1st International Congress on Tunnels and Uunderground Structures in South-East Europe „USING UNDERGROUND SPACE“
April 7-9, 2011, Dubrovnik, Croatia
Ionia Odos: Tunnelling through undisturbed anisotropic flysch
formation
Paraskevi YIOUTA-MITRA, National Technical University of Athens, Greece antipaxos@metal.ntua.gr
Chryssanthos STEIAKAKIS, General Consulting Ltd. “ISTRIA”, Greece, steiakakis.chrys@istria.gr
Dimitris MERZIOTIS, General Consulting Ltd. “ISTRIA”, Greece, merziotis.dimitris@istria.gr
Pavlos P. NOMIKOS, National Technical University of Athens, Greece, nomikos@metal.ntua.gr
Alexandros I. SOFIANOS, National Technical University of Athens, Greece, sofianos@metal.ntua.gr
Summary
Ionia Odos is one of five major highway concessions currently in progress in Greece. It contains
several tunnels, one of which is the Kalydona tunnel, recently excavated with final lining
installation currently in progress. The project area is within post-alpine sediments of flysch, found
significantly stronger than other flysch tunnelling projects in Northern Greece. This behaviour
allowed for light support in the tunnel and only small scale failures at the periphery of the tunnel
were expected and observed, caused by loading direction changes with respect to well developed
bedding planes. The main features of the Kalydona tunnel are hereby presented and the effect of
rock strength anisotropy on the tunnel response examined theoretically, numerically and compared
to actual behaviour as it was monitored during the construction.
Keywords:
case history, drill and blast, anisotropic rock, flysch, ubiquitous joint model.
1. Introduction
Rock anisotropy occurs due to genetic characteristics such as sedimentation layering and
metamorphic schistosity as well as due to the presence of secondary discontinuity systems in an
otherwise isotropic rockmass. The properties of the rockmass discontinuities, whatever their origin
may be, are the definitive component that, combined with a variable loading direction, causes rock
strength anisotropy.
Wittke [1] showed that the overstressed zones around a tunnel depend on the anisotropy of the
rock mass, Amadei and Pan [2], that the gravity-induced horizontal stresses depend on several
parameters such as the type, degree and orientation of the rock anisotropy with respect to the
ground surface. According to Gerrard [3], intact rock anisotropy is stress dependent with a
decrease in anisotropy associated with an increase in confinement. The stress dependency of rock
anisotropy implies that linear elasticity may be of limited value when describing the deformability
of anisotropic rocks and that it should be replaced by non-linear elasticity or more complex
constitutive behavior if permanent deformation occurs. Acceptable predictions of rock behavior can
still be achieved assuming linear anisotropic elasticity as long as the selected rock properties are
determined in a stress range comparable to what is expected in situ. Being able to account for the
directional character of anisotropic rocks instead of assuming them to be isotropic, as has often
been done in the past, is certainly a step in the right direction (Amadei [4]).
Underground excavation in rock always deals with variable loading direction since a secondary
stress field arises parallel to the excavation boundary. Moreover, in situ rock is hardly isotropic or
continuous and jointed rock as compared to intact rock shows increased deformability in directions
1st International Congress on Tunnels and Uunderground Structures in South-East Europe „USING UNDERGROUND SPACE“
April 7-9, 2011, Dubrovnik, Croatia
normal to the planes of weakness. In the event of a shallow tunnel combined with systematic
joint/bedding that allows for a transversely isotropic material, then critical situations are expected
mainly due to joint slip.
The Kalydona tunnel is a typical such case where the bedding strikes parallel to the tunnel axis and
dips with very small or zero angle. The features of the tunnel are presented in the following
paragraphs.
2. Kalydona Tunnel
2.1
Location
Kalydona twin road tunnel is located in the central-western part of Greece, close to the RionAntirion and at 8km distance from Messolonghi.
