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Figure 4-7. Earthquake-induced structural transient
racking/ovaling deformations.
As a final consideration, there is an on-going proposal In general, there are three major steps for evaluating the
(NCHRP Project 15-28) to upgrade the computer program PGD effects: (1) determine the PGD patterns (that is, spa-
CANDE-89 to incorporate the LRFD design methodology. tial distributions) using the site-specific subsurface condi-
CANDE-89 is a comprehensive design/analysis tool for the tions encountered at the culvert location; (2) derive the
cross section design and analysis (in two-dimensional plane- suitable soil stiffness accounting for the dynamic as well as
strain domain) of buried structures, particularly culverts. The cyclic effects (for example, softening due to liquefaction and
seismic effects of transient racking/ovaling deformations on repeated loading cycles; and hardening due to increased
culverts and pipe structures must be considered additional to strain rates); and (3) evaluate the structural response to the
the normal load effects and preferably could be incorporated PGD taking into consideration soil-structure interaction
into the updated CANDE analysis. In Chapter 10 recom- effects.
mendations on proposed seismic design methodologies to be In estimating the PGD patterns for liquefaction-induced
incorporated into the CANDE program are made. It is antic- lateral spread, slopes/embankment slumping, and post-
ipated that an option would be required in the CANDE pro- liquefaction settlements, the procedures developed for re-
gram to allow ground displacement profile as a loading input taining walls, slopes, and embankments can be used. Fault
to the CANDE analysis. rupture has a relatively low occurrence frequency. It is gen-
erally difficult to design for the effects of fault rupture unless
4.4.2 Analysis Procedures for Permanent the fault displacement is small or the backfill within the soil
Ground Deformations (PGD) envelope consists primarily of properly designed compress-
ible material to accommodate the fault displacement. As
Various approaches for analysis or design of pipeline sys- part of this study, general guidelines on design strategy for
tems (for gas and water) have been proposed under the effect of coping with large PGD, based on various previous project
PGD including those to account for the effects of liquefaction- experiences gained from tunnel and pipeline design, were
induced lateral spread, slope deformations (slump), post- identified.
liquefaction settlements, and fault displacements. Significant
disparity exists among these approaches. There are also dif-
4.5 Summary
ferent performance requirements and loading criteria being
used or proposed for different studies. A consistent method- In summary, the proposed analytical methodology devel-
ology and design criteria compatible with other components opment plan resulted in work product elements shown in
of the highway facilities are yet to be developed for the culvert Table 4-1. This summary is a modified version of Exhibit 6 of
and pipe structures. the Working Plan for the NCHRP 12-70 Project.
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Table 4-1. Work product elements.
Type of Investigation Purpose
Establish Basis for Determining Identifies consistent approach for defining ground motions to use for
Ground Motions Suitable for CEUS seismic evaluation of retaining walls, slopes and embankments, and
and WUS buried structures, including modifications that account for permanent
displacements.
Develop Design Charts for Estimating Provides a rational basis for selecting seismic coefficient as
Height-Dependent Seismic a function of both wall height and slope height for different soil
Coefficient conditions.
Update Design Charts for Estimating Provides end users the means of estimating slope and wall
Slope and Wall Movement movements as a function of yield acceleration, PGA, and PGV.
Displacements
Evaluate Suitability of Limit Offers end users the means for improved methodology for
Equilibrium Computer Program based establishing design seismic earth pressure magnitudes for mixed soil
on Method of Slices for Determination conditions, steep backslopes, and high ground motions.
of Lateral Earth Pressures
Identify Method for Designing Establishes a basis for estimating seismic earth pressures to use for
Nongravity Cantilever Walls and wall design and provides a simplified approach for conducting
Anchored Walls Using Limit displacement-based analyses.
Equilibrium and Displacement-Based
Methods
Review Basis for Estimating Seismic Proposes revisions to design methodology based on conclusions
Performance of MSE Walls from evaluations carried out for this Project, as appropriate.
Document Approach for Evaluating Provides documentation for limit equilibrium and displacement-based
Seismic Stability of Slopes and approach for evaluating seismic stability of slopes.
Embankments
Develop Design Approaches for Provides design guidance and specifications.
Permanent and Transient Ground
Deformation for Culverts and
Pipelines
