Geoscience Reference
In-Depth Information
Fig. 4.8. Microzonation withrespect toground shaking intensity (Ansal et al., 2005a)
Liquefaction susceptibility microzonation maps were also produced for the five munici-
palitiesintheMarmararegion(Erdiketal.,2005;Ansaletal.,2006b)tobeusedforurban
planning. The local soil stratifications and soil characteristics were determined based on
previouslyandrecentlyconductedsoilborings.Theinvestigatedregionsweredividedby
gridsystemswithcellsizeof250m
500mdependingontheavailable
borings and other relevant information(Ansal et al., 2005b).
×
250mor500m
×
The liquefaction susceptibility is based on the calculation of the safety factors along
the top 20m depth for each soil profile for all liquefiable soil layers according to Youd
et al. (2001) based on the available SPT-N blow counts and using the average peak
ground accelerations calculated from site response analyses. The liquefaction potential
(“liquefaction potential index”, PL) for each borehole was determined according to
Iwasaki et al. (1982).
Two variables are required for the assessment of liquefaction susceptibility: (1) seismic
demandonthesoillayers,expressedintermsofcyclicstressratio,CSR;and(2)capacity
ofthesoillayerstoresistliquefaction,expressedintermsofcyclicresistanceratio,CRR.
The oldest and still the most widely used approach as summarised by Youd et al. (2001)
is the simplified procedure for assessing liquefaction susceptibility originally proposed
bySeedandIdriss(1971)basedonSPT-Nvaluesandcyclicstressratiocalculatedusing
stress reduction factor. The cyclic stressratio,CSR, is expressed as
=
τ
av
65
a
max
g
σ
v
CSR
σ
v
=
0
.
r
d
(4.1)
σ
v