It is part of the 159.4m Ionia Odos Highway that
connects Antirion to Ioannina. The area of the
tunnel is characterized by an acute hilly
morphological relief covered by sparse to locally
dense shrubby vegetation and is located at the
Kalydona
south end of Arakinthos Mountain. The absolute
Tunnel
elevation at the alignment area varies between
+50 and +180 approximately. The relief of the
area is influenced by the structure of inclined
geological layers, dip to the NE-E, with low
inclination varying from 10° to 25°. The
structure of the tunnel has a general direction
NE-SW, length of 1197.5m and 1190.3m for left
Fig. 1 Kalydona Tunnel location
2.2
and right branch respectively and a maximum
overburden thickness of 100m. The distance
between the two branches is 28m (Istria [5]) .
Geological Setting
The wider project area is structured by geological formations that belong to the alpine substratum
of the Ionia geotectonical unit and by post-alpine formations that overlie in discordance. The
Ionian flysch is the main formation encountered during the tunnel excavation, made up of
continuous intercalations of sandstone and siltstone layers.
A ravine in the middle of the
alignment in the N-S direction was
initially attributed to the activity of
faults. However, the geotechnical
investigation that was undertaken in
the area (boreholes ΒΤ1-203Α, ΒΤ1204 & ΒΤ1-205) showed that the
sequence of the formations is
undisturbed and that the creation of
the ravine in the narrow area is due
to the erosion of the siltstone phase
of flysch.
Along the tunnel, the intercalations of
siltstone – sandstone layers are
uniformly dipping North – East. No
major faults were mapped or
Fig. 2 Flysch intercalation found in borehole BT1-203A
eventually found during excavation.
Minor faulting was present with light
tectonic activity that produced three and four joint systems. The predominant joint system was the
bedding and the additional systems were found to be shear sub vertical joints. Details of
1st International Congress on Tunnels and Uunderground Structures in South-East Europe „USING UNDERGROUND SPACE“
April 7-9, 2011, Dubrovnik, Croatia
microtectonics are given in Table 1. Most of the joints were found to be smooth to lightly rough
and empty. Closer to the surface the joints were found to be smooth and infilled with weathered
material from the parent rock such as silt, sand and clay.
Table 1: Tectonic Diagrams close to the entrance portal (TD1) and the exit portal (TD2)
TD1
B
J1
J2
J3
Tunnel
Dip/dip
direction
24/060
81/175
88/126
66/262
N062E
TD2
N
Orientations
ID
Bedding
J3
Tunnel
J2
W
E
J1
B
J1
J2
Dip/dip
direction
17/066
85/163
70/246
N
1
24 / 060
2
81 / 175
3
59 / 238
4
66 / 262
Equal Angle
Lower Hemisphere
4 Poles
4 Entries
Tunnel
Length/Spacing/Aperture
[m]
3-10/0.4-1.0/1-2
1-3/0.5-1.0/1-2
1-3/0.5-1.0/1-2
1-3/0.5-1.0/1-2
Orientations
Dip / Direction
ID
Bedding
TUNNEL
W
E
J2
N074E
S
J1
Dip / Direction
1
17 / 066
2
85 / 163
3
70 / 246
Equal Angle
Lower Hemisphere
3 Poles
3 Entries
S
Sandstone layers are found with varying thickness, from thickly to medium bedded, medium to
coarse grained particles and light gray colour when freshly excavated. Siltstone layers are found
mostly as medium to thinly bedded of fine grained particles not seen by the eye, dark gray to
greenish colour.
Four main lithologies have been foreseen and encountered:
a) Fi.st: This is a layer where sandstone prevails, developing in great thickness (30 to 90 m), for
the scale of the project. Layers appear medium to thick-bedded with thickness 0.3 – 1.0 m.
Very frequently, the continuance of the lithology is interrupted by thin interpolations of
siltstone layers or siltstone and thin-bedded sandstone alternation layers, whose thickness
does not exceed 1m. These thinner layers within sandstone benches appear compressed due
to reduction of the layer thickness or unwedging with indications of inner creeping, usually
jointed. This fact is locally giving the impression of a discordant deposit due to differences to
measured layer inclinations. In reality, that is due to the different behaviour of the formations
in various stress fields that acted in the area because of their different lithology. In many
cases, the creeping observed in the weaker but more plastic layer of siltstone causes faulting
and rupturing to massive layers that cannot follow the deformation. These ruptures, in most
cases, are classified in co-sedimentation tectonic, since, as observed, their continuity is
interrupted by the deposit of the overburden. The thickness of the formation is at 30m at the
entrance but reaches
b) Fi.sl,st: In this case siltstone and sandstone alternate in layers of 0.1 – 0.2 m (Fig. 2).
