Liquefaction in the Chi-Chi earthquake - Effect of fines and capping non-liquefiable layers

The 1999 Chi-Chi, Taiwan, earthquake caused great destruction to buildings, bridges, and other facilities, and a death toll of 2470. Of particular interest to geotechnical engineers in this event is the evidence of widespread liquefaction that caused significant damage to buildings, lifelines and harbor facilities. Shortly after the earthquake, an extensive field investigation in the Yuanlin area, including in situ tests and laboratory tests, was conducted by Moh and Associates, Inc. These in situ and laboratory tests along with ground performance observations offer a chance to examine the existing methods of liquefaction potential evaluation. In this paper, 22 cases of ground performance in the Yuanlin area that experienced extensive soil liquefaction are studied. These are case histories that were well documented with field observations of ground performance in the Chi-Chi event. Attempt is made to analyze liquefaction potential using the Standard Penetration Test (SPT) data that are associated with each case history. Results of the analyses show that in general, surface manifestation of liquefaction can be fairly accurately predicted using simplified methods. In many cases where the subsurface deposit consists of alternate layers of silty clay and silty sand, however, the effect of capping clay layers must be considered in order to correctly account for the presence or lack of surface manifestation of liquefaction.