The soil being cohesive embankment fill (c â Ï soil), natural In some cases,įree-draining cohesionless soil may only be placed in the staticĪctive wedge (say at a 60 degrees angle) with the remainder of In practical situations cohesionless soil is unlikely to be pres-Įnt for a great distance behind a wall and encompass the entireĬritical failure wedge under seismic conditions. Have a backslope above the retaining wall, it is not uncommonįor the designers to compute what appear to be unrealistically Ground accelerations in excess of 0.3g and it is common to Many areas along the West Coast and Alaska involve peak ForĪ peak acceleration coefficient of 0.84, the active pressureīecomes infinite, implying a horizontal failure surface. Mic earth pressures due to the size of the failure wedge. Peak acceleration coefficient of 0.4 has a failure surface angle Sand of 40 degrees, a wall friction angle of 20 degrees, and a A horizontal backfill with a friction angle for Real solutions to the equation exist implying equilibrium is High pressures that asymptote to infinity at critical accelera. Tions or for steep backslopes, the equation leads to excessively The M-O equation is based on the Coulomb failure wedgeĪssumption and a cohesionless backfill. For the case of seismic active earth pressures, Result of basic assumptions used in the derivation of the M-O As noted in theĬommentary, these limitations in the M-O approach are the These concerns reflect the limitations of the M-O equationsĪs discussed in the Commentary within the NCHRP Projectġ2-49 Guidelines (NCHRP Report 472, 2002). Selected seismic coefficient cause the M-O equation toĭegenerate into an infinite earth pressure. ¢ How to use the M-O equations when high values of the The wall where an unrealistically large seismic active earth ¢ How to use the M-O equations for sloping ground behind Ï (friction angle of the soil), or where backfill conditions are Shear strength derived from both c (cohesion of the soil) and ¢ How to use the M-O equations for a backfill that is pre-ĭominantly clayey, for a soil involving a combination of The M-O equations for the determination of seismic earth The following problems are encountered when using Suggested as a standard method by Seed and Whitman (1970).Ī number of problems and related knowledge gaps with theĪbove approach have been identified, as discussed in the fol. Is still widely used in general geotechnical practice since being Ground acceleration coefficient at ground level. On the wall and backfill soil are computed from the peak In-place gravity walls or cast-in-place concrete cantilever orĬounterfort walls), where the maximum inertial forces acting ![]() Tional gravity or semi-gravity retaining walls (that is, cast. Pseudo-static seismic active earth pressures behind conven. M-O equations developed in the 1920s for determining System and the need to meet structural capacity requirements.Ĭurrent AASHTO Specifications use the well-established The constraints on deformation resulting from the structural Walls as well, though additional complexity is introduced from The discussions for gravityĪnd semi-gravity walls are generally relevant to these other ![]() Various other categories of walls exist, such as nongravity can. Gravity and semi-gravity walls, MSE walls, and soil nail walls. Ing walls focused on three primary types of retaining walls: The discussion of problems and knowledge gaps for retain. Tical problems and knowledge gaps commonly encounteredīy design engineers when conducting seismic design studies. ![]() As with the previousĬhapter, the primary focus of this effort was to identify prac. The final section provides key conclusionsĪbout knowledge gaps and problems. Retaining walls, slopes and embankments, and buried struc. The first three summarize knowledge gaps and problems for Knowledge gaps and problems is organized in four subsections. The Project Teamâs experience gained from conducting seismicĭesign studies for retaining walls, slopes and embankments, andīuried structures in seismically active areas. Was based on the Task 1 data collection and review, as well as Slopes and embankments, and buried structures. Gaps in current seismic analysis and design of retaining wall, Identify, illustrate, and document problems and knowledge ![]() The goal of Task 2 of the NCHRP 12-70 Project was to Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages. Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book.
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