Jonathan D. Bray

Bio: Jonathan D. Bray is an academic researcher from University of California, Berkeley. The author has contributed to research in topics: Liquefaction & Soil liquefaction. The author has an hindex of 52, co-authored 222 publications receiving 9256 citations. Previous affiliations of Jonathan D. Bray include University of California & Missouri University of Science and Technology.

Simplified Procedure for Estimating Earthquake-Induced Deviatoric Slope Displacements

Abstract: A simplified semiempirical predictive relationship for estimating permanent displacements due to earthquake-induced deviatoric deformations is presented. It utilizes a nonlinear fully coupled stick-slip sliding block model to capture the dynamic performance of an earth dam, natural slope, compacted earth fill, or municipal solid-waste landfill. The primary source of uncertainty in assessing the likely performance of an earth/waste system during an earthquake is the input ground motion. Hence, a comprehensive database containing 688 recorded ground motions is used to compute seismic displacements. A seismic displacement model is developed that captures the primary influence of the system’s yield coefficient ( ky ) , its initial fundamental period ( Ts ) , and the ground motion’s spectral acceleration at a degraded period equal to 1.5 Ts . The model separates the probability of “zero” displacement (i.e., ⩽1 cm ) occurring from the distribution of “nonzero” displacement, so that very low values of calculated...

Simplified Frequency Content Estimates of Earthquake Ground Motions

Abstract: It is often useful in earthquake engineering practice to characterize the frequency content of an earthquake ground motion with a single parameter. Three simplified frequency content parameters are examined: mean period (T m ), predominant period (T p ), and the smoothed spectral predominant period (T o ). These frequency content parameters are calculated for 306 strong motion recordings from 20 earthquakes in active plate-margin regions. These data are used to develop a model that describes the magnitude, distance, and site dependence of these frequency content parameters. Nonlinear regression analyses are performed to evaluate model coefficients and standard error terms. The results indicate that the traditional T p parameter has the largest uncertainty in its prediction, and that previous relationships proposed to predict T p are inconsistent with the current data set. Moreover, T m is judged to be the best simplified frequency content characterization parameter, and it can be reliably estimated.

Assessment of the Liquefaction Susceptibility of Fine-Grained Soils

Abstract: Observations from recent earthquakes and the results of cyclic tests indicate that the Chinese criteria are not reliable for determining the liquefaction susceptibility of fine-grained soils. Fine-grained soils that liquefied during the 1994 Northridge, 1999 Kocaeli, and 1999 Chi-Chi earthquakes often did not meet the clay-size criterion of the Chinese criteria. Cyclic testing of a wide range of soils found to liquefy in Adapazari during the Kocaeli earthquake confirmed that these fine-grained soils were susceptible to liquefaction. It is not the amount of “clay-size” particles in the soil; rather, it is the amount and type of clay minerals in the soil that best indicate liquefaction susceptibility. Thus plasticity index (PI) is a better indicator of liquefaction susceptibility. Loose soils with PI 0.85 were susceptible to liquefaction, and loose soils with 12 0.8 were systematically more resistant to liquefaction. Soils with PI>18 tested at low effective confining stresses ...

Recent Advances in Soil Liquefaction Engineering: A Unified and Consistent Framework

Abstract: Over the past decade, major advances have occurred in both understanding and practice with regard to assessment and mitigation of hazard associated with seismically induced soil liquefaction. Soil liquefaction engineering has evolved into a sub-field in its own right, and engineering assessment and mitigation of seismic soil liquefaction hazard is increasingly well addressed in both research and practice. This rapid evolution in the treatment of liquefaction has been pushed largely by a confluence of lessons and data provided by a series of major earthquakes over the past dozen years, as well as by the research and professional/political will engendered by these major seismic events. The overall field of soil liquefaction engineering is now beginning to coalesce into an internally consistent and comprehensive framework, and one in which the various elements are increasingly mutually supportive of each other. Although the rate of progress has been laudable, further advances are occurring, and more remains to be done. As we enter a “new millenium”, engineers are increasingly well able to deal with important aspects of soil liquefaction engineering. This paper will highlight a number of important recent and ongoing developments in soil liquefaction engineering, and will offer insights regarding research in progress, as well as suggestions regarding further advances needed. 1 Dept. of Civil and Environmental Engineering, University of California, Berkeley. 2 Dept. of Civil Engineering, Middle East Technical University, Ankara, Turkey. 3 Fugro Engineering, Santa Barbara, California. 4 Arup, San Francisco, California. 5 URS Corporation, Oakland, California. 6 U.S. Geological Survey, Menlo Park, California. 1.0 INTRODUCTION Soil liquefaction is a major cause of damage during earthquakes. “Modern” engineering treatment of liquefactionrelated issues evolved initially in the wake of the two devastating earthquakes of 1964; the 1964 Niigata (Japan) and 1964 Great Alaskan Earthquakes. Seismically-induced soil liquefaction produced spectacular and devastating effects in both of these events, thrusting the issue forcefully to the attention of engineers and researchers. Over the nearly four decades that have followed, significant progress has occurred. Initially, this progress was largely confined to improved ability to assess the likelihood of initiation (or “triggering”) of liquefaction in clean, sandy soils. As the years passed, and earthquakes continued to provide lessons and data, researchers and practitioners became increasingly aware of the additional potential problems associated with both silty and gravelly soils, and the important additional issues of post-liquefaction strength and stressdeformation behavior also began to attract increased attention. Today, the area of “soil liquefaction engineering” is emerging as a semi-mature field of practice in its own right. This area now involves a number of discernable sub-issues or subtopics, as illustrated schematically in Figure 1. As shown in Figure 1, the first step in most engineering treatments of soil liquefaction continues to be (1) assessment of “liquefaction potential”, or the risk of “triggering” (initiation) of liquefaction. There have been major advances here in recent years, and some of these will be discussed. Once it is determined that occurrence of liquefaction is a potentially serious risk/hazard, the process next proceeds to assessment of the consequences of the potential liquefaction. This, now, increasingly involves (2) assessment of available post-liquefaction strength, and resulting post-liquefaction overall stability (of a site, and/or of a structure or other built facilities, etc.). There has been considerable progress in

Simulation of Ground Motion Using the Stochastic Method

Abstract: A simple and powerful method for simulating ground motions is to combine parametric or functional descriptions of the ground motion’s amplitude spectrum with a random phase spectrum modified such that the motion is distributed over a duration related to the earthquake magnitude and to the distance from the source. This method of simulating ground motions often goes by the name “the stochastic method.” It is particularly useful for simulating the higher-frequency ground motions of most interest to engineers (generally, f > 0.1 Hz), and it is widely used to predict ground motions for regions of the world in which recordings of motion from potentially damaging earthquakes are not available. This simple method has been successful in matching a variety of ground-motion measures for earthquakes with seismic moments spanning more than 12 orders of magnitude and in diverse tectonic environments. One of the essential characteristics of the method is that it distills what is known about the various factors affecting ground motions (source, path, and site) into simple functional forms. This provides a means by which the results of the rigorous studies reported in other papers in this volume can be incorporated into practical predictions of ground motion.