Geoscience Reference
In-Depth Information
Bolton and Pang (1982) give the following reasons as the justification for
performing centrifuge tests rather than simpler conventional model tests of a
reinforced earth wall:
1. By creating an equality of stress in the model with that in a typical field-
scale wall, the proper dilatancy of the soil is reflected; the sand in
conventional small models dilate extremely strongly, and this must
distort failure mechanism;
2. By enhancing soil stress, the requirements for the reinforcement are
similarly increased, so that the additional stiffness created by strain
gauges and lead wires is insignificant for the already substantial ties;
3. Because the materials are thicker, the strength of the joints can be more
easily controlled and the impact of local imperfections is reduced.
Reason (1) is the main advantage of a centrifuge explained in the above
section. Regarding the advantage from reason (1), someone may argue that from
Eq. (6) a proper simulation of the behavior of the prototype consisting of
cohesionless soil would be possible in a small-scale gravity model, if the
dilatancy of the prototype soil can be created by modifying the relative density of
the soil. Even if it is possible, there are considerable difficulties in modeling the
reinforcement, which are mentioned in reasons (2) and (3). Table 1 shows the
Table 1
Scaling Factors in Centrifuge Model
Parameter (dimension)
Scaling factor (m/p)
Acceleration (L/T
2
)
l
a
¼
N
l
L
¼
1/N
Length (L)
Area (L
2
)
l
A
¼
1/N
2
Soil density (M/L
3
)
l
r
¼
1
Force (ML/T
2
)
¼
(F)
l
F
¼
1/N
2
Stress (F/L
2
)
l
s
¼
1
Particle size (L)
l
P
¼
1
Permeability (L/T)
l
k
¼
N
Cohesion (F/L
2
)
l
c
¼
1
Stiffness (F/L
2
)
l
E
¼
1
Time: inertia (dynamic) (T)
l
Ti
¼
1/N
l
Tf
¼
1/N
2
Time: laminar flow (T)
Time: creep (T)
l
Tc
¼
1
l
Rs
¼
1/N
2
(1/N
*
)
Reinforcement tensile force (F)
Reinforcement strain
l
Re
¼
1
*
Per unit length.
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