Site Specific Earthquake Response Analysis, Case Study: Sebaou Valley-Algeria

Abstract eng:
A strong earthquake of magnitude Mw=6.8 struck Boumerdes, eastern Algiers region on May 21st 2003 at 7:44 pm (GMT+1). Many induced effects, mainly sand boiling and lateral spreading, have been observed. We perform in this work a site specific response analysis around the Sebaou Bridge, which suffered some damage. Geotechnical data of the site are gathered (borehole logs with SPT tests results as well as the physical properties of the soil). The ground accelerations recorded during this earthquake are used as bedrock motion which is analytically propagated upward through the soil profile to the free surface. An amplification factor ranging from 1.2 to 1.5 times the base rock acceleration is observed. On the other hand, liquefaction analysis is conducted and the factor of safety against liquefaction is determined for this site. Results give a safety factor less than unity. In order to quantify the liquefaction effect the liquefaction potential index PL is calculated and it is over 15 in all boreholes what indicates a high liquefaction potential. Also, induced effects due to liquefaction are evaluated and ground displacements (settlement and lateral spreading) are estimated.

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