Environmental Engineering Reference
In-Depth Information
Geomechanical appraisal of the deformation potential
of a deep tunnel in a volcanic rock mass
D. simic
Ferrovial Agroman
Polytechnical University of Madrid, Madrid, Spain
J. lópez
Ferrovial Agroman
aBsTRacT: ophiolitic complexes can be defined as an association of ultra basic volcanic rocks (ultra-
mafic) and basic (mafic) constituents of the oceanic crust as a result of a phenomenon of abduction clash
between continental plates. an intricate structure in which volcanic rocks are intruded in the direction of
the schistosity of the metamorphic rocks is further complicated by large scale over thrusts which create
tectonic melanges at the base of such mega structures, affecting it by secondary tectonic contacts and
inverse faults. The whole entity is found in considerable tectonic disorder where packages of peridotites or
pillow lavas of various sizes “float” inside a sheared shale-like mass. it is understandable that tunnelling in
such a formation requires a good appraisal of the rock mass deformation potential as it will have a direct
impact in the support behaviour, particularly in the deeper sections with more than 250 m overburden.
This paper deals with the geomechanical characterisation of the heterogeneous rocks mass and the differ-
ent models employed to simulate its behaviour during the tunnel excavation and support.
1
oRThRYs MoUnTain oPhioliTic
coMPleX
- a top layer composed of sediments (mud and
chert) and sedimentary rocks, in our case the
layers of shale and chert.
- Below, a layer of compact pillow lavas with the
presence of nodules of cherts and dykes intruded
in the direction of the schistosity planes of meta-
morphic rocks. They form the basic or mafic sec-
tion of the sequence
- Below, separated from the previous layer by
a tectonic contact, a layers consisting of mas-
sive gabbros, layered gabbros and peridotites
and tectonized peridotites is encountered. This
section constitutes the ultramafic or ultrabasic
part of the complex; which has the peculiarity
of having textures similar to those of the sedi-
mentary rocks. in basal layer, the rocks with tex-
ture and/or tectonic structure are at the bottom
and separated from the massive formations by a
transition area, usually by tectonic contact.
The tunnel T-2 belongs to the e-65 highway
scheme, crossing the western slopes of “Paliovigla-
Paliokazarma-kazarma” ridge, belonging to the
othris massif in central Greece.
The macro-geological unit in which the tunnel
is located is called orthrys ophiolitic complex,
which has been widely studied from a genetic
and geological point of view as well as from the
geo-mechanical point of view by various authors
(Marinos, Verroios, Foucault, etc.). This complex
has been encountered in numerous significant
projects during which the different geological
units that comprise this formation unit have been
studied.
ophiolitic complexes can be defined as an asso-
ciation of ultra basic volcanic rocks (ultramafic)
and basic (mafic) constituents of the oceanic crust
that may appear arranged on the continental crust
as a result of a phenomenon or obduction clash
between continental plates. The orthrys ophiolite
complex shows an intricate structure in which the
pillow lavas cut a serpentinized peridotite and gab-
bro volumes are rooted in the peridotites. shear
zones are common.
The general and synthetic outline of an alpine
ophiolitic complex is as follows:
as ophiolites are associated with large-scale over-
thrusts, tectonic mélanges can be formed in the base
and at the front of such megastructures. These ophi-
olitic mélanges contain ophiolitic rocks and other
rocks of various paleogeographic origins; the whole
entity being in considerable tectonic disorder with
chaotic masses where blocks and packages of vari-
ous sizes of any kind or rock (sedimentary or vol-
canic) “float” inside a sheared soil like mass.
Search WWH ::




Custom Search