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NCMA Seismic Analysis with high PGA value

NCMA Seismic Analysis with high PGA value

NCMA Seismic Analysis with high PGA value

(OP)
If i input say 0.42 PGA value in NCMA design limits  max slope above wall (6H: 1V) when doing Seismic Analysis. .

The grading plan from which wall height is picked indicates a 3H: 1V slope above wall.

Increasing the wall height to match the limiting slope (6H: 1V) to satisfy Seismic analysis will require changing of grading drawings.

I have already used high friction values for infill,retained & foundation soils.

Is there any other way to get around.
 

RE: NCMA Seismic Analysis with high PGA value

Which version of the NCMA program are you using?  SRWall4 is the most recent version and may provide more latitude in the seismic analysis based on displacement Kh values and a different internal method. Be careful with your assumptions as this part is subject to many questions.

The Mononobe-Okabe equation solution used by NCMA does not work when PGA, back slope, and phi angle exceed the limits of the equation (square root of negative number for phi - backslope - aTan(Kh)).

That being said, high accelerations and steep slopes never solve very well by equation or slope stability analysis and require a more customized approach to the structure design. Displacement analysis, trial wedge analysis, and slope stability analysis are some of the tools used to analyze these conditions.

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