Geologic Conditions Underlying the 2005 17th Street Canal Levee Failure in New Orleans

A careful program of subsurface sampling and cone penetration test soundings was employed to characterize the geologic conditions beneath the failed portion of the 17th Street Canal levee in New Orleans, where a 150?m long section of the levee and floodwall translated up to ～ 16?m when flood waters rose to 1–2?m of the wall’s crest on August 29, 2005, during Hurricane Katrina. The subsurface conditions are characterized by discrete layers of fill placed upon the historic cypress swamp, which is underlain by a deeper, prehistoric cypress swamp. These swamp deposits were consolidated beneath the levee, and in the area of the 2005 failure, the swamp materials infilled a natural depression believed to be an old slough, which dipped below the sheetpile tips for a distance of about 50?m, which corresponds to where the breach appears to have initiated. Detailed examination of the recovered soils suggest that recent hurricanes periodically inundated the swamps with saline and/or brackish water, which cause a mass dieoff of swamp vegetation and flocculation of suspended clays, due to the sudden increase in salinity. These conditions promote deposition of discontinuous clay seams beneath layers of organics, which are then covered by fresh water swamp deposits. This sequence is repeated, like a series of tree rings, throughout the swamp deposits. The cypress swamp deposits lying beneath the levee also exhibit high hydraulic conductivity. These materials contain corky wood, and recovered samples often exhibited densities less than water. Nine of the post-Katrina borings recovered intact samples of a basal rupture surface comprised of organic silty clay exhibited near zero residual shear strength after shearing 80 to 100 mm.     

Motions of alloying additions during furnace tapping in steelmaking processing operations

Numerical computations were carried out to describe the subsurface trajectories of spherically shaped particles (alloy additions) during simulated furnace to ladle tapping operations in steel-making. Complementing this, experiments in a 0.15 scale water model ladle of a 250 ton teeming ladle were also carried out so as to simulate the subsurface trajectories and total immersion times of various alloy additions as a function of (steel) jet orientation, jet entry locations, particle (alloy additions) entry location, particle shape, density,etc. Similarity criteria for model and prototype were deduced on the basis of Froude modeling. The possibilities of additions of various density being entrained into the bulk liquid and under-going prolonged subsurface motion were examined for a variety of operating conditions. It was found, however, that buoyant spherical particles with apparent densities ranging between 0.4 and 0.9 would, when projected into a recirculating water bath at velocities of 2.7 m/s, record total immersion times of only 0.1 to 40 seconds. The implications of the water model study, together with some idealized sets of computations for an industrial size 250 ton ladle, are analyzed from the viewpoint of industrial alloy addition practices. Finally, the results are examined with reference to different shaped particles and multi-particle addition procedures, since the latter are more typical of industrial practice. Formerly Doctoral Candidate, Department of Mining and Metallurgical Engineering, McGill University Formerly Assistant Professor, Department of Metallurgical Engineering, Indian Institute of Technology, Kanpur, 208016, India     

Stability of I-Walls in New Orleans during Hurricane Katrina

Failures of I-walls during Hurricane Katrina were responsible for many breaches in the flood protection system in New Orleans. Six breaches were examined in detail by Task Group 7 of the Interagency Performance Evaluation Taskforce. Four of these failures and breaches, which occurred before the water levels reached the top of the wall, were not caused by overtopping erosion. The failure of the I-wall at the 17th Street Canal resulted from shear through the weak foundation clay. The south failure of the London Avenue I-wall was caused by subsurface erosion, which carried massive amounts of sand inland, and removed support for the wall, leading to catastrophic instability. At the north breach on London Avenue, the failure was caused by high pore pressures, combined with a lower friction angle in the loose sand, which resulted in gross instability of the I-wall under the water pressure load from the storm surge. Looking back, with the benefit of 20-20 hindsight, these stability and erosion failures can be explained in terms of modern soil mechanics, exploration techniques, laboratory test procedures, and analysis methods. An important factor in all of the cases investigated was development of a gap behind the wall as the water rose against the wall and caused it to deflect. Formation of the gap increased the load on the wall, because the water pressures in the gap were higher than the earth pressures that had acted on the wall before the gap formed. Where the foundation soil was clay, formation of a gap eliminated the shearing resistance of the soil on the flood side of the wall, because the slip surface stopped at the gap. Where the foundation soil was sand, formation of the gap opened a direct hydraulic connection between the water in the canal and the sand beneath the levee. This hydraulic short circuit made seepage conditions worse, and erosion due to underseepage more likely. It also increased the uplift pressures on the base of the levee and marsh layer landward of the levee, reducing stability. Because gap formation has such important effects on I-wall stability, and because gaps behind I-walls were found in many locations after the storm surge receded, the presence of the gap should always be assumed in I-wall design studies.     

