Retaining Walls. Building walls retaining
Mixed Systems. When subsurface conditions
soil should be evaluated for the effects of seismic
vary significantly across a site, it is sometimes
earth pressures. The seismic earth pressure acting
on a building wall retaining nonsaturated, level soil
drilled piers and spread footings. Geotechnical
consultation is especially important for mixed
systems in order to control differential settlements.
The difference in lateral stiffnesses between the
∆p = 0.4khγ rw
spread footings and drilled piers must be considered
in the foundation earthquake design. Nominal values
of the soil springs, determined in accordance with
the requirements of this chapter, may be used in the
additional earth pressure due to
seismic shaking, which is assumed to be a uniform
kh = horizontal seismic coefficient in the
soil, which may be assumed equal to 0.5 SDS/2.5
Performance Objective 1A. The response
γ= the total unit weight of soil
modification factors, R, for Performance Objective
1A, shall be in accordance with the structural system
Hrw = the height of the retaining wall.
identified in Table 7-1. The design of the foundation
shall be in accordance with Chapter 7 of NEHRP as
The seismic earth pressure given above should be
modified by this chapter.
added to the static earth pressure to obtain the total
Enhanced Performance Objectives.
Equation 9-13 is a conservative approximation of the
(1) Linear elastic analyses with m factors.
pressures much higher than summarized above may
develop on walls that are required to develop passive
considered to be force-controlled, and their lower-
pressures to resist lateral forces. In such cases, static
bound capacity, QCL, will be the nominal capacity, in
passive earth pressure formulations, neglecting
accordance with FEMA 302, multiplied by the
inertia forces in the soil, may be used to estimate the
appropriate capacity reduction factor, N. If soil
magnitude of total (static plus seismic) earth
springs are used in the analyses, the nominal
pressures on the wall. A triangular pressure
stiffness coefficients prescribed in this chapter are to
distribution may be assumed.
be multiplied by 0.5 for Life Safety, 1.0 for Safe
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