Back Issues 11-20

THREE CONSTITUENT ELEMENTS REQUIRED FOR CAUSING LIQUEFACTION

Tse-Shan Hsu

President, Institute of Mitigation for Earthquake Shear Banding Disasters

Professor, Feng-Chia University, Taiwan, R.O.C., This email address is being protected from spambots. You need JavaScript enabled to view it.

Yu-Chien Wu

Ph.D. Student, Ph.D. Program for Infrastructure Planning and Engineering, 

Feng-Chia University, Taiwan, R.O.C.

Zong-Lin Wu  

Assistant Professor, National Chin-Yi University of Technology, Taiwan, R.O.C

Hong-Chia Chang        Chang-Chi Tsao

Directors, Institute of Mitigation for Earthquake Shear Banding Disasters

Tsai-Fu Chuang

Associate Professors, Feng-Chia University, Taiwan, R.O.C.

Abstract

Shear bands are formed in saturated dense sand layers under lateral compression when localization of deformation is produced under unstable volume-expansion conditions of plastic strain softening after the strain goes deep into the plastic range. Liquefaction is a special failure phenomenon caused by shear banding that occurs during tectonic earthquakes. The occurrence of liquefaction encompasses three constituent elements: (1) the shear band derived from the localization of deformation, (2) the highly concentrated excess pore water pressure that is locally present in the shear band, and (3) the groundwater entrainment of small to large grained granular soils (such as silt, sand, and gravel) and their ejection upward sequentially along the outlet channel formed by pore spaces in the shear band. In comparison, the conditions for liquefaction proposed by most scholars (1) define liquefaction as occurring outside the yielding surface where stress does not in fact exist, (2) imply that the farther the stress is from the yield surface, the higher the liquefaction potential, and (3) assess the alluvial plains along the coast of Taiwan as liquefaction potential areas. Because liquefaction only occurs locally in shear bands and the proportion of the area of the shear band is small, the authors suggest that the seismic design code of buildings should incorporate the results of this study, which more accurately reflect the real conditions, so that the liquefaction disaster reduction work can be carried out more economically and effectively.

Keywords: tectonic earthquakes, liquefaction, three constituent elements, shear bands, pore water pressure, groundwater.