Estimation of Liquefaction-Induced Ground Settlement (Case Studies)

Over the past decade, the focus of liquefaction engineering began to shift towards assessment of the consequences of liquefaction with respect to the seismic performance of engineered structures and facilities, which requires accurate and reliable tools for prediction of ground deformations over the small to moderate range. Promising new predictive tools are evolving. These include simplified, empirical tools as well as sophisticated analytical and constitutive models. Recently, a high quality laboratory testing program consisting of undrained, cyclic simple shear testing on fully-saturated samples of Monterey No. 0/30 sand was completed at U.C. Berkeley. As a result, a new semiempirical procedure was proposed for predicting post-liquefaction volumetric reconsolidation ground settlements in essentially level ground (α ≈ 0 conditions). This new procedure also includes modification for predicting liquefaction-induced ground settlement in sloping or near free-face ground (α ≠ 0 conditions). The new procedure was shown to perform well for a suite of field performance case histories with small-to-moderate ground settlements, comparing with existing semi-empirical engineering tools for estimating liquefaction-induced ground deformations

Compaction-Induced Distress of a Long-Span Culvert Overpass Structure

Compaction of backfill produces soil stresses and earth pressures which are not amenable to analysis by conventional methods. These compaction-induced earth pressures can produce stresses and deformations in flexible buried culvert structures which may significantly affect the stability and performance of these structures. This paper presents the results of a study in which deformations of a long-span flexible metal culvert were measured during carefully monitored backfill operations. These field measurements were then compared with the results of finite element analyses in order to investigate (a) the influence of compaction effects on culvert stresses and deformations, and (b) the ability of recently developed finite element analysis procedures to accurately model these compaction effects. The structure being monitored suffered excessive and unacceptable deformations which were shown to be primarily the result of compaction effects; these were well modelled by the analyses performed

Shaking Table Experiment of a Model Slope Subjected to a Pair of Repeated Ground Motions

This paper describes the third of a series of six shaking table experiments conducted as part of ongoing research to evaluate the accuracy and applicability of the Newmark (1965) procedure for computing seismically induced deformation in slopes. A cohesive model slope was shaken by two identical test motions in succession, mimicking a situation that commonly occurs when a preexisting landslide is subjected to strong earthquake shaking. Back analyses of the tests showed that the Newmark (1965) formulation provided moderately accurate estimates of the measured permanent deformations (within 40% to 85% of the maximum measured displacement). The accuracy of the Newmark (1965) formulation was greatest when displacement-dependent degrading yield acceleration was used to model the soil’s transition from peak to residual shear strength. The Newmark analyses were most reliable for the second test that experienced relatively large deformations, and thus where the sliding resistance was controlled by post-peak to residual strength

The Kettleman Hills Landfill Failure: A Retrospective View of the Failure Investigations and Lessons Learned

The sliding stability failure of the Kettleman Hills waste landfill focused attention on several issues related to the safe design and filling of waste repositories, including low strengths between geosynthetic material interfaces in composite liner systems and low interface strength between compacted clay and smooth geomembranes. Waste placement plans must be carefully developed to insure an adequate factor of safety against sliding at all stages of filling. Because of assumptions and uncertainties that remained following the initial failure investigation, model tests, at a scale of 1:150, were done. These tests reproduced the field failure very well and provided insights into the failure mechanisms. A three-dimensional method for stability analysis gave results in close agreement with field observations and the results of a subsequent detailed failure investigation done by others (Byrne et al., 1992). Those special cases of landfill geometry and liner properties for which the 3D stability may be more critical than that computed using usual 2D methods of analysis could then be determined

Ground Motions from the Northridge Earthquake

The magnitude, duration and frequency content of ground motions from the Northridge Earthquake are analyzed and compared to predictive relationships typically used in engineering design and to the 1994 Uniform Building Code. The effect of geologic conditions on localized damage patterns is shown to be important for this earthquake, even though many of the sites within the affected region are stiff soil sites classified as UBC sites S1 or S2