Nonlinear Dynamic Properties of a Fibrous Organic Soil

The nonlinear dynamic properties of a fibrous peaty organic soil beneath a levee in the Sacramento–San Joaquin Delta in California are described herein. Thin-walled tube samples were obtained from four locations between the levee crest and the free field such that the in situ vertical effective stresses (σvo′) ranged from about 12 kPa in the free field to about 135 kPa beneath the levee crest. The peaty organic soil was very soft and highly compressible in the free field with initial water contents (wo) of 236–588% and shear wave velocities (Vs) of typically 22–27 m/s, and moderately firm beneath the levee crest with wo of 152–240% and Vs of typically 88–129 m/s. Stress–strain measurements in a cyclic triaxial device showed that the normalized secant shear modulus (G/Gmax) and equivalent damping ratio (ξ) versus cyclic shear strain amplitude (γc) relations were dependent on the consolidation stress (σvc′). Tests involving prior overstraining followed by reconsolidation showed that the effects of sample disturbance were likely small. Stress history, creep, and loading frequency effects were also examined. Tests on reconstituted specimens provided supplementary data on the functional relation between maximum shear modulus (Gmax) and consolidation stress conditions. Summary relations are provided for G/Gmax and ξ versus γc and for Gmax versus σvc′.     

Influence of Boundary Conditions in a Finite-Element Analysis of River Levees

The effects of boundary conditions on the stability of a river levee built on a low-permeability soil layer overlying a coarse-grained deposit were studied by using the finite-element method (FEM). The FEM analyses could predict stable or unstable levee conditions depending on the assumed distance between the levee and the external boundary of the mesh where the water table was assumed undisturbed. Possible causes of this notable drawback are discussed. The calibration of the numerical seepage model, through a back analysis of piezometer measurements, that could limit the observed boundary effects is suggested.     

Liquefaction and Soil Failure During 1994 Northridge Earthquake

The 1994 Northridge, Calif., earthquake caused widespread permanent ground deformation on the gently sloping alluvial fan surface of the San Fernando Valley. The ground cracks and distributed deformation damaged both pipelines and surface structures. To evaluate the mechanism of soil failure, detailed subsurface investigations were conducted at four sites. Three sites are underlain by saturated sandy silts with low standard penetration test and cone penetration test values. These soils are similar to those that liquefied during the 1971 San Fernando earthquake, and are shown by widely used empirical relationships to be susceptible to liquefaction. The remaining site is underlain by saturated clay whose undrained shear strength is approximately half the value of the earthquake-induced shear stress at this location. This study demonstrates that the heterogeneous nature of alluvial fan sediments in combination with variations in the ground-water table can be responsible for complex patterns of permanent ground deformation. It may also help to explain some of the spatial variability of strong ground motion observed during the 1994 earthquake.     

Investigation of Seismic Behavior and Infill Wall Effects for Prefabricated Industrial Buildings in Turkey

Recently, Turkey has been hit by several moderate to large earthquakes that resulted in significant loss of life and property. The 1998 Adana and 1999 Marmara earthquakes caused severe damage not only in residential buildings but also in industrial buildings. Most of the industrial buildings in Turkey are constructed as prefabricated structures. Prefabricated structures are preferred because of their economic and rapid production. In the present study, the earthquake behavior and infill wall effects for single story hinged industrial prefabricated buildings were investigated. Nonlinear pushover, performance-based, time history, and fragility analyses were carried out for a sample prefabricated industrial building. Infill wall effect was investigated by adopting a diagonal strut model. The structural behavior and load-deformation relationship of prefabricated industrial buildings both with and without infilled walls were evaluated and compared. Results of the study show that masonry infill walls can affect the lateral load-carrying capacity and modify the earthquake response of prefabricated industrial buildings.     