Sometimes thicker layers appear in the formation, where flysch phases prevail. Forms of the
co-sedimentation tectonics are rarer in this layer, given the fine-bedded nature of sandstone
that follows more readily the deformation of siltstone layer.
c) Fi.sl2: This is a layer where the lithological elements of siltstone prevail over sandstone that
contributes only with interspersed layers of 0.02 – 0.1m in the siltstone environment.
d) Fi.sl1: It is a layer that consists of fine-bedded siltstone.
2.3
Hydrogeologic conditions
The entire sandstone – siltstone rock mass is characterized by low to very low hydraulic
permeability. Although sandstone is of higher permeability than the siltstone layers, the continuous
intercalations of these two materials renders the permeability of the rock mass highly anisotropic;
in a normal to the jointing direction it is governed by the lower permeability material which is the
siltstone; in the direction tangent to the joints, the permeability of the sandstone dictates the flow.
The tunnel has been mainly excavated in dry conditions except in the entrance (Fig 3), where
water seeps from the sandstone intercalations and the middle of the tunnel where the
impermeable siltstone layer underlying sandstone acts as a hydrogeological boundary.
1st International Congress on Tunnels and Uunderground Structures in South-East Europe „USING UNDERGROUND SPACE“
April 7-9, 2011, Dubrovnik, Croatia
The characteristics of the water flow
are low pressure and slow drainage
and can be attributed to the low
overburden and permeability (~of
k=4-6x10-8 m/sec). The limited water
tables recharge after heavy rain falls
and drain again slowly without
producing any stability problems. The
water inflow maximum was 5
m3/m/24h and was dealt with
drainage holes.
2.4
Geotechnical evaluation
The geotechnical conditions along the
tunnel were evaluated based on the
geological mapping of the tunnel,
geophysical investigation (electrical
Fig. 3 Water seeping from sandstone (Fi.st) layer interrupted by a
tomography) and eight sampling
thin siltstone layer (Fi.sl) at the entrance portal, few hours after
boreholes executed prior to excavation,
rainfall.
with depths ranging from 20 to 131m.
The borehole samples were further subjected to several laboratory tests such as mineralogical
analysis from scanning electron microscopy (SEM), discontinuity shear test, slake durability,
unconfined compressive strength, point load test, Brazilian test etc. Q, RMR and GSI evaluation
was conducted from the combination of field and borehole information. The rock mass along the
tunnel was accordingly subdivided in categories based on classification but also considering the
type of predominant rock, lamination thickness and jointing characteristics according to RQD
values.
The four rock mass categories are
contained in Table 2 along with their
A
B
C
D
main properties. The unconfined
70-100
70-100
40-60
40-60
compression strength of intact rock
Sa
Si
Sa
Si
(σci) was estimated as a weighted
17.5-75
8.75-37.5
4.44-23.33
1.48-5.83
average from the individual rocks
65-78
52-67
50-63
42-53
forming
the
intercalation.
The
55-65
50-65
65-80
40-50
estimation
of
the
rock
mass
15-20
50-55
50-55
15-20
parameters such as unconfined
compressive strength (σcm), rock mass
2-5
11-15
15-25
2-3
modulus Erm, rock mass cohesion crm
20-25
10-15
10-15
3-6
and friction υrm were estimated with
55-57
40-42
50-55
35-40
the use of the GSI classification
1.0-2.5
0.5-1.0
0.7-1.3
0.3-0.4
system and the Hoek – Brown failure
The parameters were also verified with other empirical correlations.
Table 2 Rock mass categories and geotechnical properties
Rock Mass
RQD
Lithology
Q
RMR89
GSI
σci (MPa)
σcm (MPa)
Erm (GPa)
υrm (o)
crm (MPa)
criterion.
Figure 4 depicts the longitudinal section of the right bore, the geological formations and rockmass
categories as well as the location of the investigation drills.
