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dewatering may be warranted. Additionally, structural retrofit and hardening also may be
required.
9.2 GENERAL RECOMMENDATIONS FOR FUTURE WORK
1. The influence of pile groups on lateral ground deformation is poorly understood. In
current practice, it is conservatively assumed that piles offer no lateral resistance to
ground movement (free-field ground deformations are assumed). In light of the case
studies reviewed, this is a prudent assumption for small pile groups. Field observations
confirm that large pile groups can withstand lateral earth pressures due to movement of
liquefiable soil and overlying “crusts” of competent soil. This issue is relevant for
assessing the seismic performance of existing bridge foundations and the prioritization
for remedial ground treatment given the number of bridges involved and the limited
resources that are available for seismic rehabilitation.
2. The seismic performance of batter piles has been shown to be quite poor at sites
exhibiting lateral ground deformation in excess of 0.15 to 0.3 m (0.5 to 1 ft). The
performance of bridge abutments supported by batter piles should be reviewed.
3. The seismic performance of embankments with various soil improvement strategies
(vibro-compaction, soil mixing, deep dynamic compaction) should be evaluated.
4. Recent investigations employing physical model testing (centrifuge, shake table) have
been fruitful for augmenting the database of well documented case studies, the validation
of numerical models, and for evaluating the effectiveness of soil improvement adjacent to
bridge embankments and slopes. Continued work incorporating pile foundations is
recommended.
5. The influence of long-duration motions, such as those associated with great Cascadia
Subduction Zone earthquakes, on the performance of highway embankments and bridge
components should be investigated.
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