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Analyisis of shallow tunnels construction in swelling grounds

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Swelling pressures of the rock as a result of chemical and physical processes which are present during construction and operation of tunnels and have the influence on loads and deformations of primary and inner concrete lining. Deep geomechanical analysis of swelling indicates that in practice very often conservative way of calculating load capacity of primary as well as inner lining were used with a goal to keep long-term stability of the tunnel. Particular emphasis was placed on the physical and chemical assessment of the time dependent development of deformation. In the present paper the practical case of tunnel construction in specific swelling clay ground »Sivica« is analyzed. Based on 2D and 3D geostatic analyses, a rigid primary lining was chosen as a final design, because the depth of the tunnel is only about 30 m below the surface. The geotechnical parameters of hoist ground »Sivica« are a result of laboratory and »in situ« tests, which were conducted according to technical standards. During a construction and after it the geotechnical measurements were conducted. The measurement results confirm the correct technical decision in the design stage.
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175
Jakob Likar1, *, Andrej Likar2, Jože Žarn1, Tina Marolt Čebašek1
1University of Ljubljana, Faculty of Natural Sciences and Engineering, Aškerčeva 12, 1000 Ljubljana, Slovenia
2Geoportal, d. o. o., Tehnološki park 21, 1000 Ljubljana, Slovenia
*Corresponding author. E-mail: jakob.likar@ntf.uni-lj.si
Received: August 4, 2015
Accepted: September 10, 2015
Original scientic paper
Abstract
Swelling pressures of the rock as a result of chemical
and physical processes which are present during con-
struction and operation of tunnels and have the influ-
ence on loads and deformations of primary and inner
concrete lining. Deep geomechanical analysis of swell-
ing indicates that in practice very often conservative
way of calculating load capacity of primary as well as
inner lining were used with a goal to keep long-term
stability of the tunnel. Particular emphasis was placed
on the physical and chemical assessment of the time
dependent development of deformation. In the present
paper the practical case of tunnel construction in spe-
cific swelling clay ground »Sivica« is analyzed. Based
on 2D and 3D geostatic analyses, a rigid primary lin-
ing was chosen as a final design, because the depth of
the tunnel is only about 30 m below the surface. The
geotechnical parameters of hoist ground »Sivica« are a
result of laboratory and »in situ« tests, which were con-
ducted according to technical standards. During a con-
struction and after it the geotechnical measurements
were conducted. The measurement results confirm the
correct technical decision in the design stage.
Key words: Road tunnel, support elements, Finite Ele-
ment Method, primary shotcrete lining, geotechnical
measurements
Izvleček
Nabrekalni tlaki v hribinah so rezultat kemijskih in
fizikalnih procesov, ki med gradnjo in obratovanjem
predorov vplivajo na obtežbe in deformacije, ki se raz-
vijajo tako v primarni kot tudi notranji betonski oblogi.
Poglobljene geomehanske analize nabrekalnih pojavov
v hribinah so pogosto osnova za konzervativne načine
izračuna potrebne nosilnosti primarne in tudi notranje
obloge predora z namenom, da se zagotovi dolgoroč-
na stabilnost podzemnega objekta. Posebna pozornost
analiz je namenjena fizikalnim in kemijskim procesom
v hribinah z nabrekalnim potencialom v odvisnosti od
časovno odvisnih deformacij. V tem prispevku je podan
praktičen primer gradnje cestnega predora v glinasti
hribini »Sivica«, ki ima specifične nabrekalne lastnosti.
Končna tehnična rešitev gradnje na osnovi rezultatov
geostatičnih analiz 2D in 3D je temeljila na uporabi toge
primarne obloge, ker je globina predora le okrog 30 m
pod površino terena. Geotehnični parametri »Sivice« so
bili določeni z upoštevanjem laboratorijskih in teren-
skih raziskav, ki so bile izvedene skladno z veljavnimi
standardi. Med gradnjo in po njej so bile izvajane ge-
otehnične meritve, katerih rezultati so omogočili pri-
merjavo z izračunanimi parametri in posledično potr-
ditev ustreznosti projektnih rešitev.
Ključne besede: cestni predor, metoda končnih ele-
mentov, primarna obloga iz brizganega betona, geoteh-
nične meritve
Analyisis of shallow tunnels construction
in swelling grounds
Analiza gradnje plitvih predorov v nabrekalnih
hribinah
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Introduction
Understanding the basic theory of chemical
and physical processes in swelling ground is
fundamental condition for successful technical
solution of tunnel construction in such circum-
stances. When tunneling takes place in swell-
ing ground such as anhydrite or swelling clay
minerals, i.e. montmorillonite, whole process
of construction, including underground water
presence and designed technology, needs to
be analyzed. This is very important, because
in the past in more cases of tunneling in such
grounds, after deep analysis were carried out,
clear shown the influence of unusable tech-
nology which caused and activated swelling
potential of present ground layers (Figure 1).
It is known that chemical reaction of anhydrite
(CaSO4) in the gypsum (CaS04 · 2H20) results in
the increase of volume up to 61 %. The similar
can apply in the shale formations with swell-
ing potential where physic-chemical reaction
depends on stress relief and reduction of the
chloride concentration by water adsorption
(osmotic swelling). The chloride ion diffusion is
assumed to be the mechanism for the reduction
of the chloride concentration.
