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ones that have been proposed here (c
M
= 0.30 MPa,
Φ
M
= 28.5° and e = 1700 MPa.
• in all convergences sections in pyroclastics,
certain long term flow deformations remains.
Though, this flow appears to be constant in
time, it actually has a very low speed (between
0.1 and 0.25 mm/month).
5
conclUsions
Based on the observed behavior of the pyroclastics
and the back-analysis carried out, the following
conclusions can be drawn:
• The measured convergences are compatible with
k
0
= 1.0.
• The time evolution of the convergences
measurements indicates a rheological behavior
of the ground, with a low deformation velocity.
The 100% of the deformation after the excavation
does not take place after at least 4 months.
• From the behavior of the pyroclastics high
strength parameters can be derived. Values
proposed on this paper for cohesion and friction
(c
M
= 0.30 MPa, Φ
M
= 28.5°) correspond to the
application of the failure criterion of serrano &
olalla (1999) with values β
i
= 1500 kPa, ζ
i
= 0.30
and Gsi = 85. These are high values for this type
of material.
• The elastic modulus of the pyroclastics compati-
ble with the measurements is also high “a priori”
for a compact granular material slightly welded
or not welded at all. its value is e = 1700 MPa.
it must be taken into account that this is the
unloading modulus, higher than the loading
one, which must be used for foundations.
• There are other possible combinations of values
of c
M
, Φ
M
and e of the pyroclastics, compatible
with the observed behavior of the ground.
nevertheless, in the authors´ opinion, the real
values of the ground should not be very different
from the ones proposed here.
acknoWleDGeMenTs
The authors express their gratitude to Martin Piñar
Rodriguez, site director of Works, to emilio Grande
de azpeitia, manager of TRaZas inGenieRÍa,
to
†
luis Bascones alvira (TaGsa), geologist of
the Project, to Francisco Pecino (aePo-TRaZas
consortium) head of the technical assistance dur-
ing construction of the tunnel, and to ivan García
sáez for his contribution to the translation of this
paper.
ReFeRences
aFTes (2001). “Recommendations on the convergence—
confinement method”. Paris, France.
hoek, e., carranza-Torres, c & corkum, B. (2002).
“hoek-Brown failure criterion—2002 edition”.
iTasca consulting Group, inc. (2002). Flac
2D
version
4.0. Minneapolis, Usa.
Panet, M. (1995). “le calcul des tunnels par le méthode
des curves convergence-confinement”. Presses de
l'École nationale des Ponts et chaussées. Paris,
France.
Rockscience inc. (2002). Rocklab versión 1.007.
Toronto, canada.
serrano, a. & olalla, c. (1999). “Propiedades geotécnicas
de materiales canarios y problemas de cimentaciones y
estabilidad de laderas en obras viarias”. XXii semana
de la carretera. asociación española de la carretera.
islas canarias.
