1278
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
0
20
40
60
80
100
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
Case1-1(before)
Case1-1(after)
u
2
Number of cyclic ,
N
0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14
0.000
0.005
0.010
0.015
0.020
0.025
0.030
Before repair
After repair
u
2
(mm)
Figure 9. Relationships between displacement
u
2
and number of cyclic
loadings in Case 1-1 before and after tie-tamper implementation
Parameters
u
2
,
C
,
, and
in Eq. 1 were evaluated from 100
cyclic loadings conducted before and after tie-tamper
implementation. The relationships between
u
2
and the
remaining three parameters before and after tie-tamper
implementation are shown in Figs. 10, 11, and 12.
Figure 12. Relationships between displacement
u
2
and degree of gradual
settlement
Figure 10 shows that
were in the range 0.9–1.5 before tie-
tamper implementation regardless of roadbed type and ballast
thickness. Here,
represents the duration periods of the initial
settlement process (Eq. 1). The figure also shows that
decreased more after tie-tamper implementation than that before.
This tendency can be clearly observed when
u
2
is higher, which
indicates that the duration periods of the initial settlement
process increased after tie-tamper implementation.
Parameters
C
and
proportionally increased with an
increase in
u
2
, as shown in Figs. 11 and 12. Here,
C
represents
the amount of initial settlement, and
represents the degree of
the gradual settlement. Figure 11 shows a higher decrease in
C
after tie-tamper implementation than that before. The same
tendency was also clearly observed at higher
u
2
because
roadbeds became denser as a result of cyclic loadings; therefore,
the amounts of initial settlement decreased after tie-tamper
implementation. Conversely, Fig. 12 shows that
was nearly
the same after tie-tamper implementation as that before. These
results suggest that although the characteristics of the initial
settlement process are significantly altered after tie-tamper
repair, the degree of gradual subsidence is minimal regardless of
ballast thickness and roadbed type.
0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Before repair
After repair
u
2
(mm)
4 CONCLUSION
The effects of ballast thickness and tie-tamper repair on the
settlement characteristics of ballasted tracks were investigated
by conducting a series of cyclic loading tests on model grounds.
The following conclusions were derived from this research:
(1) The standard 250 mm ballast thickness is ineffective for
minimizing settlement, particularly when the nonlinearity of
roadbed compressibility is relatively moderate.
(2) The characteristics of the initial settlement process are
altered considerably after tie-tamper implementation; however,
the degree of gradual subsidence is minimal regardless of
ballast thickness and roadbed type.
Figure 10. Relationships between displacement
u
2
and duration periods
of the initial settlement process
5 ACKNOWLEDGEMENTS
The authors would like to thank Mr. Kazunori Ito of the
Railway Technical Research Institute for his assistance in
conducting experiments.
0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14
0
2
4
6
8
10
Before repair
After repair
C
u
2
(mm)
6 REFERENCES
Ishikawa, T. and Namura, A. 1995. Cyclic deformation characteristics
of the railroad ballast in full scale tests, Journal of JSCE, No.512,
47-59 (in Japanese).
Sekine, E., Ishikawa, T and Kouno, A. 2005. Effect of ballast thickness
on cyclic plastic deformation of ballasted track, RTRI Report, Vol.
19, No.2, 17-22 (in Japanese).
Figure 11. Relationships between displacement
u
2
and amount of initial
settlement
C