Research activities of swelling
processes in ground
Numerous calculation methods have been
presented in the past to simulate the swell-
ing behavior and the resulting structural re-
sponse [1–9]. Very important laboratory tests on
swelling rocks were done by Barla [10], where
swelling gouge from weakness zone in tunnel
were investigated.
High sophisticated constitutive laws have been
developed to account for the phenomenon
of swelling in terms of continuum mechani-
cal models, i.e. [12–15]. Several PhD theses were
done on the topic of swelling processes in
rocks [10, 16, 17], in which authors were explained
fundamentals of physical and chemical base
of the such ground behavior. More attention is
paid on experimental investigation which was
done by [18]. He had shown the compression
and swelling behavior of the Callovo-Oxfordian
argillite. Two series of oedometric tests were
carried out, first one showed that the argillite
exhibits a swelling behavior even when fully
saturated under stresses higher than the in-si-
tu stress, and the second series of tests showed
that the swelling capacity appeared to increase
with compression. In both cases, swelling was
related either to pre-existing cracks due to
sample coring, storage, drying, wetting and
trimming or to cracks induced during compres-
sion. In this regard, compression was suspect-
ed to occur by local pore collapse that created
micro-cracks that afterwards swelled when hy-
drated. Indeed, sample compressed to a higher
pressure exhibited higher swelling potential.
A high quality investigation of swelling phe-
nomena was carried out [19] which focused on
repair works done in old railway tunnel in Swit-
zerland. Long-term laboratory tests showed
that the swelling behaviour occurred in stages
and bands of precipitated gypsum were found
in samples analysed by mineralogical test af-
ter test completion [20]. The swelling processes
require water and this could be facilitated by
spalling type fractures, brittle failure behaviour
with associated extensional fracture develop-
ment as a potentially controlling mechanism in
creating a water conductive zone beneath the
tunnel invert. Such brittle fractures were ob-
served during tunnel construction in anhydrite
by [21, 22]. Therefore, gypsum crystal growth is
most likely to occur where water has access
Figure 1: Typical events associated with swelling in tunnels according to [11].
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Analyisis of shallow tunnels construction in swelling grounds
177
and the state of stress is favourable for stress
fracturing. On the low confinement side of the
spalling limit, water has access through frac-
tured ground and the rock mass is essentially
free swelling until the support provides suffi-
cient pressure to prevent further swelling.
One of the important investigation of swelling
phenomena was relating to the goal of the pre-
sented investigations and that is to describe
the phenomenon of self-sealing quantitatively
(Figure 2, 3) and to establish a model, by means
of which it is possible to take the self-sealing
phenomenon into account when designing tun-
nels in swelling rock [23, 24].
It is expected, that due to the new models a
more effective and economic design of tun-
nels in swelling rock will be possible. Swelling
pressures, which had been identified in some
old railway tunnels that were built in the 19th
and in the early years of the 20th century, man-
ifested in many cases, particularly in the floor
inverts. In some cases it was necessary to car-
ry out rehabilitation even twice, because the
invert had shallow arch which hadn’t enough
Figure 2: Mechanisms of self-sealing in SBR [23].
Figure 3: Characteristics of tests sections in test gallery U1 of Freudenstein tunnel modified [25].
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static resistance of the support ring (Wagen-
burgtunnel, built in 1957) [26]. From several
analyzed cases it can be summarized that the
process of swelling is usually intensely present
in the floor and in the sides of the underground
facility, which represents lower static capacity
of the structure.
Special case of tunnel construction in swelling
rocks was Engelbergtunnel tunnel, which was
built in 1990 [26]. The primary lining has been
damaged at the beginning of construction at
the connection point between the tunnel side
the tunnel invert. At the beginning the original
basic design was based on dry rock conditions
during construction. Furthermore, in the upper
design stage it was planned inner lining of re-
inforced concrete in the goal to excluding the
effect of swelling pressure of the surrounding
rock. During the construction phase, the design
concept was significantly revised since instead
of 30 cm thick shotcrete lining in the invert,
1.5 m thick concrete lining was installed, ad-
ditionally anchored in the foundation ground.
This way sufficient static resistance to swelling
pressures was provided. Above anchored and
reinforced invert high deformable layer called
»Knautschzone« was constructed to prevent
possible damages on the inner lining. And final-
ly, the inner lining in invert was installed with a
thickness of 3 m, as shown in Figure 4.
In the design procedure is important question
when in case of construction of the under-
ground facility the increment of the volume
change will be prevented enough with the in-
stallation of rigid support system in the goal
to reduced deformation in acceptable limit.
That requirement in the conclusion still need
adequate primary lining with sufficient load
bearing capacity to ensure stability during the
construction. It should be noted that the time
evolution of swelling pressures depends on
the amount of water in contact with swelling
ground and stiffness properties of the prima-
ry lining. This takes into account the principle
of long-term stability of the facility with the
primary lining, which consists of a standard
shotcrete lining, steel arches, steel wire mesh
and rock bolts or anchors. A typical example
of the combination of swelling and squeezing
rocks can be found in Karavanke road tunnel
connecting Slovenia and Austria, which was
built in the second half of the 1980s and put in
operation in 1991. In fact is that deformations,
which in some sections had started to develop
immediately after completion of construction
or even already in the time of construction did
not stabilize. The continuous time developed
deformations called for the implementation of
the rehabilitation of certain sections. Measure-
ments which were carried out in the last years
showed that the deformation process after re-
furbishment not stopped in some sections. Due
to difficulties in identifying key parameters for
such swelling laws the engineering approach
predicting the swelling pressure used back-cal-
culation of data monitored during construction
of the tunnel in similar ground conditions. The
last investigations in the Karavanke tunnel have
shown that installation of a deformable layer in
the invert between surroundings rocks and re-
furbished primary lining can be right technical
solution for time stable tunnel structure.
