December 4, 2002 (Wednesday) - Burmister Lecture
2:30-3:30 pm, 414 CEPSR
Prof. Jean Prevost
Princeton University
Dynamic Flow Liquefaction in Geomaterials: Computational and Physical Modeling

In this talk we will discuss the liquefaction of saturated granular soil deposits under seismic excitation and resulting ground failure, loss of bearing capacity, etc.... The coupled field equations which govern the phenomenon will be derived using mixtures theories, and solved numerically using finite element techniques. Validation of the numerical model will be discussed using physical experiments such as laboratory soil tests, shaking table tests and centrifuge tests. The inherent variability of soil properties will be modeled using stochastic methods, and we will demonstrate the importance of accounting for soil spatial variability in modeling liquefaction phenomena. The numerical results will demonstate the usefullness and power of the techniques used.

Prof. Joseph Wartman
Assistant Professor of Civil, Architectural, and Environmental Engineering
Drexel University
Philadelphia, Pennsylvania

Engineering Aspects of the June 23, 2001 Southern Peru Earthquake
The June 23, 2001 magnitude (Mw) 8.4 earthquake in Southern Peru was the largest seismic event of the last 25 years. The earthquake, which was centered near Ocona, caused considerable damage to the historic cities of Arequipa, Tacna, and Moquegua.  Many highways in the region, including South America's primary north-south artery, the Pan-American Highway, also sustained significant damage. The event left over 140 people dead, 36,000 homes damaged, and 225,000 people homeless.  Professor Wartman was a member of a six-person Nation Science Foundation-sponsored U.S.-Peru team that conducted a geotechnical damage reconnaissance of the region shortly after the earthquake. His presentation will provide an overview of the event, and will focus on the performance of geotechnical structures including large dams, highway embankments, geosynthetic-lined containment facilities, foundations, and slopes.  He will also discuss some unique observations related to sites effects, a potentially devastating phenomenon whereby subsurface materials and topography amplify earthquake ground motions.  Some aspects of Peru's earthquake preparedness program and the local population’s response to the event will be noted

Mr. George E. Leventis
President, Langan International, New York City
Principal, Langan Engineering and Environmental Services

The Rion-Antirion Bridge
A Crossing of Epic Proportions over the Corinthian Straights
A million years ago the Peloponnese, Greece's southernmost peninsula, was firmly connected to the mainland, and the Gulf of Corinth did not exist. Over the course of several millennia, however, the Peloponnese began to drift southward, creating the gulf that now nearly separates much of the peninsula  (home to the city of Olympia, the site of the original Olympic Games) from the rest of Greece.

Today a slow and unreliable ferry system that transports vehicles across the gulf forms the main link between the northwestern part of Greece and the Peloponnese.  Soon an extraordinary bridge employing unique soil-enhancing and foundation techniques, the longest cable-stayed deck in the world, and innovative seismic systems will replace the ferry system and will connect the Greek mainland to the Peloponnese.

Athens-based Geyfra S. A., the BOT concession owned by six Greek contractors and France's Group VINCI, has to build the 2.9-kilometer long bridge under a lump-sum design-build contract and will operate it for 35 years. The structure includes a 2.25 km cable-stayed section with three 560 m main spans. Concrete footings, each big enough to hold almost two football fields, are now in place in the 65-m-deep Gulf of Corinth, after 15 years of hard bargaining and tough engineering.  The $650 - million Rion - Antirion project bridging the seismically active body of water will open to traffic by the end of 2004.

Mladen Vucetic
University of California at Los Angeles

KINEMATICS OF FAILURE OF SOIL-NAILED EXCAVATION MODELS IN DYNAMIC CENTRIFUGE TESTS
Soil nailing is an in-situ technique of mechanically stabilizing soil mass with passive inclusions (soil nails) as the excavation proceeds.  In spite of its popularity, relatively little is known about the behavior of soil-nailed systems during strong earthquakes.  To address this issue, a series of dynamic centrifuge tests on 14 models of soil-nailed excavations was conducted.  In these tests the length, spacing, stiffness and inclination of the nails and the stiffness of the facing were varied.  The models were cyclically deformed and eventually driven to failure under different levels of horizontal shaking.  The scaling factor was 50, with the models corresponding to 7.6 meters high prototype excavations.  The behavior of the models was recorded with series of miniature accelerometers and displacement transducers.

The lecture describes the testing procedure and elaborate data interpretation, including the kinematics and failure mechanisms of several centrifuge models tested.  The model failures are discussed in the context of seismic stability evaluation of their prototypes.

