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The relationship shown in Figure 4.14 was developed for clean sands and for magnitude 7.5
earthquakes. For soils with more than 5% fines content, the representative (N 1 ) 60 values should
be increased slightly using the correction factors recommended in the summary report by Youd
and Idriss (1997). For earthquakes of magnitude other than 7.5, the CSR eq values should be
scaled using the MSF defined in Chapter 3.
CSR
av
σ '
o
Figure 4.14: Chart for Estimation of Volumetric Strain in Saturated Sands from Cyclic Stress Ratio
and Standard Penetration Resistance (Tokimatsu and Seed 1987)
It is recommended that both procedures be used to estimate the likely range of settlement
associated with cyclic loading of sandy soils.
4.7 LATERAL SPREADING AND PILE FOUNDATION RESPONSE:
DESIGN CONSIDERATIONS
Pile foundations are commonly employed for bridges, abutments, and approach structures.
Therefore, it is important to understand how they will perform in the presence of liquefaction and
lateral soil deformation. For flat sites away from free-face conditions, lateral soil deformation is
usually not a concern. The presence of highway embankments or abutments will impose static
shear stresses in the soil that can result in lateral deformations. Liquefaction-induced settlement
of competent soil underlain by liquefiable soils may impart downdrag loads on piles. This could
potentially affect friction piles and partially end-bearing piles; however, this behavior has not
been demonstrated to be a problem in recent earthquakes. As described in Chapter 2, bridges
located on flat ground and supported by end bearing piles have generally performed well. Older
bridges with friction piles should, however, be re-evaluated for the possibility of excessive
vertical displacements.
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