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PRACTICAL RECOMMENDATIONS FOR EVALUATION AND MITIGATION OF SOIL LIQUEFACTION IN ARKANSAS | ||||
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Brady Cox, Ph.D.
July 1, 2009 - June 30, 2010
Only a few states in the nation have areas with higher earthquake design ground motions than
Northeast Arkansas. The seismic hazard in this portion of the country is governed by the potential for
large earthquakes within the New Madrid Seismic Zone (NMSZ). It is well know that large earthquakes
have historically caused significant damage to bridges. Much of this damage has been attributed to
liquefaction of foundation soils, leading to major displacements of abutments and piers. The recently
released AASHTO Guide Specifications for LRFD Seismic Bridge Design (2009) require liquefaction
assessment in much of Northeast Arkansas, and recommend assessment in an even larger portion of the
state. Designing bridge foundations in Arkansas against the effects of earthquake-induced soil
liquefaction has become increasingly expensive over the past few years. The uncertainty involved with
developing a safe, yet economical design is greater in Arkansas than in most other parts of the country
due to the presence of deep, loose, sandy soil deposits found within the Mississippi embayment. Soil
deposits are routinely encountered at bridge sites in Northeast Arkansas that appear to be loose enough to
liquefy down to at least 100 feet deep (based on empirical SPT liquefaction triggering procedures).
However, the current state-of-practice for evaluating soil liquefaction using simplified empirical methods
does not strictly apply to soil deposits greater than about 65-75 feet deep (AASHTO 2009, Idriss and
Boulanger 2008). While it is understood that the extrapolation of simplified liquefaction triggering
methods to these depths is of uncertain validity, the designer must do something reasonable to try and
predict the susceptibility of these deep, loose soils to liquefaction.
The objectives of this research are to develop practical recommendations for evaluation and
mitigation of soil liquefaction in Arkansas. This research is primarily aimed at aiding AHTD, and other
engineers, in the design of bridge foundations in the high-seismicity areas of Northeast Arkansas.
Recommendations set forth in the recently released AASHTO Guide Specifications for LRFD Seismic
Bridge Design (2009) will be incorporated into the research. Furthermore, recent improvements in
liquefaction assessment not contained in AASHTO (2009) will also be considered (i.e. Idriss and
Boulanger 2008). Specifically, objectives of this research include: (1) A thorough review of the
procedures typically used to evaluate liquefaction in Arkansas, (2) Refinement of these procedures and
development of easy-to-use spreadsheets for SPT-based liquefaction triggering analyses, (3)
Recommendations for the liquefied shear strength (i.e. residual shear strength) of soils for use in postliquefaction
evaluation of pile foundations, and (4) Investigations into potential soil improvement
techniques that might be used to mitigate against deep soil liquefaction.
TRB Keywords: Liquefaction, earthquakes, piles
Product: In Progress (MBTC DOT - 3017)
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