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33 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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34 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