Retaining Wall Backfill Pressures Due To Seismic Forces

[charlierock]

I am a soils engineer who has never worked in a seismic zone 4 before. I now have a project in zone 4 which has some retaining walls to 10 feet high. For granular retaining wall backfill, I generally give an active pressure value of 30 pcf for level backfill and increase that value for sloping backfill. Will these pressures increase during a seismic event and how do I calculate the new pressures due to the seismic load?

 

[dimitrios]

Dear charlierock
in the particular region you work with seismic activity, there must exist a code to apply, that specifies how to treat the problem (if I understood it correctly).
From my experience in Greece, where we have seismic activity, retaining walls are divided in walls that can move or deform and walls that are not allowed to move2.
For the first case it is suggested to use the Mononobe-Okabe method with extra horizontal action ah*W and verical
-av*W
W: weight of critical soil prism

ah=a/(q*g): multiplier of acceleration of gravity increase in the horizontal direction
a: surface acceleration given for each zone of seismic activity by the seismic code
q: factor for wall behaviour (2 for large movement allowed, 1.2 for flexible wall with anchors or on rock, 1 for stiff wall on rock or piles and 0.7 for braced wall)
g: acceleration of gravity
av: respectively in the vertical direction)taken as av=0.3*ah.

For the second case only pressure at rest is considered, which is increased by a trapezoidal diagramm with values 1.5*a*gamma*H at the surface, down to 0.5*a*gamma*H at the foot of the wall
a: as above
gamma:specific weight of soil
H: height of wall with maximum value for diagramma calculations H=<10m

(Now that I look what I have written I understand that I have been carried away and written things that are already well known and propably useless, but the guys in the Forum are very kind and will forgive this miserable lecture-like reply)

Regards

 

[Focht3]

Thread 88831-255 is an identical post in the Earth Retention Engineering Forum (which is also a part of the Geotechnical Engineering area of [green]Eng-Tips[/green].)

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http://www.eng-tips.com/viewthread.cfm?SQID=88831&SPID=255&newpid=255&page=1

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