Liquefaction of Soils in the 1989 Loma Prieta Earthquake

The Loma Prieta Earthquake of October 17, 1989 was the most costly single natural disaster in U.S. history, resulting in losses of $7 to$9 billion, and claiming 63 lives. These damages were concentrated mainly at a number of distinct sites comprising a relatively small fraction of the affected region, as local site conditions and related geotechnical factors exerted a major influence on damage patterns and loss of life in this catastrophic event. This paper discusses one of these geotechnical factors, the widespread occurrence of soil liquefaction during the earthquake, as well as the associated damages and the resulting lessons learned. Additional significant geotechnical factors which exerted a strong influence on damage patterns during this event, including site-dependent dynamic response and seismically-induced slope instability, are discussed in companion papers in these proceedings

Standard Penetration Test-Based Probabilistic and Deterministic Assessment of Seismic Soil Liquefaction Potential

This paper presents new correlations for assessment of the likelihood of initiation (or “triggering”) of soil liquefaction. These new correlations eliminate several sources of bias intrinsic to previous, similar correlations, and provide greatly reduced overall uncertainty and variance. Key elements in the development of these new correlations are (1) accumulation of a significantly expanded database of field performance case histories; (2) use of improved knowledge and understanding of factors affecting interpretation of standard penetration test data; (3) incorporation of improved understanding of factors affecting site-specific earthquake ground motions (including directivity effects, site-specific response, etc.); (4) use of improved methods for assessment of in situ cyclic shear stress ratio; (5) screening of field data case histories on a quality/uncertainty basis; and (6) use of high-order probabilistic tools (Bayesian updating). The resulting relationships not only provide greatly reduced uncertainty, they also help to resolve a number of corollary issues that have long been difficult and controversial including: (1) magnitude-correlated duration weighting factors, (2) adjustments for fines content, and (3) corrections for overburden stress

Investigation of the Performance of the New Orleans Flood Protection System in Hurricane Katrina on August 29, 2005: Volume 1

This report presents the results of an investigation of the performance of the New Orleans regional flood protection system during and after Hurricane Katrina, which struck the New Orleans region on August 29, 2005. This event resulted in the single most costly catastrophic failure of an engineered system in history. Current damage estimates at the time of this writing are on the order of $100 to$200 billion in the greater New Orleans area, and the official death count in New Orleans and southern Louisiana at the time of this writing stands at 1,293, with an additional 306 deaths in nearby southern Mississippi. An additional approximately 300 people are currently still listed as “missing”; it is expected that some of these missing were temporarily lost in the shuffle of the regional evacuation, but some of these are expected to have been carried out into the swamps and the Gulf of Mexico by the storm’s floodwaters, and some are expected to be recovered in the ongoing sifting through the debris of wrecked homes and businesses, so the current overall regional death count of 1,599 is expected to continue to rise a bit further. More than 450,000 people were initially displaced by this catastrophe, and at the time of this writing more than 200,000 residents of the greater New Orleans metropolitan area continue to be displaced from their homes by the floodwater damages from this storm event. This investigation has targeted three main questions as follow: (1) What happened?, (2) Why?, and (3) What types of changes are necessary to prevent recurrence of a disaster of this scale again in the future? To address these questions, this investigation has involved: (1) an initial field reconnaissance, forensic study and data gathering effort performed quickly after the arrival of Hurricanes Katrina (August 29, 2005) and Rita (September 24, 2005), (2) a review of the history of the regional flood protection system and its development, (3) a review of the challenging regional geology, (4) detailed studies of the events during Hurricanes Katrina and Rita, as well as the causes and mechanisms of the principal failures, (4) studies of the organizational and institutional issues affecting the performance of the flood protection system, (5) observations regarding the emergency repair and ongoing interim levee reconstruction efforts, and (6) development of findings and preliminary recommendations regarding changes that appear warranted in order to prevent recurrence of this type of catastrophe in the future. In the end, it is concluded that many things went wrong with the New Orleans flood protection system during Hurricane Katrina, and that the resulting catastrophe had it roots in three main causes: (1) a major natural disaster (the Hurricane itself), (2) the poor performance of the flood protection system, due to localized engineering failures, questionable judgments, errors, etc. involved in the detailed design, construction, operation and maintenance of the system, and (3) more global “organizational” and institutional problems associated with the governmental and local organizations responsible for the design, construction, operation, maintenance and funding of the overall flood protection system