Figure 4 Right Bore Longitudinal section of Kalydona Tunnel
1st International Congress on Tunnels and Uunderground Structures in South-East Europe „USING UNDERGROUND SPACE“
April 7-9, 2011, Dubrovnik, Croatia
3. Excavation and support measures
3.1
Proposed excavation and support
Considering the high quality of the rock mass, limited joints and medium strength, drill and blast is
selected as the most cost effective excavation method. The tunnel is excavated as top heading and
bench and the round lengths are dependent on the rock mass category encountered along the
tunnel. Table 3 contains proposed excavation and support measures, which are successfully
applied with few adjustments.
The primary support has been determined on the basis of a safe, economical and appropriate
support system for each rock mass category encountered. The significant self-supporting
properties of the rock mass have
been used as the major support
Table 3 Rock mass categories and primary support
element and enhanced mostly by
protecting the exposed rock mass
Rock Mass
A
B
C
D
from weathering, especially siltstone
Step (top heading)
2.5-3.0
2.0-2.5
1.5-2.0
1.5-2.0
intercalations and keeping tightly in
Shotcrete (cm)
10
12
16
18
place the key rock block elements
40
40
Fibres (kg/m3)
40
40
from moving or detaching. The main
4
4
Bolt length
3
4
support elements are reinforced with
St.x2.0
St.x2.0
Bolt pattern
St.x2.5
St.x1.5
steel fibres shotcrete and fully
Lattice girders
70/10/3
grouted rock bolts Φ25-S500s or
HEB
HEB140
standard swellex, also lattice girder
ribs. In areas with low overburden and poorer rock mass conditions as was the case in the portal
areas, ribs (HEB) were additionally used. The primary support of the tunnel was based on
shotcrete and bolt installation immediately after the round was blasted and muck removed.
3.2
Construction and monitoring
Left Branch
5.0
4.0
PS-D
4.5
3.0
PS-C
Advance Step
3.5
3.0
PS-B
2.0
2.5
2.0
1.5
Support category
4.0
PS-A
1.0
1.0
0.5
0.0
57.50
71.00
85.50
105.30
126.00
148.80
166.50
185.50
208.80
232.50
257.00
283.50
309.00
335.50
360.50
389.00
421.50
453.00
487.00
518.50
548.50
578.00
607.00
638.00
668.50
0.0
Chainage
Right Branch
4PS-D
4.5
4
Advance Step
3PS-C
3
2.5
2PS-B
2
1.5
1PS-A
1
0.5
0
0
Support Category
3.5
Construction of the tunnel started from the east
(entrance) portal. The first underground shift was on
27 May 2009 in the right bore and the left bore
followed shortly afterwards. By the end of January
2010, 630m had been excavated in each bore in a top
heading – bench sequence with an advance step that
varied from 1.5 to 4m. Figure 5 contains the data from
this time period, where the advance step of the top
heading is co-related to the support category that was
installed.
The excavation of the tunnel was smooth and did not
encounter any serious instability problems. The
original design for light support measures was fully
confirmed. Indeed, in view of the excellent rockmass,
when excavation of the other half of the tunnel - from
the exit to the middle – started, full-face excavation
was decided upon and performed.
51.00
65.00
83.50
103.50
124.00
143.00
161.70
183.70
207.80
234.80
257.60
282.60
310.60
336.60
362.50
392.00
425.50
456.50
488.50
520.00
547.00
576.50
606.00
636.00
662.00
During excavation in the initial stages it was found
that in areas where the sandstone intercalations were
of considerable thickness (~0.8-1.0) near the crown
over-excavations were formed (Fig.6). The location of
Fig. 5 Actual advance step and support
the over-excavations was consistent with structural
category of the east half top heading of the
instabilities evaluated during design. The blast hole
Kalydona tunnel
pattern was modified in order to reduce as much as
possible the overexcavations. The spacing of the
peripheral (contour) blast holes was reduced and the contour line closed in on the tunnel cross
section. This solution gave a better excavation profile and minor intrusions of rock were dealt with
mechanical scaling. It is of interest to mention that advance steps as long as 5m have been
Chainage
1st International Congress on Tunnels and Uunderground Structures in South-East Europe „USING UNDERGROUND SPACE“
April 7-9, 2011, Dubrovnik, Croatia
achieved with excellent profile and without any wedges detaching or overexcavations observed.
