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Where
is the non opening ratio;
1
is the friction
coefficient between soils and the cutterhead; R
c
is
the radius of the cutterhead, m; R
d
is the active
pressure of soils, kPa.
The friction torque of the back side of the
cutterhead is regard as the same as that of the front
side.
Through calculation, the cutting torque is 473
kNm, the friction torque for each side of cutterhead
is 512 kNm. So the total torque is 1497 kNm. The
average error between the simulated torque and the
calculation torque is 4%, which illustrates the DEM
model is correct.
4 PARTICLE MOVEMENT
RULES
During the DEM simulation, the displacement
distributions of soil particles in the chamber and in
the cutterhead are displayed at tunnelling time 0s,
10s, 15s, 20s, 30s, 45s and 60s.
As shown in Figure 4, at time 0 s, the cutterhead,
the shield and the screw conveyor haven’t started to
work, the particles in the cutterhead and in the
chamber both move downward to the chamber board
under the gravity and the ground pressure. The soil
displacement in the cutterhead is higher than that in
the chamber.
At time 10 s (Figure 5), the particles in the
cutterhead rotate along the axis of y anticlockwise. It
is because that the friction torque caused by the
cutterhead conquers the interaction force between
particles, and the cutterhead leads the particle to
move. The bottom particles in the chamber march
toward the screw entrance for the screw rotation.
The above particles in the chamber rotate
anticlockwise.
At time 15 s (Figure 6), in the cutterhead, the
particles displacement in XZ plane is radiate. This is
because that in the circumferential direction, the
distance between particles increases with the
cutterhead rotation further, leading to the interaction
force between particles increases; When the
interaction force is larger than the friction caused by
the cutterhead rotation, the particles slow down the
movement anticlockwise until the velocity of the
particles in circumferential direction reach 0. At this
time, the displacement of particles is subjected to the
radial ground pressure, so the displacement of
particles is radial in XZ plane. The displacement of
particles in the chamber is similar to that at time 10.
At time 20 s (Figure 7), the particles rotate
clockwise in the cutterhead. This is because that the
interaction force between particles is much larger
than the force caused by the cutterhead rotation. At
time 15 s, the force between particles reaches
maximum. By the particles rotate clockwise, the
distance between particles reduces, and the
interaction force between particles reduces too.
When the interaction force reaches 0 N, the particles
begin rotate anticlockwise again. In the chamber, the
bottom particles move toward the inlet of the
conveyor for the screw rotation, and the movement
direction of the above particles is caused by the
ground pressure mainly.
At time 30 s and 60 s (Figure 8 and Figure 10),
the displacement distribution of particles is similar
to that at time 0 s. As shown in Figure 9, the
displacement is similar to Figure 6. It implies that
the motion period of the soil particles is 30 s.
In order to study the relation between the rotation
speed of the cutterhead and the soil particles
movement rules, the DEM model is run again setting
the cutterhead rotation speed 1 rpm. The
displacement distribution of soil particle at run time
30 s is shown in Figure 11. It is shown that the
displacement at time 30 s when cutterhead rotation
speed is 1 rpm is similar to the displacement at time
15s when cutterhead rotation speed is 2 rpm. So the
particle movement period T can be deduced as
equation (3)
60
T
n
(3)
5 CONCLUSIONS
The DEM model of the EPB shield machine
tunnelling was established, and the simulated
cutterhead torque was consistent with the theoretical
calculation results, which illustrated the model was
correct.
The displacement distribution of soils in the
chamber and in the cutterhead during the shield
machine tunnelling was obtained. The distribution
presented periodic variation, and the movement
period of soil particles is related to the cutterhead
rotation speed.
Seen from the figures of displacement
distribution, the soil displacement in the cutterhead
is determined by the cutterhead rotation, the
ResearchonMovementRulesofSoilParticlesduringEPBMachineTunnelingwithSpokeCutterhead
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