Effects Of Soil Nonlinearity Research Articles

Nonlinear soil response in the vicinity of the Van Normal Complex following the 1994 Northridge, California, earthquake

AbstractGround-motion recording obtaineds at the Van Norman Complex from the 1994 Northridge, California, mainshock and its aftershocks constitute an excellent data set for the analysis of soil response as a function of ground-motion amplitude. We searched for nonlinear response by comparing the Fourier spectral ratios of two pairs of sites for ground motions of different levels, using data from permanent strong-motion recorders and from specially deployed portable instruments. We also compared the amplitude dependence of the observed ratios with the amplitude dependence of the theoretical ratios obtained from 1-D linear and 1-D equivalent-linear transfer functions, using recently published borehole velocity profiles at the sites to provide the low-strain material properties. One pair of sites was at the Jensen Filtration Plant (JFP); the other pair was the Rinaldi Receiving Station (RIN) and the Los Angeles Dam (LAD). Most of the analysis was concentrated on the motions at the Jensen sites. Portable seismometers were installed at the JFP to see if the motions inside the structures housing the strong-motion recorders differed from nearby free-field motions. We recorded seven small earthquakes and found that the high-frequency, low-amplitude motions in the administration building were about 0.3 of those outside the building. This means that the lack of high frequencies on the strong-motion recordings in the administration building relative to the generator building is not due solely to nonlinear soil effects. After taking into account the effects of the buildings, however, analysis of the suite of strong- and weak-motion recordings indicates that nonlinearity occurred at the JFP. As predicted by equivalent-linear analysis, the largest events (the mainshock and the 20 March 1994 aftershock) show a significant deamplification of the high-frequency motion relative to the weak motions from aftershocks occurring many months after the mainshock. The weak-motion aftershocks recorded within 12 hours of the mainshock, however, show a relative deamplification similar to that in the mainshock. The soil behavior may be a consequence of a pore pressure buildup during large-amplitude motion that was not dissipated until sometime later. The motions at (RIN) and (LAD) are from free-field sites. The comparison among spectral ratios of the mainshock, weak-motion coda waves of the mainshock, and an aftershock within ten minutes of the mainshock indicate that some nonlinearity occurred, presumably at (RIN) because it is the softer site. The spectral ratio for the mainshock is between that calculated for pure linear response and that calculated from the equivalent-linear method, using commonly used modulus reduction and damping ratio curves. In contrast to the Jensen sites, the ratio of motions soon after the high-amplitude portion of the mainshock differs from the ratio of the mainshock motions, indicating the mechanical properties of the soil returned to the low-strain values as the high-amplitude motion ended. This may indicate a type of nonlinear soil response different from that affecting motion at the Jensen administration building.

Non-Linear Soil Properties and Impedances for Axially Vibrating Pile Elements

ABSTRACT Dynamic soil properties around axially vibrating piles are generally non-uniform even in homogeneous soils. This is a result of the non-linear soil reaction to the radially decreasing stresses and strains induced by the pile, as well as the slippage at the pile-soil interface. To improve the accuracy of analytical computations, this paper focusses upon the nonlinear soil response anticipated in the field and establishes the radial variation of soil properties based on commonly reported experimental data. In addition, solutions are presented for the corresponding impedance of the springs and dashpots used to represent soil in a Winkler-type analysis of axially vibrating piles. Slippage at the pile soil interface is taken into account assuming a rigid-perfectly plastic contact between the pile and the soil. To assess the relative effects of soil nonlinearity in practical applications, analytical results for different pile, load and soil conditions are presented in the form of diagrams and simple approximate relationships.

Strong Motion Seismology in Japan.

This paper reviews strong motion seismology in Japan. It describes advances in strong motion seismology in the last decade, the current state of the art, and unresolved issues in the following areas: (1) Observation and data processing of strong ground motion, (2) Local site effects, and (3) Simulation and prediction of strong ground motion. In the first area, it reviews the current state of strong motion observation and data processing: fundamental subjects in strong motion seismology. In the next area, it describes empirical evaluations of site amplification factors, effects of soil nonlinearity, effects of topographical and subsurface irregularity, and application of microtremors. In the last area, it summarizes the results of empirical, semi-empirical, and numerical techniques for the simulation and the prediction of strong ground motions due to actual earthquakes. Finally, future directions of research are suggested, based on the current state of the art in strong motion seismology.

Nonlinear Lateral, Rocking, and Torsional Vibration of Rigid Foundations

Two‐ and three‐dimensional finite element (FE) analyses are performed to investigate the influence of nonlinear soil behavior on the dynamic response of harmonically excited rigid foundations. Lateral, rocking, and torsional vibration modes are considered. An elastoviscoplastic constitutive model with kinematic hardening is assumed for the foundation soil, and computations are done implicitly in the time domain. The foundation responses for lateral, rocking, and torsional modes are characterized by increased vibrational amplitudes due to material stiffness degradation. Furthermore, resonance frequencies are created that resemble those observed for vertically oscillating finite‐size foundations. Nonlinear soil effects are shown to be dominant over a wide range of excitation frequencies for foundations vibrating in torsional and lateral modes. In contrast, nonlinear soil effects are shown to be dominant over a much narrower range of excitation frequencies for the rocking mode. The methodology presented in this paper is useful for nonlinear vibration and transient soil‐structure interaction (SSI) analysis.

Effect of soil nonlinearity on interactive behaviour of unsymmetrically loaded plane frames : Viladkar, M N; Godbole, P N; Noorzaei, J Proc Ninth Danube European Conference on Soil Mechanics and Foundation Engineering, Budapest, 2–5 October 1990P155–163. Publ Budapest: Akademiai Kiado, 1990

Effect of soil nonlinearity on interactive behaviour of unsymmetrically loaded plane frames : Viladkar, M N; Godbole, P N; Noorzaei, J Proc Ninth Danube European Conference on Soil Mechanics and Foundation Engineering, Budapest, 2–5 October 1990P155–163. Publ Budapest: Akademiai Kiado, 1990

Field evaluation and site response identification at SMART-1 site

The purpose of this paper is to study the dynamic characteristics of soil deposits during earthquake excitation. Generally, soil deposits are known to exhibit significant nonlinear behavior under strong earthquake excitations. Observation of soil earthquake response from ground surface and downhole data provides the information on the differences between strong motion and weak motion, and the effect of soil nonlinearity during strong earthquakes is also examined. Based on the evolutionary power spectral analysis, simplified wave type separation can be done. The soil amplification due to body waves is quite significant in the present study of three earthquake events. A systematic identification method is proposed to identify the hysteresis behavior of soil deposits. The extended Kalman filtering technique is applied to identify the bilinear model parameters of soil restoring forces during strong shaking.