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DESIGN OF THE TECHNOLOGICAL PROCEDURE OF BUILDING
THE DRIVEN TUNNEL BY MEANS OF PHYSICAL MODELLING
Weiglová Kamila
Brno University of Technology, Faculty of Civil Engineering, Department of Geotechnics,
Veveří 331/95, 602 00 Brno, Czech Republic
Erbenová Alexandra
Brno University of Technology, Faculty of Civil Engineering, Department of Geotechnics,
Veveří 331/95, 602 00 Brno, Czech Republic
SYNOPSIS
The article deals with states of stress and deformation to the failure limit state of one Dobrovskeho tunnel tube.
Within the physical modelling the whole tunnel profile was sold with thinking over the influence of lining up to
the limit state. Further, the technology of driving by vertical segmentation excavation was studied.
1. INTRODUCTION
For solving problems at the Institute of Geotechnics connected with the construction of the Dobrovsky tunnel
belonging to the Great City Circuit (GCC) in Brno, physical, or scale models were built up solving the strain and
stress states up to the failure strength for one tunnel tube. We were given the data input necessary for the
formulation of the solution of problems connected with the construction of the Dobrovsky tunnel in models, such
as dimensions of the tunnel, geological conditions and the technological procedure of the construction, by the
GEOtest Brno, which participated in the construction of the Galleries in the tunnel considered.
Within the modelling the following were solved at the Institute of Geotechnics
-
-
The whole profile of the tunnel, considering the lining, the system being loaded up to the failure strength
with the formation of shear surfaces.
The finding of the stability of the provisional rock pillar (middle pillar) between the galleries during the
tunnelling by the vertical division of the purchase including the determination of the optimum length of the
area.
Examination of the rate of extrusion of the foundation into the footwall up to the deformation strength of the
rock pillar.
Inversion analysis during the identification of the deformation of models (shear potential) and using the
stereophotogrammetric analytical method.
The scale models were built up on the basis of dimensional analysis and in accordance with the theory of
similarity. The transition from the tunnelling with the full profile to the technology of tunnelling by the vertical
division was implemented by the set of physical conceptional models (termed by Geo-Brno A, B, C) and
detailed models (denoted by Geo-Brno D1, D2, D3, D4).
2. GEOTECHNICAL DESCRIPTION OF THE MODELLED PLACE AND GENERAL PRINCIPLES
Dobrovsky tunnels of the GCC will be an important part of the basic communication system of Brno-City, but
they will also be a part of the roadway network of the Czech Republic (1/42) and the international European
network (E 461)
The tubes in the length of about 1 000 m will be driven, only the sectors near the portal will be sunk.
The tunnels will be conducted in parallel in the axial distance of about 80 m.
The overall length of the tunnels will be about 1 200 m.
Fig. 1
The geological environment consists of cover layers of loess loams and charges. In the lower horizon in places
there are water-bearing and sandy terraces. The foundation of the terraces consists of Brno calcareous clays of
Neogene (Miocene) age. The clayey massif subsequently also the tunnel tubes proper will be tunnelled.
TRANSVERSAL GEOTECHNICAL PROFILE – PALACKEHO AVENUE
STATIONING 1.39 KM (TUNNEL I) AND 1.38 KM (TUNNEL II)
Fig. 2
Interpolation of the Exploration Probes
Explanation:
123456-
made-up ground
loess loam, light brown, rigid to solid
clayey loam, dark brown, rigid
clayey loam, dark brown, rigid to solid
clay-sandy gravel, and-or sand with gravel with interlayers of clayey loam, water bearing
grey clay, rigid
Physical models were applied at the stationing 1.380 km (tunnel II), i.e. for the sector with low overburden
layers.
Determining for the choice of the technological procedure of the construction is the stability of the rocks, both
from the viewpoints of labour safety, mechanisation of the working methods and also with respect to the
maximum efficiency of the construction performance.
For the use of the technology of tunnelling by the vertical division in cohesive soils it was necessary to identify
the principles of the New Austrian Tunnelling Method for the full profile (section). That is why in the first phase
conception physical models were built (models Geo-Brno A, B, C).
The appropriate forecast of the rock stability is, however, very difficult, because a whole number of factors
affecting one another must be considered. They are above all: the dimensions of the unlined face of the tunnel,
the strength of the rock, its original stress, the size of the stress concentrations brought into the rock by the
breaking, the rigidity of the outfit of the tunnel, the “primary state” and, in the case of clays, the effect of time is
also very important. From those factors we usually only know the dimensions of the face of the tunnel. For the
stability of the face also the orientation and inclination of the rock beds are important. By removing the soil from
the working face of the tunnel the face of the tunnel becomes unstable. The unrigged roof loses its natural
support and the length of the area is thus prolonged by this unwanted way.