Figure 4: Construction the Engelbergtunnel [23].
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Analyisis of shallow tunnels construction in swelling grounds
179
Basic principles of support system
design in swelling ground
The primary mode of support system planning
is based on the principle of ensuring a balance
between swelling capacity of ground and react-
ing support pressure. It is exposed to the vol-
ume increase that occurs after the excavation
step. The relationship swelling ground - sup-
port system has important influence on the
location of the equilibrium system, as shown
in the Figure5. It should be noted that the re-
lease of ground strain is a result of mobilization
bearing capacity of the ground and at the same
time swelling forces are generated when water
or air moisture find the contact with ground
surface at the excavation round in the tunnel.
Quick and effective prevention of water access
indirectly reduces formation of higher swelling
pressures relating to formation efficient activa-
tion of the self-protection ground layer around
tunnel wall. Exactly that self-protective effect
has a unique role on reaching equilibrium be-
tween the supports system and surrounding
ground.
Swelling phenomena aplication in
the tunnel Ljubno design
The presented case of the shallow tunnel Ljub-
no with maximum overburden of about 30 m
was built in the ground with swelling potential
in the northern part of motorway section A2
Karavanke (Austria) – Obrežje (Croatia), and
has shown specific circumstances relating to
geotechnical conditions assessment.
The new Tunnel Ljubno was built as the twine
road tunnel including reconstruction of the old
tunnel tube which is now a part of new motor-
way (Figure 6). The old tunnel tube was con-
structed in the 60s of the past century without
invert (Figure 6). In more than 40 years that
the tunnel was in operation damages such as
lifting of the pavement similar as shown in
Figure 1–a) occurred. Reconstruction of the old
tunnel tube included extension of the current
clearance profile according to the standard
that requires two lanes with a width of 3.75 m,
one intervention lane with a width of 3.20 m
and two intervention corridors with a width of
0.8 m which is the same as in the new tunnel
which was built 40 m away. The amount of ex-
cavated material in the profile is approximately
86 m2 per running meter of the tunnel.
Results of geological and geotechnical
investigation
In order to design construction and recon-
struction of tunnel tubes extensive field and
laboratory investigations and explorations
Figure 5: Basic principle of tunnel support design in swelling
ground.
Figure 6: Location of the new and old tunnel tube with
maximum overburden of about 30 m and clearance profiles of
the old tunnel before reconstruction and after it.
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were carried out to determine geological and
geotechnical characteristic of ground materials
present in the tunnel area. All investigations
and geostatic analysis were carried out be-
fore the design of new tunnel tube which was
constructed first before the reconstruction of
old tunnel tube begun. Special attention was
paid to the investigation of hard clay known
as »Sivica« in which majority of the excavation
works were done. Design of excavation and
primary support lining was done in an appro-
priate way due to extensive amount of informa-
tion acquired by geological mapping, boreholes
drilling, Standard Penetration Tests and Pres-
suremeter Tests. The prognosis of geological
structure is shown on the longitudinal profile
in Figure 7. Distance between tunnel tubes is
shown in the Figure 8.
The laboratory tests included measurements of
moisture content, UCS, Triaxial Shear Tests and
particularly attention was paid to the measure-
ments of swelling potential and deformability of
»Sivica«. It was found that in a dry environment
»Sivica« has solid strength properties, while
contact with water causes the relatively high
presence of swelling potential. A large number
Type
of ground
Moisture
w/%
Unit
weight
γ/
(kN/m3)
Youg
Modulus
E/MPa
Poisson
ratio
ν
Tensile
strenght
σt/MPa
Unconfined
compresive
strenght
σc/MPa
Angle of
internal
friction
φ
Cohesion
c/MPa
Silty clay 25.0 20.0 5.0 0.4 / 0.001 25.0 0.0
Conglomerat / 25.0 4 000.0 0.2 / / 40.0 0.5
»Sivica« 7.0 24.0 200.0 0.3 0.5 5.0 31.0 0.136
Weathered
»Sivica« / 20.0 4.0 0.4 / / 23.0 0.0
Table 1: Basic geotechnical parameters of the existing ground layers
Figure 7: Longitudinal geological profile of the new tunnel tube.
Table 2: Laboratory determined sweling pressure at prevented strains and swelling strains in the unloading stress conditions
Depth below the
ground (m)
(»Sivica«)
Primary vertical
ground pressure
σv/MPa
Swelling pressure
psw/MPa at total
prevented strains
Swelling strain εsw/% at
water presece at total first
unloading/second
unloading conditions
25.0 0.600 0.250 2.0/3.5
20.0 0.480 0.350 2.0/4.0
16.0 0.385 1.45 1.8 /2.0
33.0 0.800 ≥ 1.5 1.3/4.0
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Analyisis of shallow tunnels construction in swelling grounds
181
of laboratory tests to describe rock properties
including swelling had been performed. The re-
sults were represented in Table 1 and Table 2.