Most of the tunnel was excavated in such rock mass conditions with the rock mass ranging from
category A to category B.
According to the design, the tunnel construction was regularly monitored. More specifically, tunnel
convergence, bolt stresses and tunnel lining stresses were monitored. The instrumentation used
included convergence and geodetic stations with 5 monitor pins and deformation and stress-strain
stations, i.e. multiple point snap – ring anchor extensometers and five anchor hydraulic load cells.
In the case of tunnel portals area, NATM stress cells and strain gauges for steel ribs were also
used. A total of 57 convergence monitoring stations were installed but no more than a few
millimetres were ever measured.
4. Theoretical considerations
In order to explain the observed over-excavations, let us consider the slightly dipping Flysch layers,
with respect to the tunnel geometry. According to Goodman [6], rock with horizontal layering, tends to open up in the roof of
an underground opening. When the strata
are dipping, the zone of interbed separation
and potential buckling shifts off center and
the walls may be undermined by sliding, i.e.
in regularly layered rock, the stress flows
around the tunnel as if it had a shape different from that initially assumed. The extents
of these rock failure mechanisms depend,
among other things, on the friction between
the layers and the subsequent interlayer slip.
In the case of the relatively shallow Kalydona tunnel -consequently low stress enviFig. 6 Overexcavations at the crown
ronment- and additionally a high strength
over stress ratio, failure of the intact rock is
not expected. However, discontinuities may exert greater influence on the tunnel behaviour than
intact rock properties. The effect of the rock layers and the potential of slip amongst them, is examined as the possible cause for the observed over-excavations.
4.1
Fig. 7 Zones of layer slip around Kalydona tunnel using
Goodman’s geometrical method
Goodman’s geometrical method
Goodman [6] illustrated the effect of joint
slip by using a geometrical method to
examine the extent of slip along the
periphery of an underground opening. The
cross section of the opening and the friction
angle υj of the joint planes are the pieces of
information required to delimit the failure
mechanism. Zones of joint slip with potential
sliding and flexure around a tunnel of any
shape can easily be identified by drawing
two lines inclined at υj to the normal to the
layers and tangent to the tunnel periphery.
Figure 7 depicts this method for the
Kalydona tunnel driven in a rock mass with
one joint set dipping at an angle 5o from the
horizontal for joint friction angle equal to 30o.
1st International Congress on Tunnels and Uunderground Structures in South-East Europe „USING UNDERGROUND SPACE“
April 7-9, 2011, Dubrovnik, Croatia
The method offers a fast and precise estimation of the zones that may slip at the tunnel periphery
in the case of excavating in an anisotropic rock.
4.2
Analytical method
Daemen [7] developed a closed form solution to calculate the extent of the joint slip zones
through the elastic rockmass around circular tunnels
while Kumar [8] studied them for a Hoek-Brown
rockmass. According to Daemen the distribution of
elastic stresses, at first, is calculated. Then, the
elastic shear stress is compared to joint shear
strength, considering a Coulomb slip criterion for
the joint. The joint is considered to slip, when the
elastic shear stress τ exceeds the joint shear
strength τp. Therefore, slip zones identified by
Daemen correspond to excess shear stress contours
of τ/τp≥1. For a hydrostatic natural stress field the
orientation of the slip zones is determined by the
dip and friction angles of the weakness planes. For
an unsupported tunnel and for zero cohesion of the
joints the extent of the slip zone is also determined
by the joint friction angle. In cases of highly
anisotropic in situ stresses, tension zones may be
developed across existing weakness planes.
