Assessing and managing the risk of earthquake-induced liquefaction to civil infrastructure - Seismic Risk Analysis and Management of Civil Infrastructure Systems - page 122

liquefaction. More recently, Shamoto et al. (1997, 1998) and Wu & Seed
(2004) also proposed charts for estimating cyclically induced reconsolida-
tion volumetric strains based on laboratory data, but their charts have not
been used as widely as those by Tokimatsu & Seed (1987) and Ishihara &
Yoshimine (1992). A comprehensive review of the available methods can
be found in Cetin et al. (2009a,b). Furthermore, based on the work of
Ishihara & Yoshimine (1992) and Zhang et al. (2002), Idriss & Boulanger
(2008) proposed empirical charts which relate the post-liquefaction volu-
metric strain with the normalised CPT tip resistance. Even without signifi -
cant settlement due to volumetric strains, the reduction in shear strength
resulting from liquefaction can cause a bearing capacity failure, where the
underlying soil no longer has suffi cient residual strength to support the
building loads (see Section 5.4.3).
5.3.5 Likelihood of PGD
A risk-based approach should consider the probability of different modes
of ground deformation occurring, and then evaluate the probability of
exceeding defi ned amounts of settlement or lateral movement. Based on
the ideas of Kramer & Mayfi eld (2007), as discussed in Section 5.2.2,
Juang et al. (2010) noted that their framework for assessing the conditional
probability of liquefaction as a function of peak ground acceleration and
magnitude values could be extended to evaluate the probability of exceed-
ing a prescribed liquefaction-induced lateral spreading displacement or
settlement.
Using a probabilistic approach for such calculations becomes computa-
tionally complex, where the joint probability distributions of a number of
dependent and independent variables need to be considered. In practice,
for a linear infrastructure system extending over a signifi cant distance, it is
unlikely that a full probabilistic analysis would be feasible. However, the
elements of the framework presented by Juang et al. (2010) should all be
considered for a quantitative assessment of the potential risk to an infra-
structure system due to liquefaction-induced ground deformation. These
elements are shown in the left hand boxes in Fig. 5.4. Various input data are
required to undertake this type of assessment. The assessment framework
shown in Fig. 5.4 requires a signifi cant degree of engineering judgement; it
is the authors' view that pure statistical approaches are not appropriate in
the context of this chapter.
Qualitative estimates of probability are commonly expressed using a fi ve-
point scale similar to that shown in Table 5.1. Where engineering judgement
is heavily relied upon for an assessment of risk, it is important to defi ne the
scales in order to provide consistency.