512
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
*(
1)/
*( 1)/
(1 )
p
p
d
d
k
k
k
k
c
(1)
where γ is a key dimensionless factor, which is a function of
wedge angle of cutter , elastic constants and plastic strength
parameters.
*
*
*
u
i
= E, or G , q , , , ,
(2)
and ξ is defined as dimensionless elasto-plastic (E-P) radius
while ξ* reach critical value where brittle fracture occurs on this
E-P interface. Thrust force, therefore, can be estimated using the
indentation pressure P and indentation force F as seen in Figure
2 schematically.
p
p
n (K 1)/K
p
*
p
p
(n 1) K
P 1
1
q K 1 K n
(3)
n 1
i
d
F (3 n)
P(
)
tan
β
(4)
d
Intrinsic
flaw
Core
Plastic zone
Elastic zone
2a
*
r
Indenter
F
E-P
interface
, max
x
X
y
Figure 2. Schematic normal indentation fracture
2.2
Generalized trust system
This study presents a generalized trust system of cutter head
globally by taking each different types of individual cutters into
account locally with respect to different methods (TBM, ST,
and PJ) and geological conditions (rock, soil, & gravel). Figure
3a and 3b show the total trust force F, which is consists of front
resistance F
f
and lateral resistances F
p
including both F
p,m
for
machine itself and Fp,p for pipes.
f
p,m p,
F F F F
p
(5)
p,p
F
p,m
F
f
F
F
p
F
Figure 3a. Trust force system
Figure 3b. Trust force system with inclined angle
Therefore, Ff (kN) is estimated from different types (nj) of
cutters fj and water/earth pressure Ps (kN/m2):
m
f
j
j
s
j 1
F n f P
A
(6)
where A is cross area of cutter head (m
2
).
This paper presents an analytical estimation to deal with
different mechanical cutting methods (tunnel boring machine,
shield tunnel and pipe jacking), construction types (earth
pressure balance, slurry pressure balance, thick-mud), and
geological conditions (soil, gravel and rock) by generalizing
their total thrust system. The straight-line thrust is calculated for
either wedge- or conical-typed cutters of tunneling machine. In
this generalized work, the upper bound and lower bound of trust
are highlighted for the warning situations for risk assessment.
3 CASE STUDY
3.1
Case I: Taoyuan tunneling project in Taiwan
In addition, the in-situ data of trust in shield machine
(Taoyuan tunneling project) is presented to confirm with. It
depicts a favorable agreement for the estimation of thrust in this
study as shown in Figure 4 (cutter head), and Figure 5 (results)
with respect to normal cutting as well as abnormal conditions
(point a and b shown in Fig.5) once the in-situ data out of the
theoretical boundaries.
Figure 4. Cutting head in field for shield tunnel project
