1788
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
between the maximum and minimum stress values is not more
than 52 kPa.
‐220000
‐200000
‐180000
‐160000
‐140000
‐120000
‐100000
0
10
20
30
40
St ress/ Pa
The distance from left slope foot/m
Test results after backfilling
Test results after waterway excavation
Numerical results after backfilling
Figure12. Stress distribution of the bottom of E section foundation
trench
In the standard condition of C section, 3 years after
construction, the largest settlement is 0.02035m. In the
condition of 1m cushion, the largest settlement is 0.0307m after
construction, which indicates that reduced cushion makes
settlement larger than the settlement of standard conditions.
After the test, the cushion under the standard condition (1.5m
cushion) has no significant change in centrifuge. But under the
non-standard condition (1m cushion), most gravel cushion has
been incorporated into the clay layer in centrifuge after the test,
which blend the part of cushion and clay layer. And the cushion
lost its attempted function, which is also the main reason for the
difference between non-standard conditions and standard
conditions.
The stress distribution curve of IMT base groove bottom
surface of C section under the standard condition (1.5m cushion)
and non-standard condition (1m cushion), 3 years after
backfilling is shown in Figure 13.
4 CONCLUSIONS
Figure 13 indicates that the basal stress curve of non-standard
condition has large gradient, which means that the basal stress
extremum difference under the non-standard conditions is larger
than the basal stress extremum under standard conditions. 1.5m
cushion is better than 1m cushion in terms of foundation stress
uniformity. For both sides base disengaging of IMT condition,
the center stress of IMT’ base is smaller than the center stress of
IMT’ base under the standard condition. But the basal stress
with voids underneath is significantly higher than the stress
under the standard condition ; the basal stresss close to both
sides of IMT is larger than the stress under the standard
condition. The reason is that because of both sides base
disengaging of IMT, in the overlying loads, backfilling leads to
the cushion bearing loads at the begining, then clay was
squezzed out and underneath voids were formed. Stress
concentration occured at the boundaries of voids b under IMT’
base . Since IMT is of a certain stiffness, the strain of both sides
of IMT will not increase excessively and the basal stress of
void beneath is relatively reduced.
For the special conditions of Hong Kong-Zhuhai-Macao bridge
undersea IMT on Deep Soft Subsoil with Heavy Siltation in
Open Sea, the stress process of IMT foundation soil in different
conditions is simulated by using of Geotechnical Digital
Systems and numerical simulation based on on-site CPTU test
results and the in-situ bored soil sample. The stress path of the
process of the foundation soil consolidation- excavation -
backfill recompression - waterway excavation are studied. The
deformation characteristics of foundation soil at typical cross
section is simulated by numerical analysis.
Based on these results, a construction simulation was
performed with geotechnical centrifuge for the process of
subsoil consolidation – excavation – sinking IMT – backfilling
– siltation as well as the re-excavation of channel. The results
show that the settlement of IMT foundation soil in construction
and post-construction is smaller. After 3 years of operation, the
foundation cumulative settlement amount on deep channel
section and thick soft clay ground is not more than 0.0407m. In
the process of excavation and backfill recompression, the stress
and settlement distribution of foundation cross-sectional has a
saddle-shaped distribution, and the different deformation value
between foundation cross-sectional and longitudinal section is
small. Waterway excavation has less effect on the stress and
deformation of the IMT foundation soil. Cushion thickness has
a greater impact on the settlement of IMT, and 1.5m cushion
thickness is reasonable.
- 500000
- 400000
- 300000
- 200000
- 100000
0
10
20
30
40
50
St r ess/ Pa
The di st ance f r oml ef t sl ope f oot / m
Test r esul t s of 1. 5mcushi on
Test r esul t s of 1mcushi on
Two ends of I MT voi d beneat h
5 ACKNOWLEDGEMENTS
Figure13. Stress distribution of the bottom of the C section foundation
trench
This work was financially supported by The Project was
Supported by Design and Construction Key Technology of
Super Long Immersed Tunnel on Deep Soft Subsoil under
Heavy Siltation in Open Sea, National Science and Technology
Support Program (2011BAG07B01).
The typical cross section ground deformation curve with
time, within 3 years after the completion of the construction
backfill is shown in Figure 14.
6 REFERENCES
Lambe T W
，
Stress Path Method
，
Journal of the Soil Mechanics and
Foundation Division
，
ASCE
，
1967
，
93
（
SM6
）：
309-331
Takeji Kokusho
，
Tadashi Hara
，
Ryousuke Hiraoka
，
Undrained Shear
Strength of Granular Soils with Different Particle Gradations[J].
Journal of Geotechnical and Geoenvironmental Engineering
，
2004
，
130
（
6
）：
621-629
- 0. 01
0
0. 01
0. 02
0. 03
0. 04
0. 05
0
200 400 600 800 1000 1200
Ti me/ d
The di spl acement af t er
const r uct i on/ m
B sect i on
The st andar d condi t i on of C sect i on
The non- st andar d condi t i on of C sect i on
E sect i on
Figure14. Settlement curve of the typical cross-section after
construction
Nagaraj T
，
S M.K
，
Sridharam A
，
Incremental Loading Device for
Stress Path and Strength Testing of Soils
，
Geotechnical Testing
Journal
，
1981
，
4
（
2
）：
40-44
Zeng Guoxi, Pan Qiuyuan, Hu Yifeng. Research on the pit excavation
traits of soft clay foundation[J], Chinese Journal of Geotechnical
Engineering, 1988
，
10
（
3
）：
13-22
From the Figure 14, after construction the amount of base
recompression change is small, and after 3 years the maximum
recompression amount is 0.0407m. The largeest settlement
between each section is about 0.01m.
GUXing-wen, XUGuang-ming, CAI Zheng-yin, MI Zhan-kuan,LIU
Bin, LIU Jing-sheng. Research on Soft Ground Treatment of
Artificial Island by Means of Centrifugal Model Test[J], Journal of
Water Resources and Architectural Engineering, 2010.8
（
4
）：
126-130
KUANG Xilong, LI Zhen. A Dission on Structure Substituting
Technique in Geotechnical Engineering Eccentric Model test[J],
Technology ofHighway and Transpot, 2008.1
（
2
）：
5-8
