1776
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
Figure 10 represents the observed and computed shear strain
distribution for soil cover of
D/B
=1.0 in the case of flat
foundation. Figure 11 shows the same for the pile foundation
where the tunnel is constructed in the deep underground
(
D/B
=4.0). As shown in the figures that the shear band of the
ground is developed during the tunnel excavation and it spreads
towards the strip foundation from the sides of the tunnel. In the
deep underground, a large shear strain due to tunnel excavation
concentrates to the rear pile for the case of
D
p
/B
=1.0, where
D
p
is the vertical distance between the pile tip and the tunnel crown.
Because of the disturbed initial stress, the development of the
shear band is different in the left and right side of the tunnel.
The effect of the tunneling to the existing structure mainly
depends on the distance between the tunnel and foundation of
the structure. The computed distributions of shear strain of the
numerical analyses show very good agreement with the results
of the model tests.
Figure 10. Strain distribution
–
strip foundation (
D/B
=1.0)
Figure 11. Strain distribution
–
pile foundation (
D/B
=4.0)
Figure 12 shows the earth pressure distributions for the strip
foundation when
D/B
=1.0. Figure 13 shows the same for the
pile foundation where
D/B
=4.0 and
D
p
/B
=1.0. Here, the dotted
curves with black circular marks represent the earth pressure
levels before applying the building loads, while the black solid
line represents the pressure levels after applying the building
loads, and the red solid line represents the earth pressure of the
greenfield condition for
d
r
=4.0mm. The earth pressure at the
foundation side increases after applying the building loads. It
decreases to some extent around the tunnel after performing the
tunnel excavation except at the invert which is the opposite side
of the foundation. An unsymmetrical earth pressure distribution
was seen around the shallow tunneling, and the final earth
pressure distributions were different from those of the
greenfield condition. Therefore, the effect of the soil-structure
interaction should be properly contemplated in the earth
pressure computation around the tunnel lining even in the
tunneling of deep underground. The results of the simulations
slightly differ from the measured earth pressure levels around
the tunnel invert. As a whole, the subloading
t
ij
model simulates
well the earth pressure distribution of the model tests in the case
of the soil-structure interaction problem.
Figure 12. Earth pressure distribution
–
strip foundation
Figure 13. Earth pressure distribution: pile foundation (
D/B
=4.0)
5 CONCLUSIONS
From the model tests and numerical simulations it is found that
for the excavation of the preceding tunnel earth pressure
decreases around this tunnel as expected, however, the earth
pressure at both side of the tunnel increases and it decreases at
the tunnel invert during the excavation of the following tunnel
when the following tunnel is placed directly underneath of the
preceding tunnel. On the other hand, when the following tunnel
is placed diagonally downward earth pressure of the preceding
tunnel increases at the right shoulder and the left part of the
tunnel invert. A region of large deviatoric strain concentration is
seen between the twin tunnels due to excavation of the
following tunnel. Therefore, the interaction of parallel tunnels
should be predicted carefully for proper and safe design for the
closely spaced 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
analyses perfectly capture the surface settlement, ground
deformation and distributions of earth pressure of the model
tests.
6 REFERENCES
Adachi, T., Tamura, T., Kimura, M. and Aramaki, S. 1994. Earth
pressure distribution in trap door tests:
Proc. of 29
th
Japan National
Conference of SMFE
, 3, 1989-1992 (in Japanese).
Murayama, S. and Matsuoka, H. 1971. Earth pressure on tunnels in
sandy ground:
Proc. of JSCE
, 187: 95-108 (in Japanese).
Nakai, T., and Hinokio, M. 2004. A simple elastoplastic model for
normally and over consolidated soils with unified material
parameters.
Soils and Foundation.
44(2): 53-70.
Shahin, H.M., Nakai, T., Hinokio, M., Kurimoto, T.and Sada, T. 2004.
Influence of surface loads and construction sequence on ground
response due to tunneling,
Soils and Foundation
, 44(2), 71-84.
Shahin, H. M., Nakai, T, Zhang, F., Kikumoto, M. and Nakahara, E.
2011. Behavior of ground and response of existing foundation due
to tunneling,
Soils and Foundations
, 51(3), 395-409.