Civil Engineering Reference
In-Depth Information
10.5.3 Dynamic analysis
deformations resulting from seismic excitation to
be computed.
Both finite-element and finite-difference
approaches can be used to compute permanent
deformations. Typical analyses involve applica-
tion of a seismic record to the base of a model
and propagating the wave through the model.
Small amounts of damping are sometimes applied
to account for real energy losses that are not
represented by either the joint behavior or the
rock mass behavior.
Although there are no documented cases of
large-scale failures of open pits under seismic
loads, there are many instances of failure of nat-
ural slopes during earthquakes (see Section 6.5.1).
In open pits, smaller-scale failures comprising
rock fall and bench-scale structurally controlled
failures may occur under severe shaking. Where
such failures are an operational hazard, mitig-
ation can usually be provided by suitable catch
bench configurations.
Traditional approaches to dynamic analysis are
based on a pseudo-static approach in which
the effects of an earthquake are represented
by constant horizontal and/or vertical accelera-
tions. The first explicit application of the pseudo-
static approach to the seismic slope stability has
been attributed to Terzaghi (1950). The applic-
ation of horizontal and/or vertical accelerations
can be made in limit equilibrium methods and
numerical methods alike. The results of pseudo-
static analyses depend on the value of the seis-
mic coefficient as discussed in Section 6.5.4.
Difficulty in assigning appropriate pseudo-static
coefficients and in interpretation of pseudo-
static safety factors, coupled with the advance
of numerical models has provided an alternat-
ive to the use of the pseudo-static approach
for seismic slope stability analyses. Numerical
methods, in addition to the Newmark method
discussed in Section 6.5.5, allow permanent slope
