1736
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
2 FINITE ELEMENT MODELLING OF EXCAVATION
AND ADVANCEMENT OF THE BOX-MODULES
Figure 2 shows the excavation and insertion processes of box-
jacking operation in the modular approached tunnelling method,
forward by applying mechanical pull jack forces and excavating
the tunnel boring machine and the box-module are driven the
soil in front of the tunnel boring machine with its cutting face.
The magnitude and distribution of the ground deformations are
largely controlled by the construction processes of each box-
jacking. Therefore, when estimating the ground deformation
caused by the modular approached tunnel construction, care
should be taken of how to model the characteristics of the
machine and the construction processes.
Because of the complex boundary conditions of a box-jacking
tunnelling problem, the use of the finite element method is one
of the useful methods to investigate the ground deformation
behaviour. In reality, the stress-strain state of the soil changes
continuously as the tunnel boring machine and the box-module
advances. Then, in order to fully understand the ground
deformation mechanism associated with box-jacking, the
deformation caused by excavation and insertion processes of the
box-module needs to be investigated.
In this study, the excavation process is modelled by
introducing excavating finite elements in front of the tunnel
boring machine (Komiya K. et.,al. 1999). The advancement of
the tunnel boring machine is modelled by (i) remeshing the
finite elements at each time step, (ii) introducing the excavating
finite elements of a fixed size in front of the tunnel boring
machine, and (iii) applying external forces for the advancement
of the machine and box-module. Sequential illustrations of the
modelling of the excavation at the cutting face of the tunnel
boring machine (TBM) and the advancement of the machine
and box-module are shown in Figure 3.
Figure 3(a) shows the status of the tunnel boring machine and
box-module at reference time t0. In or-der to model the external
pull forces applied to the tunnel boring machine, forces are
applied at the nodes of the tunnel boring machine. During the
time interval of t0 to t0+dt, the excavating elements and the soil
elements adjacent to the tunnel boring machine elements will
deform by the external force (Figure 3(b)). The tunnel boring
machine will act as rigid bodies since a large value of stiffness
is used for the elements representing the tunnel boring machine.
After obtaining a solution for t = t0+dt, the finite elements are
remeshed as shown in Figure 3(c). The new mesh will have the
same mesh geometry relative to the tunnel boring machine as
Figure 3. Advance of the box-module simulated by using the
excavating elements.
t= t0, but the location of the tunnel boring machine and box-
module has shifted. Again, the excavating elements will be
placed in front of the cutting face before applying external
forces given for the next time step. By doing so, the
construction processes of the box-module and the associated
stress-strain changes of the ground are numerically simulated in
a continuous manner.
Figure 4. The formation of the box-modules (lining frame) and the site stratigraphy on the cross section.
Advancing segmental box
(a) t=
(b) t= +dt
(c) t= +dt
Excavating elements
Finite elements were remeshed.
Pull jack forces
Joint elements
Ground
Tunnel boring machine
and box-module
5.52
4.31
1210
8140
850
850
850
10885
9660
23095
6170
2900
Bank
Fine Sand
Silt
11950
6170
3180
F.L.
Diluvial Mud Stone
（
mm)
Tunnel
GL-5.12m
0
SPT-N
50
50<