That is why the largest risk area is the stability of the face, where at the same time the subsidence of the structure
is threatening. For the implementation of the building of the Dobrovsky tunnel the decisive factor is the stability
of the face and the quality of the technological proceeding of the construction.
The objective of the technological tunnelling in the Geo-Brno models was the determination of the pressures
inside the tunnel necessary for maintaining the stability of the face for the different lengths of the area for
different values of the defined parameters.
From the above it follows that the stability of the face is closely related to the stability of the overlying layers
and the stability of the provisional rock pillar (model Geo-Brno D). Since these problems of stability of the
Dobrovsky tunnel affect the technological procedure of the construction, respecting the changeability of the
properties of rocks in place and time, it was necessary to solve these wide and requiring problems of the stability
of the tunnel also by means of experimental modelling, i.e. by physical models Geo-Brno A, B, C, D and on the
basis of measurements in situ and the results of physical modelling subsequently optimise the calculation
methods. For the solution of stability for all models we started from the theory of limiting states.
3. CONDITIONS OF SOLVING THE TASK BY MODELLING FOR TUNNEL DOBROVSKEHO
To maintain the relation between the model and the reality it was necessary to fulfil the following conditions:




Geo-Brno models have to be geometrically similar to reality
Actions taking place in the Geo-Brno model and in the working have to belong to the same class of
actions.
The initial and edge (boundary) conditions in the model, expressed in the dimensionless form, have to
be numerically identical with dimensionless conditions in the working.
The dimensionless arguments of the same name have to be numerically equal in the model and in the
working.
The following magnitudes (the system of length, mass and time) have the same effect on the state of tension in
the rock massif and the deformation of the outfit of the tunnel:
V1
V2
V3
V4
V5
V6
V7
V8
V9
volume mass
height of overlying beds
physicomechanical modulus
resistance of rock to failure
height of tunnel opening
width of tunnel opening
driving speed
thickness of gunite
reaction of outfit
1
1
1
-2
l
m
t
-3
0
-2
-2
0
0
1
1
1
1
0
1
1
0
0
0
0
0
0
0
0
-1
0
Among the magnitude there exists (on the basis of theory) the relation:
F(V1, V2, V3, V4, V5, V6, V7, V8, V9) = 0
n=9
In determining the dimensionless products we are interested in solving the system of equations. For the
formulation of solving the problems it is necessary to experimentally determine regressive functions of the
critical state of tension necessary for maintaining the tunnel Dobrovského with low overlying beds.
The critical state of tension depends on the following dimensionless parameters:
Pv
Pc
Pk
Pp
Ptm
Pu
ratio thickness of overlying beds to diameter of purchase
value of the ratio of volume density of material multiplied by the average of purchase to coherence
ratio of length of free purchase (attack) to the diameter of purchase
the ratio of the free purchase (drive) to the diameter of the purchase.
the ration of the total maximum strain in the axis of the tunnel before the driving to cohesion
function of the angle of shear strength
4. MODELLING MATERIÁLS, SCALE OF MODELS, METHODS OF MEASURING THE STATE
OF STRAIN AND RESHAPING
The choice and procession of equivalent materials for the model of Dobrovsky tunnel is important, because it
depends on them to what extent the conditions of similarity will be fulfilled. Equivalent materials have to fulfil
the conditions of similarity with the genuine material not only in the basic parameters, such as the volume
density, pressure strength, tension and shear, modulus of elasticity, the Poisson number, but it has also to have a
similar working diagram. Therefore it was necessary to pay close attention to the choice and selection of the
model materials. For solving the stability of the tunnel from EM the law of similarity for the building of the
model are fulfilled by granular materials.
The scale of the model is chosen according to the smallest part of the structure (in our case it is the thickness of
the outfit), which must be feasible. For the Geo-Brno models the Dobrovsky tunnel the scale chosen was 1 : 20.
The purpose of the measurement was to find out as exactly as possible the state of tension, reshaping, coworking of the structure of EM and obtaining information about the actual safety of the work of Dobrovsky
tunnel.
