Geology Reference
In-Depth Information
preventive measures. These might include compaction, grouting or the
installation of stone column drains that will help prevent excess pore
water pressure development, although they would not prevent settle-
ment. Alternatively, passive mitigation may be the best option
-
relo-
able soil. If
the ground does liquefy, then apart from movement of structures in or
on the ground, the settled soil might cause drag down (negative skin
friction) on any piles installed through that zone.
cate the proposed structures away from the zone of lique
For buildings such as one or two-storey houses, there are certain simple
rules that, if adopted, can reduce the risk of failure and would limit
injuries, especially in developing nations. These include ensuring that
walls are tied together, preferably by reinforced ground beams or
beams along the tops of walls (Coburn & Spence, 1992).
For larger engineered structures, these need to be designed to with-
stand the repeated force waves. As outlined in 6.10.1, given a parti-
cular design earthquake one can make estimates about the ground
motion characteristics that the structure will have to withstand. These
include peak acceleration, predominant frequency and duration of
shaking for a given return period earthquake. Typically, the return
period used is 1 in 500 to 1,000 years but the choice is rather arbitrary
and will depend on the nature and sensitivity of the project and the
seismic history. These bedrock ground motions may be modi
ed by
the local site geology or topography and estimates of the modi
ed
shaking characteristics can be made by dynamic analysis using
Figure 6.32
Responses of
buildings to
earthquake
shaking.
0.2s
0.4s
− Displacement of building (or
slope) depends on building form
and ground motion
− Buildings have natural
periods
− T = 0.1 N seconds
5
− If buildings RESONATE
motion is amplified
0.1
1.0
Ground Motion Period
Natural Period of Structure
10.0
Ratio