One of the most important investigations was
XRD Analysis which was carried out with the
goal to determine the mineralogical content of
the »Sivica« sediment samples. The diffraction
patterns were identified with the data from
X’Pert HighScore Plus software ICDD database.
The compact gray clay samples were analysed
with handheld XRF analyser NI TON GOLDD+
model XL3t He (50 kV) for major and minor
element concentrations. The XRF result rep-
resents average of four measurements. Analy-
ses were run with helium purge in the XRF in
order to determine the degree of improvement
in the signal detection attributable to helium’s
elimination of scattering by atmospheric gases.
The analyser uses a 50 keV miniaturized X-ray
tube and can quantify elements from magne-
sium through uranium. Data for all experiments
consisted of counts (of X-ray fluorescence) de-
tected per second. Total acquisition times were
kept constant at 180 s. Bal variable is balance
and incorporates all light elements from H to
Na that cannot be detected with this XRF anal-
yser.
Based on given results as shown on Figure 10
the conclusion has shown that fresh clay sam-
ple does not contain any swelling minerals. The
clinochlore (chlorite) in the clay sample does
not change volume upon solvation with eth-
ylene glycol, but only with the addition of water.
When the chlorite mineral in the clay is altered
by surface weathering, the alteration in the
slate appears to be relatively rapid and com-
plete. Direct surface exposure of the clay leads
to the apparent irreversible dehydration of the
surface layer of the clay. Weathering procedure
is the manner in which chlorite ordinary alters
when subjected to an atmospheric environ-
ment. It seems that alteration of chlorite leads
to formation of mixed-layer chlorite-vermic-
ulite and possibly to montmorillonite (Mg-sa-
ponite) which are well known swelling clay
minerals.
From the results revealed the presence of
swelling potential (Figure 9) and investigation
based on XRF analyser (Figure 10), it cannot
clear demonstrate the unique possibilities of
activation swelling process during construction
or reconstruction the tunnel tubes. Taking into
account all results of swelling potential analy-
sis, back geotechnical analysis of stability the
old tunnel tube (Figure 5) and considerations
in the mentioned scientific founding published
in adequate journals in the deeper geotech-
nical design analysis used swelling pressure
psw = 1 200 kPa.
Figure 8: Vertical cross section through existing (right) and
new tunnel tube (left) with low overburden.
Figure 9: Laboratory test results of swelling potential of the
dark grey hart clay »Sivica« on the sample from the depth
33.0–33.3 m below the ground surface which is close to
tunnel tubes locations.
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Designed solution for tunnel construction
and reconstruction
Due to the expected behaviour of »Sivica« the
design provided technological measures to
reduce the danger of water influence on the
strength of the intact geological material. Im-
mediately after excavation free surface was
protected with shotcrete. Drilling and anchor-
ing techniques without water usage were im-
plemented. The purpose of these measures was
to avoid contact between ground and any type
of water and thus keep »Sivica« in its natural
conditions. The basis for determining the swell-
ing ground - support system relationship is a
relation between the reactive support pressure
and the tunnel wall deformations, as shown in
the Figure 11 which is prepared on the basis of
assessment usable swelling pressure including
in accounting the stiffness of primary shotcrete
lining. For assessment of relevant value of de-
sign swelling pressure, the elastic pre-defor-
mations εui = 0.4 % and stiffness of shotcrete
primary lining kc = 540 MPa with adequate
εsw = 0.3 % radial strains were used in the equa-
tions based on close form solution method. The
geostatic primary vertical pressure in the rock
and the additional swelling pressure which was
obtained from laboratory tests (Table 2) were
included in the geostatic calculations.
The reduction of reaction support pressure was
achieved by introducing the flexibility of the pri-
mary support system. Reserves in the capacity
of proposed support system were established
with a safety factor against the collapse. That
was applied during the calculation of internal
forces and bending moments from the results
of 3D geostatic analyses which are described in
the next subsection. Determination of the size
of the damaged zone around the tunnel lining
in the old tunnel tube was determined based on
the examination of drilling cores, which have
been acquired in the research stage of design.
Figure 10: Result of XRF analysis.
Figure 11: Designed support measures for essential length of tunnel.
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Analyisis of shallow tunnels construction in swelling grounds
183
This ranged from 0.5 m to the on the tunnel
roof and around 1.0 m on the tunnel sides and
in the floor without invert. During the recon-
struction of the old tunnel tubes (Figure 13)
the damaged layer around the old tunnel was
removed, which is favourable for the establish-
ment of long-term geostatic stability the tunnel
system (Figure 12).
Based on the analysis of different theoretical
approaches and practical cases of tunnel con-
struction in swelling grounds including the
geometrical data and thickness of ground lay-
ers cover, the rigid support system was applied.
To follow this goal, the standard supporting
elements have been considered in the design
such as steel arches K24 and sprayed cement
concrete thickness between 30 cm and 35 cm
with two layers of wire meshes and rock bolts
if required (Figure 11). The whole length of the
tunnel tubes was scheduled with invert built
from shotcrete with the same thickness. Rock
classification was made according to Austrian
standards OENORM B 2203.
Geostatic analysis of tunnels support
measures
To verify the support measures designed as pri-
mary lining, extensive 2D and 3D numeric anal-
yses, using Phase2D and MIDAS GTS computers
codes, were done. The comparison between
load cases without and with considering addi-
tional pressures caused by swelling (340 kPa)
were carried out for two different design solu-
tions. The swelling pressure was simulated with
proportionally higher unit weight of ground. In
the Table 3 and Table 4 input ground geotech-
nical data for both numeric analyses are shown.
