Recent Studies on Seismic Analysis and Design of Retaining Structures

The studies on seismic analysis and design of retaining walls in the recent years have revolved around the wall performance in the near-source zones. Major developments include: (1) the conventional limit equilibrium approach is extended based on the multiple failure plane concept; (2) a set of design charts for evaluating residual horizontal displacement of a gravity wall on yielding foundation are developed based on the parametric effective stress analysis; (3) applicability of the effective stress analysis on the retaining wall performance is confirmed by the case history during Hyogoken-Nambu, Kobe, earthquake; (4) major earthquake motion parameters that govern the wall displacement through soil-structure interaction analysis are spectral intensity (damping factor-20% and integration over 1.0 to 3.0 seconds) and/or frequency components lower than about 2Hz, which is lower than the fundamental natural frequency of the wall-soil system at small strain shaking. These developments in the seismic analysis of retaining walls lead us toward the performance-based design of retaining walls

Recent Earthquakes in Japan

The paper presents highlights of case histories during earthquakes in Japan in 2003. One is a river embankment of the Naruse river in Northern Miyagiken, in which the earthquake with Richter magnitude 6.2 caused failure. A particular interest in this case history is the timing of the earthquake and failure; the earthquake was coincided with the oncoming risk of flooding, with the river suffering a high water level due to continuous raining for three days before the earthquake. This warns us not to disregard the low probability event of combined risks that pose high consequence. The other case history is a gravity quay wall in Kushiro port, Hokkaido, in which the earthquake with Richter magnitude 8.0 caused minor damage. Of a particular interest in this case history is the performance of a quay wall with backfill treated with cement for solidification, which suffered settlements in the order of 0.5m. Other quay walls in the vicinity treated with densification and gravel drains suffered no damage. The investigation is under way with respect to the difference in the performance of these quay walls

Adjustment Method of the Hysteresis Damping for Multiple Shear Spring Model

In simulating the behavior of sandy soil under the cyclic loading condition using the multiple shear spring model, it is necessary to adjust the damping constant of the model. We describe a method for adjusting the constant in this paper. If you adopt the conventional Masing rule to decide the unloading curve of each spring, the entire damping constant of this model, which is superposition of those of all springs, would become larger than that measured in the laboratory for large strain level. Though the damping constant of each spring is controllable by amending the Masing rule, there is no obvious way to decide the constant of each spring. In order to reproduce the actual damping constant, we expressed the damping constant of each spring as a function of displacement at which unloading of the spring has started, and determined the coefficients of the expression from the actual damping constant. So we can amend the Masing rule for each spring so as to realize the damping constant for each spring. The method is adopted to the effective stress analysis program FLIP developed by the authors. In this paper we explain the method and show the results of the computer simulations by FLIP program

Numerical Analysis of Trampoline Effect in Extreme Ground Motion

Very large vertical surface acceleration of nearly four times gravity was measured at a strong motion observation station in Iwate Prefecture during the 2008 Iwate-Miyagi Inland, Japan, earthquake (Mw 6.9). The station is located about 3 km southwest of the epicenter and equipped with three-component accelerometers, installed at both the free surface and the bottom of a 260-m borehole. The wave form of the vertical acceleration shows a clearly asymmetric form with large amplitude in the upward direction. Aoi et al. (2008) reported and qualitatively explained the mechanism of this phenomenon by the analogy of bouncing a piece of matter on a trampoline, and thus they called it the “trampoline effect.” To simulate this recently discovered nonlinear behavior of the surface ground motion, numerical analysis with a finite-element method has been employed with parameters derived from the borehole data at the station. The analysis successfully simulates the asymmetric vertical motion. Results indicate that the asymmetric motion may be characterized by the existence of a lower bound of negative acceleration, which in most cases corresponds to the acceleration of gravity, and high positive pulses caused by the compression stress of the disturbed surface ground material

Effective Stress Analysis for Evaluating the Effect of the Sand Compaction Pile Method During the 1995 Hyogoken-Nambu Earthquake