The measurement of the state of stress and reshaping in the physical models Geo-Brno TD carried out by means
of the following measuring and methods:


Fig. 3
measurement of the state of tension by means of pressure cushions
tensometric measuring
o mechanical detectors
o electromechanical resonance-string tensometers
o electromechanical thermometers, core and contact ones
o electrical tensometers – miniature detectors
geodetic and photogrammetric measurement
Scheme of the distribution of mechanical and
electrical miniature sensors in the model
thermometers
Fig. 4
Scheme of the distribution of pressure
cushions and electromechanical for
Geo-Brno models D1, D2, D3 and D4
5. CONCEPTUAL MODELS
In tunnelling with divided cross-sections there arise a number of carrier rings that damage the rock that is why
the New Austrian Tunneling Method (NRTM) prefers the method of tunnelling with a full profile. As the first
step in solving the Dobrovsky tunnel was the implementation of the so-called conceptual models of Geo-Brno A,
B, C.,
Here the circular outfit was considered with the diameter of 6 m for low overhead layers for three cases:
o
o
o
Model A: secured face – variable areas
Model B: secured area – non secured face
Model C: non secured face – variable areas
For the considered models we used a space steel frame “stand” (200 × 200× 200) and in it we formed a frame
structure with the dimensions 200 × 80 × 40 cm. The tunnelling proper of the tunnel work was simulated by a
circular outfit. During the technological procedure of tunnelling an area of elastic, elastic-plastic deformations
and an area of defect were formed. The models were gradually loaded so as to admit the above deformations up
to the deformation, i.e. to the formation of shear faces. For the determination of the shear potential in models A,
B, C we carefully discovered the shear faces and identified them by means of gypsum castings.
The shear faces from the physical models were determined by photogrammetric measurement. The size of the
shear face of model A is 0.4165 m2, of model B 0.2585 m2, of model C 0.2077 m2. From the size of the shear
faces it is evident that the greatest shear potential is that of model A, when there were secured face –
variable areas.
GEO-BRNO TD – MODELS A, B, C (FINISHED BUILDING OF MODELS)
Fig. 5
PHOTOGRAMMETRIC DETERMINATION OF SHEAR AREAS
Fig. 6
Model A after failure
Fig. 7
Exposure of the shear area of model A
Fig. 8
Gradual filling-in of the shear area of
model A with plaster
Fig. 9 Plaster casting of the shear area of model A
with fitting points
DETAIL MODELS (GEO-BRNO TD – D1, D2, D3, D4)
We are led to the division of the purchases by different reasons, above all, however, by the fear of the stability of
the rock mass. In the replacement of big tunnel profiles by several smaller ones (see D1, D2, D3) we must solve
a number of problems, but the basic problem is that of the bearing capacity of the newly formed construction
elements.
The provisional rock pillars, whose bearing capacity will be decisive for the stability of the newly constructed
profile, have the whole area of purchase without the technologically necessary purchase of 124.80 m2, the
width of the purchase is 13.75 m2, and the height of the purchase is 11.8 m2. The purchase is vertically
divided into two lateral purchases with a Gothic vaulting, whose width is 4.755 m and the purchase in the
middle part is 3.475 m wide. In the further phase the gallery will be tunnelled in the calotte, which will connect
the two lateral galleries and in the end the cores will be knocked out that can be divided analogously as the
lateral galleries and the lower part closes as if the whole ring.
The mechanical behaviour of the rock brickwork environment consisting of a great number of elements were
followed in models Geo-Brno D, from the beginning of the activity of forces during the vertical division up to
the possible loss of bearing capacity of rocks or EM forces to overtake and further transport the forces.
If the tunnelling is carried out by the system of vertically ordered partial purchases, then there are formed
temporary rock pillars between them. That is the so-called primary state, i.e., the state when only the primary
outfit of the underground object is active and/or its partial part of purchases, which means that there should not
occur the disturbance of the temporary rock pillar and the face of the underground work TD, which affect each
other.
In tunnelling of the tunnel by the vertical division of the purchase with a Gothic vault the analysis of the state of
tension in the middle pillar is necessary, because the state of tension is decisive for the choice of the
technological procedure of building tunnels and it basically affects the stability of these requiring underground
objects.
ZONING OF THE TUNNEL PROFILE – MODEL D1
Preparation and driving proper of profile D1
Fig. 10
Fig. 11
ZONING OF THE TUNNEL PROFILE – MODEL D2
Fig. 12
Fig. 13
The structure is divided into two lateral purchases with the Gothic vault, which affect the underground
construction considerably. In the division of the second purchase with the Gothic vault the load of the first
purchase with the Gothic vault increases, as well as the size of the deformation of the rock or EM. The second
purchase with the Gothic vault is tunnelled under more difficult conditions, because the original quiet state of
tension is increased by the strains that are concentrated in the surroundings of the second of the first profile.
It is necessary to look for a geometric shape, such as the thickness of the provisional pillar that would still fulfil
the condition that the limiting strength of the rock inside it, under the length of the area, is not exceeded.