The excavation of the tunnel was divided into
a top heading, bench and invert, while on the
longitudinal direction the excavation was simu-
lated in progressive steps of 2 m in length.
The support elements in the calculations were
planned with reinforced shotcrete lining with
two steel meshes. Figures 14 and 15 shows the
results of the calculation displacements with-
out and with swelling pressure considered. In
the first case the displacement could reach the
value of 3.0 cm in the invert and, while in the
second case, displacements were below 6.5 cm.
The values of displacement for both calcula-
tions are shown in the Table 5. From the same
figures the area of influence of tunnel excava-
tion is in the worst case stretched up to 15 m
left and right of the planed axis of the new tun-
nel, which means that the new tunnel tube ex-
cavation on the existing tunnel tube practically
hasn’t effect on stress-strain changes. The same
can be concluded from the Figures 16 and 17,
where the calculated Strength Factor (SF) is
shown. If the values and distribution of main
stresses Sigma 1 and Sigma 3, FS and total dis-
placements around tunnel tubes are compared
with each other, it is evident that the main con-
centration are present in the invert area.
This is mostly related to shallow depth of the
tunnel locations and stiff static resistivity of
primary linings incorporated in the low bear-
ing capacity of surrounding ground.
3D FEM analysis were carried out in the simi-
lar way as 2D calculations. The first numerical
simulation was done when the excavation pro-
cedure of the new tunnel tube was analyzed.
Calculated total diplacement which are shown
in Figure 18 has the maximum value approx.
8.5 cm in the invert and the minimum value
approx. 3.0 cm on the crown. In the next short
presentations of calculations results we can
find that higher stresses and strains in the pri-
mary lining existed in the roof and invert parts
of tunnels tubes (Figure 19 and 20). That are
comparable with results of 2D analysis which
were shown in Figure 14 to 17.
Figure 12: Reactive support pressure versus radial strain in
the swelling ground.
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Figure 13: Designed reconstruction procedure for old tunnel tube.
Type of
ground
Unit weight
γ/(kN/m3)
Young
Modulus
E/MPa
Poisson
ratio
ν
Cohesion
c/kPa
Angle of
internal
friction φ
Silt 20 5 0.4 1.0 25
Conglomerat 25 4 000 0.2 500.0 40
Sivica 24 200 0.3 136.0 31
Table 3: Input geotechnical ground data for the analysis
Table 4: Mechanical parameters of support elements
Support
element
Unit weight
γ/(kN/m3)
Young
Modulus
E/MPa
Poisson
ratio
ν
Thick of
primary
lining (m)
Wire mesh
Q189
(pcs.)
Shotcrete (fresh) 25 3 000 0.30 0.35 2
Shotcrete (final) 25 15 000 0.25 0.35 2
Object
Calculated maximum displacements (cm)
without swelling with swelling
invert side wall invert side wall
New tunnel tube 3.0 1.1 6.2 2.3
Reconstructed tunnel tube 1.1 0.7 1.4 1.0
Table 5: Calculated displacements in the invert and side walls
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185
The results of 3D simulations of the excavation
and primary support installation for new and
reshaped tunnel tube with respect to the swell-
ing pressure of the surrounding rock are calcu-
lated depending on the depth and characteris-
tics of »Sivica« and the size of the tunnel tubes.
For both tunnel tubes calculated total displace-
ments are between 2 cm and 6 cm at the roof
and invert (Figure 21).
Figure 15: Calculated displacements in the new and reconstructed tunnel tube with taking into account designed swelling
pressure.
Figure 16: Calculated Strength Factor (SF) in the ground for the new and reconstructed tunnel tube without taking into account
designed swelling pressure.
Figure 14: Calculated displacements in the new and reconstructed tunnel tube without taking into account designed swelling
pressure.
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The maximum axial forces in the primary lin-
ing were found in the both sides where the
calculated values are around –5 000 kN. While
the smallest values of calculation results are
shown in the roof and in the invert of tunnel
tubes which amount to around –300 kN. It is
worth noting, as their value is very small and
is close to the tension zone, which is which is
compensated by a double reinforcement wire
mesh, so that provides sufficient safety against
Figure 17: Calculated Strength Factor (SF) in the ground for the new and reconstructed tunnel tube with taking into account
designed swelling pressure.
Figure 18: Total displacements after excavation and support of the new tunnel (left tube direction toward Ljubljana).
Figure 19: Tangential axial forces in primary lining – new
tunnel (left tube).
Figure 20: Bending moments in primary lining – left tube.
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Analyisis of shallow tunnels construction in swelling grounds
187
the development of tensile cracks. Particular
attention was dedicated to the construction
of joint primary lining in contact between top
heading and bench with invert. The results are
shown in Figure 22. Analysis of the bending
moments in the primary support shows that
in the ceiling value regardless of the format of
a positive in ground vault but negative. Their
value ranges from about +82 kN m/m to about
–122 kN m/m, which is not a problem for the
provision of required stability (Figure 23).
Some distinctive features of the construction
A relatively short length of the tunnel was not
suited for performing excavation with sever-
al phases going on simultaneously. Therefore,
the excavation of the concrete invert was made
first, followed by making a bench and top head-
ing which were constructed together. Since the
northern portal was not accessible, the whole
excavation was made from the southern portal
running towards the northern portal, where the
breakthrough was made directly to the surface,
meaning that no previous protective measures
were necessary on the northern portal.