The effect of the sand compaction pile method as a countermeasure for liquefaction mainly consists of three factors: increase in the density, increase in the horizontal effective stress and stabilization of microstructure. Proper evaluation of the effect of improvement is important for estimating the seismic behavior of the ground improved by the sand compaction pile method. How to incorporate the effect and its factors into an analytical model was investigated by simulating the seismic behavior of the ground at two sites during the 1995 Hyogoken-Nambu earthquake with the effective stress analysis method “FLIP.” It was found that not only the increase in the density but also increase in the horizontal effective stress were important in explaining the effect of the sand compaction pile method. Moreover, a model taking account of both sand piles and the improved ground between them suggested a possibility of reproducing the behavior of improved ground under large ground motions more properly

PRENOLIN project. Results of the validation phase at sendai site

One of the objectives of the PRENOLIN project is the assessment of uncertainties associated with non-linear simulation of 1D site effects. An international benchmark is underway to test several numerical codes, including various non-linear soil constitutive models, to compute the non-linear seismic site response. The preliminary verification phase (i.e. comparison between numerical codes on simple, idealistic cases) is now followed by the validation phase, which compares predictions of such numerical estimations with actual strong motion data recorded from well-known sites. The benchmark presently involves 21 teams and 21 different non-linear computations. Extensive site characterization was performed at three sites of the Japanese KiK-net and PARI networks. This paper focuses on SENDAI site. The first results indicate that a careful analysis of the data for the lab measurement is required. The linear site response is overestimated while the non-linear effects are underestimated in the first iteration. According to these observations, a first set of recommendations for defining the non-linear soil parameters from lab measurements is proposed. PRENOLIN is part of two larger projects: SINAPS@, funded by the ANR (French National Research Agency) and SIGMA, funded by a consortium of nuclear operators (EDF, CEA, AREVA, ENL)

Overview of Backwards Analysis in Geotechnical Engineering

International Symposium on Backwards Problem in Geotechnical Engineering and Monitoring of Geo-Construction, Green Hall, Kensetsu-Koryu-kan, 2011/07/14-15The authors initial thought on the backwards problem in geotechnical earthquake engineering is presented through an example of damage to caisson quaywall during earthquakes. Both a simplified and detailed dynamic analyses are presented. It is essential to confirm, at the outset, that the backwards problem.is well defined. There should be sufficient geotechnical data and earthquake data to match the analysis procedure used for solving the backwards problem. Ill-defined backwards problem, either due to lack of required geotechnical or earthquake motion data, should be corrected before the trial solution of the backwards problem

Performance-Based Design of Geotechnical Structures: Recent Advances

The paper presents an overview of recent advances in earthquake geotechnical engineering with respect to the seismic design of geotechnical structures. The modern principles in seismic design are described along the framework of performance-based design as adopted in the International Standard (ISO23469). With the growing awareness of the need to understand the effect of non-linearity in soils and soil-structure interaction, the paper discusses the highly non-linear response of ground during strong earthquake motions with a peak ground acceleration exceeding 1g, and the highly non-linear behavior of soil-pile interaction, including soil-pile separation. The modern principles in seismic design described in this paper allow a sophisticated approach to deal with the uncertainty. Discussion on this issue is provided through the life-cycle cost approach. The paper also discusses the combined hazards, such as those during the Sumatra, Indonesia, earthquake of 2004, posing a new challenge to seismic design of geotechnical structures

Numerical Predictions for Centrifuge Model Tests of a Liquefiable Sloping Ground Using a Strain Space Multiple Mechanism Model Based on the Finite Strain Theory

This paper presents the results of numerical simulations for dynamic centrifuge model tests of a liquefiable sloping ground performed by various institutions within a framework of Class A, B, and C prediction phases of the LEAP (Liquefaction Experiments and Analysis Project). The simulations are performed by using a strain space multiple mechanism model based on the finite strain theory (including both total and updated Lagrangian formulations), in which both material and geometrical nonlinearity are considered. In the simulation, dynamic response analyses are carried out following self-weight analyses with gravity. The soil parameters of the constitutive model are determined based on the results of laboratory soil tests (e.g., cyclic triaxial tests) and some empirical formulae. The identification process of the parameters is explained in details besides the computational conditions (e.g., geometric modeling, initial and boundary conditions, numerical schemes such as time integration technique). In addition to the numerical results of the Class A prediction using a target input motion, those of the Class B and C predictions using recorded motions in the centrifuge model tests are also presented. Comparison between these predictions and measured results has revealed that the constitutive model parameters for effective stress analyses should be calibrated to well capture the shape and trend of liquefaction resistance curves, and subsequently estimate the damage of soil systems due to liquefaction with higher accuracy