INSTALATION OF PRESS AREAS AND THEIR GAUGING
Fig. 14
Fig. 15
FULFILLMENT APPROACH OF A STAND
Fig. 16
Fig. 17
Fig. 18
Fig. 19
GRADUAL SHIFTING OF THE OUTFIT FOR ESTABLISHING SUITABLE LATERAL
CONDITIONS FOR JUDGING THE STABILITY OF THE PILLAR
Fig. 20
Fig. 21
MODEL D3 – TECHNICAL PROCEDURE OF DRIVING FOR THE DETERMINATION OF
PRESSURES NECESSARY FOR MAINTAINING THE STABILITY FOR DIFFERENT LENGTH
OF DRIVE
Fig. 22
Fig. 23
An appropriate forecast of stability in the pillar is very important, because it is necessary to take into
consideration a number of factors affecting each other. They are, e.g., the dimensions of the unlined front, the
original tension and the size of the concentration of the state of tension (mainly during the vertical division), the
rigidity of the outfit and the effect of time. Therefore it was necessary to investigate the real state of the TD and
the behaviour of the rock (EM) and their mutual action.
In the technological procedure of the building of TD by vertical division (the state of D1, D2, D3) to the final
state of the full profile of D4, in the course of the expansion of the breakout of the calotte, in examining the core
of the purchase and breakout for the lower vault conspicuous changes in the state of tension were observed and
deformation of the given area.
The model Geo-Brno D4 respected special mechanical behaviour of the brick veneer (in the division D1 to the
state D4) so that it might fulfil its mission reliably and for the whole time of the technological procedures of the
building. The state of tension and the deformation of the model Geo-Brno D4 were exactly determined.
Summarising the results of the model Geo-Brno D4, it is evident that the ratio of the forced volume change to
the volume change evoked by the mechanism of deformation, determines, besides the condition of deformation,
also the critical state of tension.
MODEL D4
Fig. 24
Fig. 25
Fig. 26
Fig. 27
The outfit of the tunnel, i.e. gunite and reinforcing elements were replaced for the model, on the basis of
similarity, with Plexiglass of the thickness of 3 mm and Novodur of the diameter 1.6 cm. In the model 7
purchases were applied (7 reinforcing elements). Electrical miniature sensors were applied to the middlereinforcing element.
Fig. 28 Formation of the shear surfaces for the limiting loading
6. CONCLUSION
The analyses of the models Geo-Brno D1, D2, D3 unambiguously determined the increased horizontal and
vertical states of tension in the middle pillar. In model tests of Geo-Brno TD the loading of the primary lining
(D1, D2) in the middle pillar was 2.8 times higher than that of the external primary lining and the vertical
load was 3.9 times higher than the horizontal loading. The above results confirm a great overload of the
middle pillar and the technological procedure must respect the length of the area to maximum 95 cm.
The tension strength due to the outer loading on models was 0.0151 MPa. On the basis of the dimensional
analysis and the method of similarity the limiting value 0.4379 MPa was determined for real models (TD).
Physical scale models confirmed the fact that if the technological procedure of building the Dobrovsky tunnel is
observed, the technology of tunnelling by the vertical division is applicable.
LITERATURE
WEIGLOVÁ,K. Conception solution of the effect of technology in building the tunnel Dobrovskeho in Brno. In
Sborník 31. konference “Zakládání staveb Brno 2003”, konané v Brně (Proc. of the 31th Conference
Foundations Brno 2003), Akademické nakladatelství CERM, 2003, s. 39 – 43, ISBN 80-7204-304-8
WEIGLOVÁ,K. The solution of conceptual problems linked with the construction of a tunnel. In Proc.
Computer Methods and Advances in Geomechanics. The University of Arizona Tucson, USA. Rotterdam, AA
Balkema, 2001.
PROCHÁZKA,P., WEIGLOVÁ,K. Coupled modelling using DSC and TFA models. In Proc. 2nd International
Conference on Theoretical, Applied, Computational and Experimental Mechanics (ICTACEM2001). Kharagpur,
India Indian Institute of Technology, 2001, pp 12
DESAI,C.S., SALAMI,M.R. A constitutive model and associated testing for soft rock, p. 299 – 307, In: Int. j.
rock Mech. Min. Sci. &geomech. abstr., Vol. 24, No 5, 1987
DESAI,C.S., SOMASUNDARAM,S, FRANTZISKONIS,K. A hierarchical approach for constitutive modelling
of geologic materials, p. 225 – 257, In International journal for numerical and analytical methods in
geomechanics, Vol. 10., 1986
The contribution was elaborated as part of the grant project GA ČR No 103/03/0483.