Figure 24 shows the breakthrough of the top
heading in the inaccessible area. The last few
metres of the top heading were built in the side
gallery, with the cross section profile of approx.
one third of the cross section of the top heading.
This method of excavation reduced the risk of
overbreak during the breakthrough. The break-
through, as well as the excavation of northern
portal and excavation of the remaining top
heading of the tunnel, were made successively.
Figure 21: Total displacements after excavation and support of the right tube (direction toward Ljubljana).
Figure 22: Tangential axial forces in primary lining – left and
right tube after excavation and support of the old one tunnel
(right tube – direction toward Ljubljana).
Figure 23: Bending moments in primary lining – left and
right tube after excavation and support of the right tube.
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RMZ M&G | 2015 | Vol. 62 | pp. 175–191
Figure 24: Excavation face and
breakthrough at the Nord portal
of the new tunnel tube and
reconstruction of the old tunnel.
Figure 25: Measurement results
of additional circular and radial
stresses in the contact between
ground and primary lining in the
new tunnel tube.
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Analyisis of shallow tunnels construction in swelling grounds
189
Gelogical observations and geotechnical
measurement during construction and in
operation
The results of monitoring measurements in
pressure cells (and extensometers), which
were installed during the construction of the
new tunnel tube in the same geological geo-
technical conditions did not show additional
increases in circular (tangential) and radial
stress (Figure 25 and 26) as a result of influ-
ence of the reconstruction of old tunnel.
In future the swelling potential will not produce
additional stresses on the inner lining, because
the primary lining has a sufficient loading ca-
pacity. The process which explains swelling
pressure increase in examined ground shows
that the closure of cracks depends of ground
water isolation.
This is consistent with the results of extensive
research of various swelling rock types [25, 26],
which have rheological properties similar to
hard clay (Sivica). It has been proven that nat-
urally developed swelling pressures are much
lower or minimum than those which are ob-
tained from laboratory investigations. The de-
termination of meaningful swelling pressure to
be applied to the tunnel lining based on labora-
tory tests is largely depending on the scale ef-
fect, the stiffness ratio of the tunnel lining and
surrounding ground and the in-situ stress and
water conditions. Hence, swelling load condi-
tions are difficult to predict in the reality. The
displacements measured during the excavation
were smaller than expected, i.e. less than 3 cm.
This is probably due to more favourable geolog-
ical and geotechnical conditions and high level
of technological discipline of contractor. Mea-
surements of displacements over time proved
that the process slowed down and practically
stopped one week after the excavation, with-
Figure 26:
Measurement results of
additional circular and
radial stresses in the
contact between ground
and primary lining in
the reconstructed tunnel
tube.
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RMZ M&G | 2015 | Vol. 62 | pp. 175–191
out any significant deviations. The excavation
of the bench was followed by the excavation of
the concrete invert and building of the founda-
tions and concrete invert, at a suitable distance
of about 30 m to 40 m.
During the excavation of the new tunnel tube,
displacements of the lining in the adjacent ex-
isting tunnel tube have been monitored. Only
minimal displacements have been noticed,
mainly caused by vibrations and due to precise
measurements and inaccessibility of the mea-
suring points. The results of measurements
have shown that the construction of the new
tunnel tube has no impact on the existing tun-
nel.
Conclusions
In recent decades many studies were conduct-
ed relating to investigation of the construction
of tunnels in the swelling rocks. The main goal
of these investigations was determination the
effects of chemical and physical processes on
the swelling pressure development with time.
The essential distinction in the design of tun-
nels in the swelling grounds is depth i.e. pri-
mary stress state in grounds layer and other
geological and geomechanical properties of
geological materials.
Different approaches to research, interpreta-
tion of their results and suggesting methods of
tunnel construction in these types of grounds
are a good basis for the construction method
decision for each case separately.
Substantial progress in understanding the de-
velopment of swelling pressure is taken into ac-
count self- closure effect. This is important for
the proper selection of construction technolo-
gies which should be at the time of construc-
tion imposed to strict control.
Successfully design and build a new tunnel
tube and reconstruction of an old tunnel tube
of the road tunnel Ljubno in the dark gray clay
»Sivica« with swelling potential, is an example
of good engineering practice in the construc-
tion of shallow tunnels in swelling rocks.
References
[1] Einstein, H. H., Bischoff, N. (1975): Design of Tunnels
in Swelling Rocks. 16th Symposium on Rock Me-
chanics; University of Minnesota, Minneapolis, MN,
pp. 185–195
[2] Einstein, H. H. (1996): Tunnelling in difficult ground
– Swelling behaviour and identification of swelling
rocks. Rock mechanics and rock engineering; 29 (3),
pp. 13–124.
[3] Gysel, M., (1987): Design of tunnels in swelling rock.
Rock Mech. Rock Eng.; 20 (4), pp. 219–242.
[4] Kovari, K, Amstad, C, Anagnostou, G (1988). Design/
construction methods - Tunnelling in swelling rocks.
In: Cundall et al. (eds) Key Questions in Rock Me-
chanics: The 29th US Symposium on Rock Mechanics
Balkema, Rotterdam, pp. 17–31.
