Liquefaction-Induced Ground Damage in Dagupan in the July 16, 1990 Luzon Earthquake

Abstract

ABSTRACT Geotechnical aspects of the ground damage caused by widespread occurrence of liquefaction at the time of the 1990 Luzon, Philippines earthquake are highlighted by examining the geomorphological regime and boring data obtained in the city area of Dagupan. The comparison of old and present locations of the river courses indicates that the liquefaction in the city of Dagupan had taken place in two geomorphologically different areas: namely, the terrain of naturally buried old river channels and the area of point bar deposits. Although impossible to distinguish soil profile characteristics between these two types of terrains, the common feature is that there exists a surface layer composed of unliquefiable silty soils, underlain by sand deposits which are loose enough to provoke liquefaction. As a result of simple analysis of liquefaction, it was shown that the upper part of this sand deposits developed liquefaction, leading to the disastrous consequences in the city of Dagupan. By compiling a number of SPT data and the data of Swedish cone penetration tests, an attempt was made to clarify the relationship between the thickness of unliquefiable surface layer and that of the underlying liquefied layer which can or can not bring about surface manifestation of liquefaction, accompanied by disastrous damage on the ground surface. Lastly, the lateral spreads of the ground near the riverside were analyzed by considering the soil profiles established by the Swedish cone tests. The residual strength determined by back-calculation at three typical cross sections indicated a general coincidence with those estimated previously for other data sets.