Field and Experimental Evidence on the Effect of Preshaking History on the Liquefaction Resistance of Silty Sand Deposits

The paper discusses the effect of seismic preshaking history on liquefaction of silty sand soils using case histories in California, as well as experimental data. The case histories are: (a) the response of the Wildlife site in the Imperial Valley to the 2010 El-Mayor Cucapah earthquake (M_w = 7.2, a_max = 0.15g); and (b) the response of the Treasure Island Fire Station (F.S.) site in the San Francisco Bay area to the 1989 Loma Prieta earthquake (M_w = 6.9, a_max = 0.16g). Both sites are similar in almost every respect except for their seismic history. The magnitude and intensity of the corresponding earthquakes were also very similar at both locations. While Treasure Island F.S. did liquefy during the shaking, Wildlife did not and was far from liquefaction as indicated by piezometers at the site. The experiments conducted in this research were a crude simulation of the seismic history of the sites. From the results of the experimental simulation as well as the field case histories, it is concluded that preshaking by previous earthquakes is the most probable explanation of the higher liquefaction resistance exhibited by the Wildlife site and other sites in the Imperial Valley of Southern California.