Fig. 8 Zones of layer slip around equivalent
Eventually, these zones strongly depend on the
Kalydona tunnel with analytical method
orientation of the weakness systems. The slip zones
calculated by the solution of Deamen according to
equation (1) for joint cohesion c=0 and υj=30o are shown in Figure 8 when zero support pressure
Ps is assumed. A circular unlined tunnel equivalent to the Kalydona tunnel cross-section has been
used as input.
r
R
2
P
Ps
S e cos 2 a
tan
j
Se c
P tan
j
sin 2 a
(1)
r, θ: polar coordinates
R: tunnel radius
P: Natural stress
Ps: support pressure
Se: factor of discontinuities shear overstressing (τ/τp), Se=1 in Figure 8
a: discontinuities inclination from horizontal
The existing analytic solutions do not take into account the redistribution of stresses around the
opening due to the joint slip. To further investigate any effect of such stress redistribution on
tunnel behaviour numerical analysis is needed.
4.3
Numerical investigations
The effect of the joint slip on the stress redistribution around a circular tunnel within a layered
rock mass has been examined numerically by Papavasiliou et al. [9] using the finite differences
code FLAC 2D. The ubiquitous joint model implemented in the FLAC code has been used,
assuming an elastic intact rock and planar joints having a Coulomb slip criterion with zero cohesion
and varying friction angle.
From these analyses it may be concluded that Goodman’s geometrical method presents very
precise results concerning the range of the slip zone around at the tunnel boundary. Further, the
closed–form solution of Daemen is confirmed to a reliable degree. However, for small or zero
values of the internal support pressure, the slip zoned predicted numerically may extend well
beyond the regions calculated analytically.
1st International Congress on Tunnels and Uunderground Structures in South-East Europe „USING UNDERGROUND SPACE“
April 7-9, 2011, Dubrovnik, Croatia
5. Numerical Analyses
5.1
Representation of anisotropy
Numerical simulation of the Kalydona tunnel is performed herein with the finite differences code
FLAC 2D v.6 (Itasca [10]). For the present analyses the ubiquitous joint model was selected as it
incorporates in the most comprehensive way the anisotropy of the flysch rockmass. In this model,
which accounts for the presence of an orientation of weakness in a Mohr-Coulomb model, yield
may occur in either the solid or along
the weak plane, or both, depending
on the stress state, the orientation of
the weak plane and the material
properties of the solid and weak plane.
In the numerical code implementation
(Itasca [10]), general failure is first
detected,
and
relevant
plastic
corrections are applied, as indicated in
the Mohr-Coulomb model. The new
stresses are then analyzed for failure
on the weak plane and updated
accordingly. The criterion for failure on
the plane consists in a local form of
the Mohr-Coulomb yield condition with
tension cut-off, the local shear flow
rule is non-associated and the local
tension flow rule, associated.
Figure 8 Numerical model discretization
The ubiquitous joint model may be
used to describe the mechanical behavior of a rock mass with one closely spaced joint set.
However, it does not account for the bedding rigidity of the rock layers. When this cannot be
neglected, other methods, such as the distinct element method -e.g. the UDEC code of Itasca- or
the cosserat continuum approach, e.g. Adhikary [11], may be more appropriate.
5.2
Numerical model
A plain strain model of 120m wide x 100m high with variable element size and stress boundary
conditions for the simulation of initial geostatic stresses has been used. Both tunnel tubes are
simulated in order to examine the possible interaction between them. A detailed numerical
simulation of tunnel excavation and support was
performed, based on the construction sequence
Table 4 Selected cross-sections for numerical models
suggested in the design. For the simulation of
the tunnel support, cable and beam elements
No
1
2
3
attached to the tunnel boundary, were used to
Chainage
24664.92
24465.41
24159.47
represent bolts and elastic shotcrete lining.
Branch
Right
Left
Right
Progressive hardening of the shotcrete was
taken into account. The internal stresses in the
Support
PS-A
PS-A
PS-C
lining developed at the final or any intermediate
Rockmass
A (II Sa)
B (II Si)
D (III Si)
excavation phase are due to the combined
Joint dip [o]
0
0
5
action of the elastoplastic rock response and the
joint slip. Figure 8 depicts the grid and structural
Overburden [m]
59
81
42
elements at the final excavation stage.
