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Rational interpretation of tunneling considering existing tunnel and building loads
Interprétation rationnelle du creusement des tunnels prenant en compte les tunnels préexistants
et les charges liées aux constructions
Shahin H. Md., Nakai T., Iwata T.
Department of Civil Engineering, Nagoya Institute of Technology, Nagoya, Japan
ABSTRACT: In this research, model tests of twin tunnels excavation are conducted changing the position of following tunnel. It is
also demonstrated the interaction effect between tunneling and existing nearby structures in this paper. The corresponding finite
element analyses are also conducted using FEMtij-2D software with elastoplastic subloading
t
ij
model. It is revealed that the earth
pressure distribution and ground movements during tunnel excavation depend on the distance and position between the twin tunnels.
It is also found that there is a significant effect of tunneling on the existing foundation of building even the tunnel is constructed in
deep underground. The numerical results show very good agreement with the results of the model tests.
RÉSUMÉ : Dans ce travail, des essais sur modèles réduits du creusement de deux tunnels adjacents ont été réalisés dans lesquels la
position du tunnel suivant a été changée. On montre
l’effet de l’interaction entre le creusement et les structures environnantes. Des
simulations par la méthode des éléments finis ont également été réalisées en utilisant le code FEMtij-2D et le modèle de
comportement élastoplastique
t
ij
basé sur le concept de subsurface de charge. Les résultats montrent que la distribution de la pression
des terres et les mouvements du sol durant le creusement du tunnel dépendent de la distance et de la position des deux tunnels
adjacents. Ils montrent également qu’il y a u
n effet significatif du creusement sur les fondations des constructions existantes même si
la profondeur du tunnel est importante. On obtient une très bonne concordance entre les résultats expérimentaux et numériques.
KEYWORDS: tunnel excavation, model tests, finite element simulations.
1 INTRODUCTION
The behavior of the ground during tunnel excavation is usually
investigated conducting model tests where absolute
displacement is applied in the boundary of the tunnel periphery
or stress around the excavation face is applied. In our previous
research (Shahin et. al 2004 & 2011), we developed a tunnel
apparatus to simulate tunnel excavation where the cross section
of the tunnel is circular. In that device the tunnel was made in
this way that the movement of the tunnel itself was not allowed.
But, a real field tunnel is free to move in the vertical and
horizontal directions. To consider this important point, in this
research further modification of the model tunnel apparatus has
been done for allowing the movements of the tunnel together
with the soils of the ground. The device allows the movements
of the tunnel itself with satisfying the equilibrium between
tunnel and the surrounding ground. In this research, model tests
of twin tunnels excavation are conducted changing the position
of following tunnel with the new apparatus.
Nowadays, urban tunneling in deep underground is
increasing all over the world. In Japan, in the design of tunnel
construction it is not usually considered the effect of tunneling
on existing structure if a tunnel is constructed in deep
underground (more than 40m deep ground) and the vertical
distance from the foundation of existing structure is more than
10m. To investigate the effect of tunneling on existing structure,
model tests of tunneling are also performed in deep
underground considering existing building. The corresponding
numerical simulations are performed using FEMtij-2D software.
Subloading
t
ij
model is used as an elastoplastic constitutive
model for the ground material. This model can describe typical
stress deformation and strength characteristics of soils such as
the influence of intermediate principal stress, the influence of
stress path dependency of plastic flow and the influence of
density and/or confining pressure.
2 DESCRIPTION OF MODEL TESTS
Figure 1 shows the tunnel apparatus after the modification of
the previous tunnel device (Shahin et. al (2011)). In the new
apparatus, the excavation part can be moved upward and
downward, and left and right without friction by a bearing and a
horizontal slider attached in the device. The weight of the entire
model tunnel is balanced with the counter weight applied
through a fixed pulley set at the top of the device. As a result,
the tunnel excavation can be simulated by leaving it to an
equilibrium condition of the vertical and lateral earth pressures
controlling the amount of shrinkage of the tunnel diameter. The
total diameter of the tunnel is 100mm. Figure 2 shows the
layout of the apparatus having two model tunnel devices; both
tunnel devices have the same dimension as described in Fig.1.
In the apparatus 12 load cells are used to measure earth pressure
acting on the tunnel. The load cells are attached with blocks
which are placed surrounding the segments of the tunnel.
Therefore, earth pressure can be obtained at 12 points on the
periphery of the tunnel at a time.
The dimension of the apparatus is chosen with a scale of
1:100 between the model and prototype scales. Mass of
Counter
weight
Rail
Shaft
Stopper
Pulley block
Motor
Stand
Side view
Back view
Laser disp.
transducer
Figure 1. Schematic diagram of tunnel device.
