 m. The asymmetric distribution of

the EDZ is the result of both, the in-situ stress components

which are inclined in respect to the tunnel

axis, and the influence of the more compliant fault

zones on the stress redistribution. The increased EDZ

depth in the intact rock mass adjacent to the fault

zones suggests localized stress concentrations; as

a consequence the EDZ propagates deeper into

the rock mass. This failure behaviour is associated

with larger measurable displacements in the model.

This is consistent with the geodetic measurements

made during the construction which showed a significant

increase of the horizontal displacements in

the vicinity of the fault zones. Depth and geometry

of the EDZ are in good agreement with the results

from the seismic tomography along both sidewalls.

In addition to the above described basic case model,

a series of models with various constitutive laws

(e.g. isotropic elastic and transversal isotropic) and

a broad range of constitutive properties were analyzed.

These analyses are ongoing and will be used

to establish insights into physical sensitivities, and

for a detailed understanding of stress redistribution

associated with large-scale rock mass heterogeneities

such as fault zones.

Figure 3:

Bi-linear strength criterion

for the matrix

(S-specimen), bedding

and fault planes. Laboratory

test results

from S-specimen were

sized according to their


Additional work carried out in 2012

Beside above mentioned work and results, a series

of sub-projects were conducted in 2012. A

detailed description is beyond the scope of this

annual report. However, new insights were obtained

through a rigorous review of all laboratory

strength and deformability test data conducted in

the past 10 years from samples taken at the Mont

Terri underground research laboratory. The detailed

analysis revealed relevant findings in terms

of the influence of specimen dimensions, water

content and saturation degree on the obtained

rock mechanical properties; and thus on established

strength criteria used for numerical modeling.

In addition to this review, numerical scoping

calculations were conducted which address the

influence of variations in surface suction on the

hydro-mechanical behavior (due to temperature

and relative humidity variation in the tunnel), and

the influence of consolidation on time-dependent

lining loads (Amann et al. 2012). Furthermore, a

numerical study addressing relevant aspects and

processes underpinning the observed hydro-mechanical

and constitutive behavior was initiated.

These studies are ongoing in 2013.

National Cooperation

ENSI provides major funding of the RC experiment

and cooperates with ETH in the coordination of

this research activity. Swisstopo is the second costsharing


International Cooperation

The institutions cooperating with the Chair of Engineering

Geology at ETH and ENSI are the following:

1) Bundesanstalt für Geowissenschaften und

Rohstoffe (BGR), Germany; 2) Chevron ETC, USA.

Figure 4:

Numerical modeling

results of the excavation

damaged zone

(EDZ) around the RC


ENSI Erfahrungs- und Forschungsbericht 2012 265

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