Geoscience Reference
In-Depth Information
levels) were measured. The soil was compacted at a degree of compaction of 87%
such that the unit weight was 13.4 kN/m 3 .
The acceleration was applied through sweep sine wave and step wave at
different wall heights (Tables 1 and 2 ). The sweep test was used to determine the
resonance frequency of the wall. In the step tests, the acceleration was applied
through several steps but the increment was not reported. The Taft earthquake
record (EW component) was used as the input wave when the wall attained its
final height.
The wall was well instrumented (Fig. 1). The earth pressure transducers
were used at the bottom of the wall and the base of the backfill. The
accelerometers were installed in the backfill and on the reinforcement strips.
Tensile strains in the reinforcement layers and displacement in front of the wall
were also measured.
The “static” earth pressure recorded in the reinforcement was larger than
that predicted using the earth pressure theory, which could be attributed to
compaction effect (see Fig. 2a ). With the shaking, the earth pressure increased
following an increase in the input acceleration (Fig. 2b).
The resonant frequencies of the wall at different heights are shown in
Fig. 3a . It is seen that the resonant frequency reduced with the increase in height,
and it was 3.5 Hz at the full height of 6m. Significant phase difference between
acceleration at resonance, as large as 7, was seen between the bottom and surface
of the backfill as the base acceleration exceeded 150 gal.
An identical acceleration response was recorded in the backfill and in the
reinforcement. Note, however, that the accelerations were inside the reinforced
zone. During shaking, the vertical stress at the bottom of the backfill increased.
The acceleration amplification of the wall during shaking is shown in Fig. 3b. The
accelerations in the backfill, concrete facing, and the reinforcement were slightly
different, but all amplified toward the surface of the backfill. The amplification
ratio was greater than 3 when the input acceleration exceeded 150 gal (0.15 g).
Table 1 Input Acceleration During Testing for Reinforced Soil Wall
Wall Height
(m)
Step test *
Sweep test
Input earthquake
2.5
0.5-8 Hz (49 gal)
2 Hz (35-145 gal)
-
3.5
0.5-10 Hz (38 gal)
2 Hz (42-145 gal)
-
4.5
1.0-10 Hz (46 gal)
2 Hz (67-203 gal)
-
6.0
1.0-10 Hz (46 gal)
2.3 Hz (35-178 gal)
Taft (EW), 112-220 gal
Source: Futaki et al., 1996.
*No information given about the increment of acceleration.
Search WWH ::




Custom Search