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Figure 4.5: (a) Relationship between Thickness of Liquefiable Layer and Thickness of Overlying
Layer at Sites for which Surface Manifestation of Liquefaction has been Observed, and
(b) Guides to Evaluation of Respective Layer Thicknesses (after Ishihara 1985)
Lateral spreads involve displacement of larger blocks of soil as a result of liquefaction in a
subsurface layer. Movements occur in response to the combined gravitational and inertial forces
generated by the earthquake. Lateral spreads generally develop on gentle slopes (usually less
than 6%) and move towards a free face, such as an incised river channel. Horizontal
displacements on lateral spreads commonly range up to several meters, but can extend up to
several tens of meters where slopes are particularly favorable and ground shaking durations are
long. Lateral spreads disrupt foundations and utilities that are located on or across the failure.
The compression of structures, such as bridges crossing the toe of the failure, has been noted.
The damaging affects of lateral spreading on bridges were illustrated in Chapter 2. Procedures
for the evaluation and prediction of lateral deformations are presented in Section 4.4.
4.3.3 Excessive Deformation of Retaining Structures and Abutments
Liquefaction can cause excessive displacements of bridge abutments and wing walls. The
mechanisms by which liquefaction threatens walls and retaining structures are discussed below.
1. Loss of soil strength resulting in increased active earth pressures acting against the
inboard sides of the walls or retaining structures. This results in failure or excessive
deformation by:
a. lateral translation,
b. rotational failure or overturning,
c. structural failure of the retaining system,
d. failure or breakage of anchors or ties, and
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