February 13, 2002
Prof. Dov Leshchinsky
University of Delaware
Numerical Investigation of The Effects of Geosynthetic Spacing on Failure Mechanisms in MSE Block Walls

ABSTRACT: This analysis used in design of mechanically stabilized earth (MSE) block walls is based on the premise that a failure surface will develop within the reinforced soil zone defining an active soil mass. Limit equilibrium analysis of this mass renders the reactive force in the reinforcement and connections. The objective of this work was to identify the effects of reinforcement spacing on failure mechanisms in block walls. A computer program, based on continuum mechanics and capable of dealing with soil at failure, was utilized. Geosynthetic connection to the blocks was purely frictional. Interfaces between stacked blocks, reinforcement and confining blocks, soil and blocks, and soil and reinforcement were modeled. In addition to spacing effects, computer simulations were conducted to study the effects of factors such as backfill strength, foundation strength, reinforcement stiffness, interface strength, and intermediate reinforcement layers. Results of the parametric studies on a surcharge-free wall show that, as the reinforcement spacing decreases, the likelihood of developing a failure or active zone entirely within the reinforced soil zone decreases. Nonexistent such failure zones, for closely spaced reinforcement, imply that current limit-equilibrium formulations and designs might be unrealistic leading to excessive reinforcement load and related length. However, based on the parameters used, it was observed that conventional failure modes, such as direct sliding and toppling, deep-seated failure, and compound instability, may occur.  Current “external stability” addresses the same identified modes and mechanisms; hence, reinforcement dimensioning based on these mechanisms seems appropriate.

Performance-based design of steel structures in fire
Arup Fire has significant expertise in the response of multi-storey steel frame buildings in fire conditions. It is possible to use a performance - based approach to calculate appropriate fire resistance times for structure and compartmentation, taking into account the actual geometry, ventilation conditions and design fire loads. This presentation will outline the basis of current code requirements for fire resistance.How code requirements relate to real structural behavior in fire will be discussed.Alternative design solutions for steel structures in fire will be outlined.Some Arup projects using such solutions will be presented. Finally ways forward will be proposed for multi-storey steel framed buildings in fire, in light of the World Trade Center collapse.

The Use of Dredged material in Concrete Applications
ABSTRACT: The dredged material disposal is environmentally problematic because of its contamination with various toxic substances, from heavy metals to oil products and pesticides. This problem is of major concern to the Greater New York Metropolitan region, because the navigational shipping lanes need to be dredged to keep the Port operable and economically viable. Scarce capacities and high costs of disposal facilities increase the demand for beneficial usage. Can concrete technology provide a solution to the dredged material problem? At Columbia, research has been conducted to beneficially use detoxified material in concrete applications. Dredged material contains organics, various salts, heavy metals and other substances, which more or less affect cement hydration and may cause chemical reactions with other concrete components. Due to its fineness, it changes also the aggregate grading in an undesirable way. Delayed setting time, poor workability and performance under load may be the consequences. It has to be assured that no contaminants leach out under normal service conditions.

Mechanical Behavior of Pisa Clay
This is an experimental investigation into the mechanical behaviour of a natural, slightly overconsolidated clay found below the Tower of Pisa. Triaxial and true triaxial stress-path controlled tests were carried out, in which the soil was subjected to a variety of drained stress paths, each starting from the in situ stresses. The observed results are interpreted using concepts of hardening plasticity and the influence of the microstructure disruption is evaluated through a normalisation procedure and by comparison with the behaviour of the reconstituted Pisa clay. The stiffness observed is seen to depend strongly on the direction of stress paths. Some indication for modelling the observed behaviour is given, and results of some model simulations are compared with experimental results.

Soil-System Identification and Inverse Problem Analyses

Strong-motion earthquake records constitute an invaluable source of information on the actual dynamic behavior of sites, earth dams, and other soil-systems. Centrifuge model tests provide meritorious complementary experimental data, especially in view of the relative scarcity of case-history seismic records. A range of system identification and inverse problem techniques were used by the speaker and co-workers to interpret and translate such experimental and observational data toward model development and calibration. A simple nonparametric identification technique was introduced to evaluate site shear stress-strain histories directly from vertical-array accelerations. This technique provides direct information on the local shear stress-strain behavior of soil strata within an instrumented zone, under condition of vertical seismic wave propagation and when the array of instruments extends to the ground surface. Lately, a novel point-wise system identification methodology and algorithm were developed to assess locally the multidimensional constitutive response of distributed soil-systems using acceleration and pore-pressure records provided by 2-D or 3-D arrays of closely spaced instruments. This algorithm does not require the availability of measurements of boundary conditions, or solution of the boundary value problem associated with an observed system.  Conversely, global identifications were used to analyze full-scale soil-systems equipped with sparse distributions of instruments installed along the boundaries. These identifications were formulated in a Bayesian setting as a combination of a priori and experimental information with theoretical knowledge to improve the problem conditioning. The field of geotechnical system identification is destined to experience significant developments over the next few years in view of the drastic and continuous improvements in sensor, instrumentation, and computer technologies, as well as the pioneering NEES (Network for Earthquake Engineering Simulation) NSF project.

A Generalized Plasticity Model for Sands and Its Application to Dynamic Analysis of Reinforced Soil Retaining Walls
The behavior of sand and performance of earth structures are strongly affected by the confining stress. Many existing models for sand are not capable of describing the behavior under ranging from very low to very high confining stresses. A generalized plasticity model is extended to capture the dilatancy and strength properties of sand under a wide range of stress levels. The model is validated with the experimental results of several different types of sand under drained and undrained conditions. The presentation includes the prediction of sand behavior under repeated loading.