Basic Geotechnical Earthquake Phần 6 pdf

70 Basic Geotechnical Earthquake Engineering

Fig. 6.10 Plot used to determine cyclic resistance ratio for clean and silty sands for

M = 7.5 earthquake (Courtesy: Day, 2002)

Table 6.1 Magnitude scaling factors (Courtesy: Day, 2002)

Anticipated earthquake magnitude Magnitude scaling factor

8.5 0.89

7.5 1.00

6.75 1.13

6 1.32

5.25 1.50

Factor of safety against Liquefaction: Factor of safety (FS) against liquefaction is

defined as: FS = CRR/CSR. If the cyclic stress ratio caused by anticipated earthquake is

greater than cyclic resistance ratio of in-situ soil, liquefaction could occur during earthquake.

Liquefaction will not take place otherwise. Higher the factor of safety, more is the resistance

of soil against liquefaction during earthquake. Soil having factor of safety slightly greater than

one can also liquefy. For example if lower layer liquefies, then upward water flow could

induce liquefaction of upper layer as well. This layer has factor of safety against liquefaction

slightly greater than one.

However, in the above analysis, there are lot of corrections. These corrections are

applied both to cyclic stress ratio as well as to cyclic resistance ratio. This is done for more

accurate analysis. Otherwise the entire analysis is only gross approximation. Consequently,