Seismic Analysis and Design of Retaining Walls, Buried Structures, Slopes, and Embankments (2008) / Chapter Skim
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Pages 18-25
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From page 18... ...
For the case of seismic active earth pressures, the M-O equation is based on the Coulomb failure wedge assumption and a cohesionless backfill. For high accelerations or for steep backslopes, the equation leads to excessively high pressures that asymptote to infinity at critical acceleraC H A P T E R 3 Problems and Knowledge Gaps
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From page 19... ...
A horizontal backfill with a friction angle for sand of 40 degrees, a wall friction angle of 20 degrees, and a peak acceleration coefficient of 0.4 has a failure surface angle of 20 degrees to the horizontal. It will lead to very large seismic earth pressures due to the size of the failure wedge.
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From page 20... ...
Wall flexibility also could influence the nature of soil-wall interaction. A number of finite element or finite difference numerical response analyses have been published in recent years, modeling the dynamic earthquake response of cantilever walls.
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From page 21... ...
The combination of large PGA and very high wall height poses questions as to the appropriate seismic coefficient to use for design. Whereas model studies using centrifuge or large shaking tables, together with numerical analyses using finite element of finite difference programs, are providing insight on the complex physical behavior of MSE walls under seismic loading, current practical design approaches described in the literature rely on pseudo-static, limit-equilibrium analyses, such as those used for conventional gravity walls.
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From page 22... ...
In addition, the limitations and problems with the use of the M-O equations for external stability assessments are similar to those previously described for conventional semigravity retaining walls, and along with performance criteria based on allowable wall displacements, can be addressed in a similar manner to approaches described for semi-gravity walls. As discussed in the next chapter, studies related to wall height/stiffness and ground motion dependent seismic coefficients for design, along with improved approaches for evaluation of internal and external seismic stability, are clearly needed.
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From page 23... ...
For the wedge failure, three-dimensional limit equilibrium wedge analyses using stereographic projection of joints and open free surface orientations are used for gravity loading. While the consideration of seismic loads in terms of pseudo-static acceleration can readily be implemented for the plane failure which can be carried out with most two-dimensional slope stability programs, a wedge failure under seismic excitation is not widely analyzed.
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From page 24... ...
There was a lack of data of how to determine the appropriate TGD parameters for culverts and pipes embedded in embankments, especially in high embankments. • The effect of soil overburden thickness (or embedment depth)
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From page 25... ...
• Buried structures – Simple-to-use design charts for medium-to-large-size culverts and pipes under the effect of transverse seismic racking deformations, taking into account soil-structure interaction effect. – Guidance on how to select transient ground deformation (or strain)
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