1. Evaluate the fundamental frequency/l of the backfill for the design
earthquake using one-dimensional amplification theory, and estimate the
dominant frequency, /, of the expected ground motion.
2. If f/fl is less than 0.25, neglect the amplification of ground motion.
If f/fl is in the vicinity of 0.5, increase the peak acceleration, A, and the
peak velocity, V, of the design earthquake by 25%-30%. The smaller
number should be used for small values of N/A, and the larger number
for large values of N/A. If f/fl is between 0.7 and 1, increase A and V
by 50%.
3. Use the values of A and V from the previous step in a design procedure
that is based on a rigid-plastic model (e.g., the R-E method or
the Wong method).
The fundamental frequency /l = VJAH, where Vs
is the shear wave
velocity, for backfills will typically be 5 Hz-15 Hz. Dominant frequencies
of ground motions range generally from 2 Hz-5 Hz. Thus, the most typical
range of f/fl is 0.2 to 0.6.