[5] Lombardi, G. (1984): Underground openings in
swelling rock. Proc. 1st Nat. Conf. on Case Histories in
Geotechnical Engineering. Lahore, Pakistan.
[6] ISRM (1983): Characterisation of Swelling Rock.
Commission on Swelling Rock. Pergamon Press.
Oxford, U.K.
[7] ISRM (1989): Suggested methods for laboratory
testing of argillaceous swelling rocks. Commission
on Swelling Rock. Co-ordinator: H. Einstein. Int.
J. Rock Mech. Min. Sci. & Goemech. Abstr.; 26 (5),
pp. 415–426.
[8] ISRM (1994a): Comments and recommendations
on design and analysis procedures for structures in
argillaceous swelling rock. Commission on Swelling
Rock. Co-ordinator: H. Einstein. Int. J. Rock Mech. and
Sci. & Geomech. Abstr.; 36, pp. 293–306.
[9] ISRM (1994b). Suggested methods for rapid field
identification of swelling and slaking rocks. Com-
mission on Swelling Rock. Co-ordinator: H. Einstein.
Int. J. Rock Mech. and Min. Sci. & Geomech. Abstr.; 31,
pp. 545–548.
[10] Barla, M. (1999): Tunnels in Swelling Ground –
Simulation of 3D Stress Paths by Triaxial Laboratory
Testing. Ph. D. Thesis. Politecnico di Torino.
[11] Amstad, C., Kovári, K., (2001): Untertagbau in quell-
fähigem Fels, Forschungsbericht 52/94, Bundesamt
für Strassen (ASTRA) Bern.
[12] Grunicke, U., Walter W. and Hofstetter G. (2002):
Design of Tunnels in Swelling Rock, Felsbau; 20 (6),
pp. 25–34.
[13] Anagnostou, G. (2007): Zur Problematik des Tunnel-
baus in quellfähigem Gebirge, Mitteilungen der Sch-
weiz. Ges. für Boden- und Felsmechanik, Band 154.
ACCEPTED
Analyisis of shallow tunnels construction in swelling grounds
191
[14] Heidkamp, H., Katz, C. (2004): The swelling phenom-
enon of soils - Proposal of an efficient continuum
modelling approach, EUROCK 2004 & 53rd Geome-
chanics Colloquium.
[15] Wittke-Gattermann, P. and Wittke, M. (2004): Compu-
tation of Strains and Pressures for Tunnels in Swelling
Rocks. ITA-AITES congress, pp. E14 1–8.
[16] Bellwald, P. (1990): A contribution to the design of
tunnels in argillaceous rock. Ph.D. Thesis. Massachu-
setts Institute of technology, Boston, USA.
[17] Aristorenas, G. V. (1989): Rheological modelling
of swelling rocks. Internal report, Massachusetts
Institute of Technology. Boston, USA. Unpublished,
included as Chap. 2 in Aristorenas 1992.
[18] M. Mohajerani et al. (2011): Oedometric compres-
sion and swelling behaviour of the Callovo-Oxfordian
argillite. International Journal of Rock Mechanics and
Mining Sciences; 48 (4), pp. 606–615.
[19] Steiner, W. (1993): Swelling rock in tunnels: Charac-
terization, effect of horizontal stresses and Con-
struction Procedures. Int. J. of Rock Mech.s and Min.
Sciences & Geomech. Abstracts; 30 (4), pp. 361–380.
[20] Nüesch, R., Steiner, W., Madsen, F. (1995): Long
time swelling of anhydritic rock, mineralogical and
micro-structural evaluation, Proc. 8th Int. Conference
on Rock Mech., Tokyo, Japan, pp. 133–138.
[21] Grob, H. (1972): Schwelldruck im Belchentunnel.
Int. Symposium für Untertagebau, Luzern, Schweiz,
pp. 99–119.
[22] Spaun, G. (1974): Über die Ursachen von Sohlhebun-
gen in Tunneln der Gipskeupers. Festschrift Leopold
Müller-Salzburg zum 65. Geburtstag, Karlsruhe, pp.
245–260.
[23] Wittke, M. (2003): Begrenzung der Quelldriicke durch
Selbstabdichtung beim Tunnelbau im anhydritfiihren-
den Gebirge. WBI Print 13.2 vols. Gluckauf. 112.
[24] Wittke, W. (2007): New high-speed railway lines
Stuttgart 21 and Wendlingen-Ulm - Approximately
100 km of tunnels, in Underground Space. – The
4th Dimension of Metropolises, Proceedings of the
World Tunnel Congress 2007 and 33rd ITA/AITES
Annual General Assembly, Prague, May 2007, edited
by J. Bartak, I. Hrdina, G. Romancov, and J. Zlamal,
pp. 771–778, Taylor & Francis, London, UK.
[25] Wittke, W. (2000): Swelling Stability Analysis for
Tunnels – Fundamentals. Verlag Glu¨ckauf GmbH,
Essen, Germany.
[26] Wittke, M. (2002): Design of tunnels in swelling rock,
Porc. NUMGE 2002, 5th European Conference on
Numerical Methods in Geotechnical Engineering.
