Creep behavior of soil nail walls in high plasticity index (PI) soils : project summary.
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2015-08-31
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Abstract:Soil nailing is a convenient and economic
stabilization method for the reinforcement of existing
excavations by installing threaded steel bars into cuts
or slopes as wall construction progresses from top
down (Figure 1). An aspect of particular concern in
the soil nail wall guideline is the creep behavior of
this type of system in high-plasticity (HP) clays (i.e.,
those soils with a plasticity index greater than 20).
However, soil nail walls have been constructed with
success in HP soils (particularly in Texas), and no
issues associated with creep behavior have been
observed so far, including walls that were built more
than 20 years ago. The main motivation of this
research project is to gain a better understanding of
the behavior of soil nail walls in HP clays and to
suggest possible modification to the current
guideline.
In order to assess the effect of creep behavior in HP
clays, the following tasks were conducted:
1. Pullout tests on eight existing anchors installed in
1991 at the clay site at the National Geotechnical
Experimentation Site at Texas A&M University
(NGES-TAMU) were performed to explore any
effect on the bond strength related to long-term
installation (i.e., soil ageing).
2. Pullout tests on 16 new vertical soil nails
installed at the NGES-TAMU clay site were
carried out following different protocols to learn
about the effect of stress level on creep behavior.
3. Pullout tests on six new sacrificial nails installed
at different heights in a new soil nail wall at
Beaumont were carried out to learn about the
nail creep behavior under actual conditions.
4. The actual soil nail wall was monitored at
Beaumont (453 ft. long and 25 ft. high) for
13 months to learn about the service load in nails
and different wall movements in time.
5. Laboratory tests (e.g., triaxial creep and
oedometer tests) were performed on samples
gathered from the two sites investigated in this
project (i.e., NGES-TAMU and Beaumont).
6. Numerical simulations were conducted using
FLAC-3D. All components of the soil nail wall
were simulated. The simulations were first
calibrated against the pull-out tests and lab data.
Then the Beaumont soil nail wall was modeled,
and a parametric study was performed.
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