Determination Difficulties of Cyclic Strains of Soil During Earthquake

Estimation of the seismic response of shallow foundations during a strong earthquake has been proven a difficult task throughout the years. The main cause of this difficulty arises from the fact that soil behaves in a highly non-linear manner when subjected to large cyclic strains. 


It can deform substantially and, when saturated, can develop high pore pressures and finally liquefy. Liquefaction consequently leads to severe loss of bearing capacity, which damages seriously the superstructure. Extensive damage  to  shallow  foundations  due  to  liquefaction  has  been  reported  in numerous cases in the past, from Niigata (1964) earthquake to the more recent 1999 M 7.4 Kocaeli earthquake. 
 

Despite the severity of damages, relatively little has been achieved towards the development of a consistent methodology for the design of foundations systems under these circumstances. Usually, the presence of superstructure is neglected and calculations are performed for free-field conditions. 

 

 

Liquefaction Impact 

The onset of liquefaction is evaluated and empirical correlations for settlements, developed for free-field conditions, are used. However, the presence of superstructure differentiates significantly the response from that under free-field conditions, so that such methods prove too approximate.