Pore pressure and dissipated energy in earthquakes - Field verification

The possibility of a correlation between dynamic pore pressure increase p a nd dissipated energy density D in soils subjected to earthquake shaking has been the subject of speculation for nearly 20 years. While cyclic loading tests have tended to confirm the D-p hypothesis in the laboratory, no field confirmation has been given. In this paper compelling evidence is presente d to support the D-p model from two real earthquakes. Downhole acceleration records from two earthquakes are analyzed to obtain approximate histories of shear stress, shear strain, and dissipated energy over a range of depths . The measured data were obtained from the Lotung downhole array in Taiwan and from the Sunamachi downhole array near Tokyo. Both of these arrays also contain pore pressure measurement devices, and records of pore-pressure in crease during the earthquakes are available. Time histories of measured por e pressure will be directly compared with calculated values based on the D- p hypothesis. The results of this study suggest dissipated energy density m ay be remarkably well correlated with pore pressure increase in field situa tions.