Liquefaction potential assessment of Western Manila

• Main Author: Dungca, Jonathan R.
• Format: text
• Published: Animo Repository 2005
• Subjects: Soil liquefaction—Philippines—Manila; Shear waves; Civil and Environmental Engineering; Civil Engineering
• Online Access: https://animorepository.dlsu.edu.ph/faculty_research/6482
• Institution: De La Salle University

The geotectonic setting of the Philippines makes it prone to various types of seismic related hazards. The devastating Luzon earthquake of 1990 is one of the most recent manifestations of this phenomenon and it has also opened opportunities to better understand the liquefaction phenomenon. Dagupan City suffered tremendous loses in terms of lives and properties not only because of the violent shaking of the structures but mainly because of the liquefaction of the foundation soils. Thick liquefiable sand layer predominantly underlies Dagupan City. Many areas in the Philippine archipelago including parts of Metro Manila is believed to have similar geologic settings as Dagupan City where deposits of potentially liquefiable sand exist and are presently used for residential, commercial or industrial purposes. It is in this premise that this study was initiated to be able to make effective liquefaction potential assessments of selected areas vulnerable to liquefaction. Manila’s physiographic and geologic settings render it prone to various types of natural hazards such as earthquakes. Consistently increasing population and human activities associated with urbanization unmatched by the development of urban services and disaster mitigation have given rise to a number of environmental problems and increased vulnerability to disasters. The general subsurface condition of Manila consists primarily of upper, loose to medium, silty sand; followed by the soft to medium clayey silt of silty clay; stiff to very stiff clay; and finally the hard clay and the underlying granular deposits and/or bedrock. This upper sand layer, which has an average thickness of 9 meters in the western Manila, is believed to be prone to earthquake-induced liquefaction. Assessment of liquefaction potential of the western Manila was conducted by collecting SPT borehole data and evaluating the SPT “N” values using the semi-empirical procedures of Idriss and Boulanger (2004) for evaluating liquefaction potential during earthquakes. Another assessment procedure, using the shear wave velocity data from the series of microtremor testing conducted by Dy (2000) in the same area was used. The factors for safety against liquefaction that was computed from the two assessment procedures were analyzed.