| dc.description.abstract | Shield tunneling is being carried out ever more frequently for tunnel
construction in soft ground. During excavation, the face stability analysis
of a shallow tunnel is a complex three-dimensional problem. Therefore, a
series of single tunnel centrifuge models embedded in soft soils was used
to investigate the distributions of surface settlement troughs, the changes
of pore water pressure and the collapse mechanisms around the tunnel.
The clay beds were consolidated in a rectangular consolidometer.
Then the clay bed was reconsolidated in a centrifugal acceleration of
100g. A horizontal hole with 6cm in diameter was carefully cut and a
model liner with 6cm in diameter was carefully put inside the hole in 1g
to model a liner. The model tested in a centrifuge gravity field of 100g
can model a prototype tunnel with 6m in diameter. The tunnel was not
penetrated through the whole clay bed in order to simulate a threedimensional
problem. After centrifuge acceleration was increased to 100g,
the tunnel collapse tests were performed by gradually reducing the air
pressure. Model tests with different cover-to-diameter ratio (C/D) and
unlined length-to-diameter ratio (P/D) were conducted to investigate the
face stability during tunneling in soft ground.
For the tunnel having the same cover, the test results show that
collapse (OF)c decreases and maximum surface settlement ( max d )
increases with increasing of the unlined length. If the P/D ratio is less
than or equal to 0.5, the measured max d increases as the C/D ratio
潛盾隧道開挖面穩定分析
-IVincreases.
On the other hand, if the P/D ratio is large than or equal to 1.5,
the measured max d decreases as the C/D ratio increases. The values of
max d obtained from plane strain tests (P/D=¥) are larger than those
obtained from 3D tests (P/D=0,0.5,1.5). For the same P/D ratio, the width
of settlement trough increases as the C/D ratio increases. For the same
C/D ratio, the horizontal displacement of the tunnel face becomes larger
when the P/D ratio is greater. If the shear strength (Su) of soil in the field
is known, designers can estimate the possible supporting pressure at
collapse. | en_US |