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The Callovo-Oxfordian (COx) argillite is a possible host rock for radioactive waste disposal in which the ANDRA underground laboratory of Bure (East of France) has been excavated. In this paper some aspects of the volume change behaviour of the COx argillite are investigated. To do so, high pressure oedometers with a maximum capacity of 113 MPa have been used. In a first stage, swelling tests were carried out on samples initially compressed at constant initial water content (unsaturated) that were afterwards soaked under vertical loads, respectively, smaller and higher than the in-situ vertical stress. All samples exhibited swelling, even at stress higher than the in-situ stress. In a second stage, standard step-loading compression tests were carried out on samples previously saturated under the in-situ vertical load, so as to investigate the volume change behaviour under load cycles. The strain–stress curves obtained appear to be different to what is currently observed in overconsolidated or cemented clays, with no clear appearance of yield and pre-yield reversible behaviour. The volumetric behaviour during both compaction and swelling is interpreted in terms of damage created by the collapse of pores within a fragile matrix. The amount of swelling observed is related to the extent of damage.
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Tunnels through shales, marls and anhydritic shales experience swelling phenomena. Case histories have been reviewed. Swelling pressures from laboratory tests and associated in situ observations of swelling pressures have been reviewed. Effects of construction procedures and the influence of horizontal and lateral stresses have been studied. For shales it was found that laboratory swelling pressures appear to be much higher, often by an order of magnitude than in situ values. The in situ values are below 1 MPa, many cases indicate only 0.3 M Pa or less. In anhydritic shale, where a chemical component influences swelling behaviour, swelling pressures in the range of 2–2.5 M Pa have been observed in situ. Laboratory values are usually much higher. Horizontal and lateral stresses play a major role both in laboratory and in situ tests. For in situ stresses from overconsolidation, experience from clay soil has been extrapolated to mesozoic sedimentary rock and calibrated on in situ measurements. Horizontal and lateral stresses must be explicitly considered in swelling rocks, as well as pore-water pressures. Recommendations on improvement of laboratory tests are given.
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For the large scale projects new high-speed railway line (NBS) Wendlingen-Ulm and Stuttgart 21, a total of approx. 100 km long single- and to a small extent also double-track tunnel tubes are foreseen. In the course of the NBS Wendlingen-Ulm, among other structures, the 8.7 km long Boßlertunnel and the 4.7 km long Steinbühltunnel are planned. The Boßlertunnel is located in Brown Jurassic. Locally, squeezing rock is to be expected. The Steinbühltunnel is located in White Jurassic, which is locally strongly karstified. For both tunnels, it was investigated whether an advancing test section and through-going exploratory adits respectively would lead to a safer design with regard to construction costs and time. A total of approx. 52 km single- and double-track tunnel tubes is foreseen for the project Stuttgart 21. The paper exemplary illustrates the Fildertunnel. With regard to tunneling, the tunnel sections in swelling unleached Gypsum Keuper are of major importance. The principle of resisting support is planned to be carried out.
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A three dimensional constitutive law for swelling rock is presented. It can be applied to the osmotic swelling of mudstone as well as to the swelling of rocks containing anhydrite. It describes the development of time-dependent strains and stresses due to swelling considering elastic and viscoplastic behaviour. Furthermore the anisotropic swelling behaviour is considered. This constitutive model was implemented within a numerical computation program according to the finite element method and calibrated with the aid of back-analyses of monitoring results in the exploration gallery of the Freudenstein tunnel which is completely located in the unleached Gypsum Keuper. A good agreement between numerical solutions and monitoring results could be achieved. Finally an outlook on a new design concept considering self-sealing effects around tunnels in anhydritic rocks is given.
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Design and construction of tunnels in swelling rock may be considered to be a matter of choosing the right tunnel cross-sectional form and the appropriate excavation methods and sequences. Experience, i. e. empirical knowledge, no doubt plays a fundamental role in tunnelling and even more so in tunnelling in swelling rock formations. However, the design engineer needs some tools to analyze the forces which are transmitted from the swelling rock to the tunnel lining in a given case. These tools may provide approximations of the real behavior. However, approximate quantitative indications are very valuable in order to supplement the mentioned empirical knowledge. The analysis method given in the paper is meant to provide such a tool for circular tunnels in swelling rock of the reversible type (swelling of clay minerals). The main approximation of the method is the consequent use of the theory of elasticity as framework for the specific swelling calculations. Since the widely used oedometer swelling test until now is also interpreted using the theory of elasticity, the analysis method is compatible with the kind of assessment of the swelling parameters. The main advantage of the method, however, is its relative simplicity because it may be used quite similarly to the method of “characteristic lines”. In principle, the method could be transformed into an elasto-plastic approach. As long as the greatest uncertainty of the design methods, however, lies in the right choice of the swelling parameters, a too complicated analysis method is hardly beneficial. For complex cases, where the geometrical boundary conditions may not allow the use of a circular tunnel model, it is advisable to use finite element solutions which are available for swelling calculations in the elasto-plastic formulation straight away.
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This brief review first describes typical swelling phenomena in underground openings and then discusses in detail the underlying swelling mechanisms. Mechanical, osmotic and intracrystalline swelling in argillaceous ground, as well as hydration of anhydrite are described. The fact that many of these mechanisms interact and, particularly, that swelling and squeezing may occur simultaneously is emphasized. The paper concludes with a few comments on implications on analysis, design and construction.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Civil Engineering, 1992. Includes bibliographical references (leaves 263-269).
Underground openings in swelling rock
  • G Lombardi
Lombardi, G. (1984): Underground openings in swelling rock. Proc. 1st Nat. Conf. on Case Histories in Geotechnical Engineering. Lahore, Pakistan.