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GSP 131 Contemporary Issues in Foundation Engineering

test results, design calculations). Where this is considered, soil-structure interaction analyses will need to be performed.

5.6.3Liquefaction. In many earthquakes where liquefaction occurs, the soil may not liquefy until the end of the earthquake. Therefore, piles in liquefied ground may still

be able to rely on zone during the liquefaction will

the vertical and lateral support of the soil in the potentially liquefied

earthquake.

However, due

occur,

it

seems

prudent

to

to uncertainties assign a reduced

as to exactly

when

vertical and

lateral

resistance to potentially liquefiable soil surrounding a function as a load carrying member during and after an by Ishihara and Cubrinovski (1998) suggest that the

pile if the pile is expected to earthquake. Results presented lateral resistance of a pile in

liquefied liquefied

ground is ground.

approximately 0.1 to 1.0 percent of the lateral Therefore, if a pile foundation in potentially

resistance in non- liquefiable soil is

expected to be required particularly

carry lateral loads after the surrounding soil liquefies, inclined to provide adequate lateral support. This reduction in lateral important for relatively flexible micropiles.

piles may support is

Studies reported in the FOREVER (2003) project showed that vertical micropiles were not effective in reducing liquefaction. Inclined micropiles, however, were shown to limit seismically-induced soil movements (and pore pressure buildup) resulting in no liquefaction in the zone affected by the piles, whereas the free-field soil did undergo liquefaction. If inclined piles are used, the pile cap connections should be designed to sustain moment loads induced by lateral movements and the inclined piles should be designed to sustain lateral loads due to soil settlement.

Final Remarks

This paper provides a brief overview of the many and varied aspects of Case 1 micropile design. It is hoped that the teaching of the manual from which this paper is drawn will help the various code recommendations and proposals become “state of practice” and that owners and contractors alike can progress on common and acceptable ground.

REFERENCES

AASHTO (1988), “Manual on Subsurface Investigations”, American Association of State

AASHTO (2002), “Standard Specifications for Highway Bridges”, Association of State Highway and Transportation Officials Publication, Washington, D.C., ISBN: 156051-171-0.

Bjerrum, L., “Norwegian experiences with steel piles to rock,” Geotechnique, Vol. 7, pp. 73-96, 1957.

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