Nonlinear Behavior of Surface Deposit During the 1995 Hyogoken-Nambu Earthquake

Abstract

Behavior of the ground during the 1995 Hyogoken-Nambu earthquake is investigated through various analyses on and comparisons with the earthquake records. Behavior of the Holocene clay, a soft clay layer, as well as the fill, the liquefied layer, is shown to affect the response of the ground significantly through effective stress analysis. Earthquake response analysis carried out on the section passing the Sannomiya station indicates that the existence of the Holocene clay and its thickness controls the response of the ground surface to a great degree. It is also shown that there was no deamplification effect caused by the nonlinear behavior of the soil in the area called the damage belt, where damage to houses was especially severe. Incident waves on the top of the upper Osaka Group formation are estimated for several sites where earthquake records were obtained by deconvolution analysis. Their waveforms on the base layer are very similar to each other in a narrow region a few kilometers wide, but are different from those at distant sites, although their PGV are nearly the same at about 80 cm/s. It is shown that the ground shaking observed at the 1995 Hyogoken-Nambu earthquake was characterized mainly by the surface geology, and that it was are controlled by the nonlinear behavior of the soft clay layer and liquefaction of fill.

Evaluation Methods of Vertical Subgrade Reaction Modulus and Rotational Resistance Moment for Seismic Design of Embedded Foundations

“…From the results, the calculation equation ( 10) of the SRM was obtained. The SRM calculation equation in the JSHB is shown in (11). The SRM calculation equation in this study has a weaker FW dependency than that in the JSHB, correlating with [7].…”

“…where G ma is the reference shear rigidity (kN/m 2 ) and N 131 is the equivalent N-value for the reference effective overburden pressure of 131kN/m 2 . The ground shear rigidity G m at each depth is calculated using [11]:…”

Earthquake Response of an Open-Type Wharf With a Pneumatic Caisson Foundation

“…With the increase of depth, the mean effective confining pressure will increase and the elastic shear modulus will rise as well. The confining pressure dependency is considered to be proportional to the 0.5th power of the mean effective confining pressure [13] as shown in eqn (4)…”

Dilatancy-Induced P Waves as Evidence for Nonlinear Soil Behavior

“…It is not because the nonlinearity reduces the wave velocity that amplification takes place, but because the grain pressure decreases with decreasing depth, which controls shear and bulk moduli and in consequence shear-wave velocity. Amplification, deamplification, and wave-propagation velocities depend on the local geologic conditions (i.e., whether seismic-wave paths lead through soft or stiff, loose or dense soilsor through cohesive or noncohesive formations) and on the frequency content and displacement amplitude of the propagating wave that determines the hysteretic behavior (Jarpe et al, 1988;Chin and Aki, 1991;Darragh and Shakal, 1991;Aki, 1993;Beresnev and Wen, 1996;Sato et al, 1996;Studer and Koller, 1997;Suetomi and Yoshida, 1998;Dimitriu et al, 1999;Dimitriu et al, 2000) and have been numerically modeled (Yu et al, 1992). One important aspect has been whether soil behavior during a strong earthquake can be derived from weak-motion data, an endeavor that has been shown not to be advisable (Bolt, 1995).…”

“…An extreme case of nonlinear soil behavior is highly significant to foundation engineers and can be attributed to the category of deamplification with regard to shear-wave propagation: the property of nearly and fully saturated sands to liquefy during undrained shear produces an excess pore water pressure increase and subsequently a drastic reduction of grain pressure (Terzaghi and Peck, 1967;Castro, 1969), which significantly reduces the shear modulus (Drnevich, 1972;Sato et al, 1996;Pease and O'Rourke, 1997;Suetomi and Yoshida, 1998) and hence shear-wave amplitude (Loukachev et al, 2000;Yang et al, 2000;Gudehus et al, 2001). Very loose soils can even completely liquefy, that is, the soil turns into a suspension allowing large deformations, hence inhibiting any shear-wave propagation (Loukachev, 2002).…”