2984
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
10
-1
10
0
10
1
10
2
12
10
8
6
4
2
0
100
200
300
400
Time (years)
Settlement (m)
Embankment load (kpa)
0 kPa (Current state)
54 kPa (lightweight banking)
79 kPa (replace with curvert)
105 kPa
Reduction in load
embankment. Furthermore, residual settlement was reduced by
approximately half due to the fact that the settlement
approached
convergence
earlier.
However,
because
consolidation of the deep peat layers also occurred earlier,
deformation was concentrated in the upper peat layers, and
upheaval of areas near the toe of the slope increased (Figure
omitted). Potential countermeasures for this problem associated
with expansion of SD-improved area, include expanding the
area and load of the counterweight embankment and reducing
the rate of embankment loading, particularly in the initial stages.
4.2
Effect of slow banking method
Table 1 shows the results of simulations performed under the
same conditions as Case 3 above, but with lower (1.5 cm/day)
or higher (3.0 cm /day) rates of embankment loading. Reducing
the rate of loading allowed for greater drainage during loading,
which resulted not only in earlier convergence of settlement and
reduction in residual settlement but also a slight but significant
reduction in total settlement. Although the data is not presented
here due to space constraints, the lower loading rate was
effective in reducing lateral displacement of the shallow ground
layers and upheaval of the soil surface, and resulted in an earlier
shift from outward deformation to inward deformation in the
embankment loading process.
Figure 8 Effect of weight reduction of the existing embankment.
5 CONCLUSION
In this paper, we attempted to simulate the large-scale
settlement in excess of 11 m and predict future settlement of
ultra-soft ground containing peat due to loading by a test
embankment. When the stress state of peat exceeds the
consolidation yield stress under heavy loading, the undrained
shear deformation resulting from poor permeability causes large
lateral displacement to occur, which can lead in severe cases to
slip failure. Furthermore, because rapid compression occurs
even under drained conditions in peat layes, permeability
improvement using SD, reduction of the loading rate, and the
more drastic countermeasure of reducing the load itself are
effective in increasing stability during loading, reducing the
deformation of the ground surrounding the embankment, and
reducing residual settlement after the enter into service.
Table 1. Effect of rate of embankment loading.
Loading rate
(increase in embankment
thickness/day)
Total
settlement
(m)
Residual
settlement
(cm)
1.5cm/day
11.7
74
2.35cm/day
11.9
87
3.0cm/day
12.0
94
Although construction of the test embankment shown in Figure
5 (a) was managed so that the embankment “height” generally
increased at a rate of 3.0 cm/day, because obvious settlement
occurred during embankment construction, the actual rate of
loading per unit time (increase in embankment “thickness”) was
higher than that specified in any of the above simulations.
Although no catastrophic slip failure occurred, this rapid
construction resulted in increased lateral displacement and
upheaval. Slow embankment loading is effective not only for
increasing stability during construction but also for reducing
residual settlement and impacts on the adjacent ground. When it
is not possible to secure adequate time for embankment
construction, combinations with other countermeasures such as
vacuum consolidation should be considered.
6 REFERENCES
Asaoka, A. 1978. Observational procedure of settlement prediction,
Soils and Foundations
, 18(4), pp.87-101.
Asaoka, A., Noda, T., Yamada, E., Kaneda, K. and Nakano, M. 2002.
An elasto-plastic description of two distinct volume change
mechanisms of soils,
Soils and Foundations
, 42(5), pp.47-57.
Asaoka, A. and Noda, T. 2007. All soils all states all round geo-analysis
integration,
International Workshop on Constitutive Modeling -
Development, Implementation, Evaluation, and Application
, Hong
Kong, China, 11-27.
Inagaki, M., Nakano, M., Noda, T., Tashiro, M. and Asaoka, A. 2010a.
Proposal of a Simple Method for Judging Naturally Deposited Clay
Grounds Exhibiting Large Long-term Settlement due to
Embankment Loading,
Soils and Foundations
, 50(1), 109-122.
4.3
Effect of lightweight banking method
Figure 8 shows the effect of weight reduction of the existing
embankment with lightweight materials. For simplicity, in the
simulation, the reduced loading was represented by removal of
the embankment. Greater reduction in loading was accompanied
by less residual settlement and earlier occurrence of settlement
convergence. Furthermore, although not shown here, it was
demonstrated that greater reduction in loading resulted in
reduced inward deformation of the ground surrounding the
embankment.
Inagaki, M., Sakakibara, K., Yamada, K., Tashiro, M., Noda, T. Nakano,
A. and Asaoka, A. 2010b. Estimation of the initial conditions of a
very soft peat ground which causes large delayed settlement due to
test embankment loading, 45th Japan National Conference on
Geotechnical Engineering, 751-752 (in Japanese).
Noda, T., Asaoka, A., Nakano, M., Eiji, Y. and Mutsumi, T. 2005.
Progressive consolidation settlement of naturally deposited clayey
soil under embankment loading,
Soils and Foundations
, 45(5), 39-
51.
Noda, T., Asaoka, A. and Nakano, M. 2008. Soil-water coupled finite
deformation analysis based on a rate-type equation of motion
incorporating the SYS Cam-clay model,
Soils and Foundations
,
48(6), 771-790.
Based on these simulations, the culvert in actual construction
site has been designed with a 1.2-m freeboard, and in order to
reduce differential settlement, the material of the embankment
in the vicinity of the culvert is planned to be replaced with
lightweight material.
Šuklje L. 1957. The analysis of the consolidation process by the
isotaches method,
Proc of 4th Int. Conf. on Soil Mech. Found.
Engng.,
London, 1(1), 200-206.
Tashiro, M., Noda, T., Inagaki, M., Nakano, M. and Asaoka, A. 2011.
Prediction of Settlement in Natural Deposited Clay Ground with
Risk of Large Residual Settlement due to Embankment Loading,
Soils and Foundations
, 51(1), 133-149.
Terzaghi K. 1943. Theoretical soil mechanics,
John Wiley and Sons
.
