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31 the development of a screening method was the identifica- Validation of design charts by numerical analysis. tion of potentially liquefiable soils and how these condi- Apply procedures to an established range of problems. tions would be handled in the evaluation. Guidelines were Develop screening guidelines to provide a basis for screen- developed for the NCHRP 12-49 Project for treating the ing culverts and pipelines relative to their need for fur- stability of approach fills located on liquefiable soils; these ther seismic evaluation (that is, define the "no-analysis methods served as a starting point for this Project as well. required" criteria). · As no LRFD approach for the static design of slopes exists, a · Identify analysis procedures for peak ground displacement. commentary that addressed strength parameter selection for Guidelines on the selection of design peak ground dis- static and seismic design and was consistent with approaches placement parameters (for example, spatial distribution to retaining wall design was developed as part of this Project. of ground motions and soil stiffness parameters). Effects of soil slope slumping, liquefaction-induced lat- Based on the literature review and identification of eral spread and settlements, and fault rupture. knowledge gaps summarized in Chapters 2 and 3, the work on slopes and embankments was limited to soil conditions 4.4.1 Analysis Procedures for TGD and did not include rock slopes. The stability of rock slopes during seismic loading is controlled by the specific fracturing The response of a buried linear structure can be described patterns of the rock, making a generic approach for the eval- in three principal types of deformations: (a) axial deforma- uation of the seismic stability of rock slopes beyond what tions, (b) curvature deformations, and (c) ovaling (for circu- could be accomplished by this Project. For this reason it was lar cross section) or racking (for rectangular cross section) concluded that the topic of rock slope stability during seismic deformations as shown in Figures 4-5 and 4-6. loading should be addressed by site-specific evaluations. The axial and curvature deformations are induced by com- ponents of seismic waves that propagate along the culvert/ pipe axis. Current design and analysis methodologies for 4.4 Developments for pipelines and tunnel systems were developed typically for Buried Structures long, linear structures. Culverts and pipe structures for trans- portation applications, however, are typically of limited length. The final area of development involved a methodology for For this condition the transient axial/curvature deformations dealing with buried culverts and pipe structures. It was rec- should generally have little adverse effects on culvert/pipe ognized that the seismic hazard to buried culverts and pipes structures and, therefore, design and analysis provisions may can be classified as being caused by either peak ground dis- not be required for these two modes of TGD effects. This pre- placement or TGD resulting from wave propagation. How- liminary assumption, however, was further evaluated during ever, there was no existing seismic design methodology or the completion of the initial phase of this study and verified guidelines for the design of culvert or pipe structures in Sec- by numerical analysis. tion 12 of the AASHTO LRFD Bridge Design Specifications. The ovaling/racking deformations are induced along the Design and analysis procedures have been proposed by transverse cross section when seismic waves propagate per- some researchers and design engineers for pipelines (for ex- pendicularly to the culvert/pipe axis. The design and analysis ample, gas and water) or tunnel (that is, transportation or water) methodology develop by Wang (1993) can be readily applied systems. While some of these procedures can be used for the for culverts with circular or rectangular cross sections. For design and analysis of culvert and pipes (for example, the trans- example, the simple design chart shown in Figure 4-7 allows verse racking/ovaling deformation of the section), others quick determinations of induced culvert/pipe racking/ovaling cannot be directly applied because (1) culverts and pipes are deformations. typically of limited length, (2) culverts and pipe structures Previous observations have suggested that smaller diameter are typically constructed within a built-up embankment, and pipes (or small diameter highway culverts) are more resistant (3) the characteristics of peak ground displacement and its to ovaling deformations than the larger culvert structures. effects on culvert and pipes are phenomenologically complex. A further investigation of the factors resulting in this differ- The analytical methodology development for buried struc- ent performance between large and small buried structures tures involved the following main elements: was evaluated. Once identified, these factors were reflected in the screening guidelines discussed above. In addition, the · Develop analysis procedures for TGD. proposed analytical methodology development attempted Guidelines on the selection of design TGD parameters. to identify simplified procedures for noncircular and non- Methods for estimating transverse racking/ovaling rectangular sections. It was anticipated that parametric numer- deformations (provide design charts as well as recom- ical analyses would be required for developing these simplified mended step-by-step procedure). procedures.
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32 MBF Figure 4-5. Axial/curvature deformations. Another important aspect for evaluating the TGD effects duced during ground shaking. This is particularly important on culvert/pipe structures was to determine the appropriate because given the same PGA value, the anticipated PGV for design ground motion parameters to characterize the ground CEUS would typically be much smaller than that for the WUS. motion effects. It has long been recognized that PGA is not a Results based on the PGA versus PGV study presented earlier good parameter for buried underground structures. Instead, in the work plan for the retaining walls, slopes, and embank- PGV is a good indicator for ground deformations (strains) in- ments were used for the culvert structures. Figure 4-6. Ovaling/racking deformations.