Monitored
1.9
2.7
5
Max ΓH [mm]
Calculated
Max ΓH [mm]
Three characteristic cross sections have been
selected for the simulations, with the prospect
of comparing the numerical results to actual
displacements. Geotechnical design parameters were selected according to the original tunnel
design (see Table 2). A zero joint cohesion was assumed while the joint friction was set to 35o, 33o
and 30o for rock mass IISa, IISi and IIISi respectively. Table 4 contains the details of the selected
cross-sections, the maximum vertical displacements that were observed at the crown after the top
1.61
3.01
4.65
1st International Congress on Tunnels and Uunderground Structures in South-East Europe „USING UNDERGROUND SPACE“
April 7-9, 2011, Dubrovnik, Croatia
Pin 2 10
ΔΗ
Dcl
8
6
4
2
Pin 1 10
8
6
4
2
0
-10 -8 -6 -4 -2
-2 0
-4
-6
-8
-10
0
-10 -8 -6 -4 -2 0
-2
ΔΗ
-4
Dcl
-6
-8
2
4
6
8 10
-10
2
4
6
8 10
10
8
6
4
2
0
-10 -8 -6 -4 -2
-2 0
-4
-6
-8
-10
ΔΗ
2
Dcl
Pin 3
4
6
8 10
Figure 9 Face mapping and geodetic monitoring at selected
cross-section No 1.
heading excavation and installation of
support and the respective vertical
displacements that were calculated
numerically using of the ubiquitous
joint model. It can be seen that there
is very good approximation of the
monitored displacements. In case (1)
of Table 4, the surrounding rock is the
best situation found along the tunnel,
undisturbed sandstone with RQD
values as high as 100. It is therefore
expected to have no monitored
displacements of the tunnel section. In
cases (2) and (3) though, there is
evidence of slight movement that is
well approximated numerically by the
ubiquitous joint numerical model. The
induced by excavation changes in local
stress magnitude and orientation are
in this case affecting joint slip
behaviour; the shear stress acting on
them exceeds the strength of the
weakness planes.
To this effect, a comparison of the
over-excavation profiles was possible,
by use of the face mappings of the
tunnel project. Figures 9 and 10
contain the visual comparison of face
mapping, measured convergence and
numerical results for the case of
analysis No1. The output from the
numerical solution is taken at the
stage where the excavation has just
been performed and installation of
support is underway. Colors represent
the element state and the areas of
Figure 10 Areas of slipped joints with use of ubiquitous joint model
joint slip are clearly coinciding with the
for Kalydona selected cross-section No 1.
over-excavation area in the face
mapping. It is of interest to note that
at the specific areas, redistribution of stresses after joint slip results in an elastic unloading and a
new equilibrium state (Ubiq. Jnts. Fail Past).
Similar results have been found for the cases (2) and (3) of Table 4, only the areas of slip are
more extensive. The maximum axial thrust in the temporary lining was calculated below 1 MN at
these areas, which is well within the applied shotcrete capacity.
Thanks to the appropriate design, side effects from interbedding slip did not spread. The support
measures that were applied were able to withstand the localized overstressing and the tunnel
excavation and primary support installation was completed successfully in mid-July of 2010.
6. Conclusions
Kalydona Tunnel, which is part of the currently under construction Ionia Motorway, has been
excavated with the drill and blast method in an undisturbed and of good mechanical properties
flysch formation. This allowed for light support measures, big round lengths and for one half of the
tunnel, full face excavation. In the tunnel periphery, at the shoulders, minor over-excavations
1st International Congress on Tunnels and Uunderground Structures in South-East Europe „USING UNDERGROUND SPACE“
April 7-9, 2011, Dubrovnik, Croatia
have been observed and been dealt with through an amelioration of the blast design according to
smooth blasting technics. The tunnel excavation has been successfully completed.
Analysis of excavation by considering the anisotropic nature of the flysch rockmass is performed by
using three different methods; geometrical, analytical and numerical. All methods provide a fair
estimate of the area of joint slip. In the case of the numerical method, application of the
ubiquitous joint model has been used with good results. Comparison of the numerical method
displacements to selected monitored tunnel cross-sections has yielded good agreement in
calculations as well as in joint slip behaviour.
7.
[1]
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]
[10]
[11]
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