Conceptual Model for the Safe Withdrawal of Freshwater from Coastal Aquifers

The effect of subsurface barrier on the motion of the saltwater—freshwater interface in coastal aquifers is analyzed for wide ranging freshwater pumping scenarios. A Galerkin finite-element model considering sharp interface approach is used for this purpose. A semi-pervious subsurface barrier extending up to impervious bottom of the aquifer is considered at certain distance inland, parallel to the seacoast. The effect of barrier is analyzed in checking the advancement of the saltwater-freshwater interface under different scenarios of freshwater withdrawals at seaward and landward locations of the barrier and compared with nonbarrier conditions. The results indicated that barrier is able to check the advancement of the intrusion significantly and in certain cases, the progress is completely stalled for withdrawals on the landward side. Also, marked variations in the interface profile are observed as compared to no barrier condition, especially, for the seaward freshwater developments. From the model, nearest possible locations from the seacoast have been worked out for the safe withdrawal of freshwater where their effects are negligible on the saltwater advancement.     

Differential quantitation of surface and subsurface bacteria of normal skin by the combined use of the cotton swab and the scrub methods

By testing adjacent sites on the hypothenar eminence of the palm, enriched with bacteria by massaging the forehead, we found that the numbers of bacteria recovered from the skin surface by a wet cotton swab in 30 s were not significantly different from the numbers obtained by a brisk scrubbing with a blunted Teflon policeman for 120 s. This was true of aerobes (gram-positive cocci) and anaerobes (propionibacteria). If the same site on the palm was swabbed two times for 15 s each time, 67 to 94% of the total recovered bacteria were obtained on the first swab. Differential localization of bacteria into surface and subsurface populations was accomplished by first swabbing a test skin site to assay the surface flora and then scrubbing the same site to test for subsurface organisms. On the palm the swab yielded more aerobes and anaerobes than did the subsequent scrub. On the forehead the scrub yielded three to eight times as many anaerobes as the preceding swab. In some tests gram-positive cocci were distributed on the forehead like propionibacteria (large excess in scrub specimen); in other tests their numbers were similar in the swab and scrub specimens or there was a large excess in the swab specimen. These results indicate that there was no substantial subsurface flora on the palm. On the forehead propionibacteria were predominantly in deeper locations in all tests; gram-positive cocci were variable: in some test sites they were largely at the surface, whereas at other sites a predominance of cocci was in subsurface locations.     

Directing Exploration with 3D FEM Sensitivity and Data Uncertainty

Quantitatively directed exploration (QDE) employs a first-order Taylor series expansion to combine sensitivity of a 3D finite-element model (FEM) and uncertainty in geologic data to calculate the variance in project performance, which is employed to direct exploration. This approach is made practical by calculating model sensitivity with direct differentiation of the engineering analysis code, thus producing sensitivity with a single model run rather than multiple runs required by parameter perturbation. Uncertainty in subsurface data is computed through two different extrapolation methods for comparison: kriging and conditional probability (Bayesian updating). Although either of these methods can be employed in QDE, conditional probability is required to quantifiably terminate exploration. The QDE framework is applicable to any subsurface analysis that employs a 3D FEM. A case study illustrates the QDE approach, where settlement is the performance criterion, and layer interface elevations are the uncertain geologic data. Additional boring locations identified by QDE were placed where a combination of model sensitivity and subsurface uncertainty was the greatest, thus directing exploration toward the building footprint and away from existing sampled points.     

大方坯连铸42CrMoAH钢皮下夹杂物控制

 针对苏钢42CrMoAH钢大方坯（260mm×340mm）浇注存在的铸坯皮下夹杂物问题,分析了夹杂物的主要类型及其来源,研究了精炼渣组成对钢洁净度的影响,同时讨论了连铸工艺条件对铸坯皮下40mm以内的夹杂物数量、尺寸、组成的影响。研究表明：铸坯中的夹杂物主要来源于以A12O3为主的脱氧产物及以MnO·Cr2O3,FeO·Cr2O3等尖晶石类为主的二次氧化产物;由于精炼渣吸收A12O3夹杂物能力不足,再加上拉速低等因素导致结晶器内钢液上循环流弱,不利于脱氧及二次氧化产生的微小夹杂物在结晶器内碰撞聚合后上浮、排除,以致铸坯中尺寸为20~50μm的夹杂物达到总量的45%左右;采取提高精炼渣炉渣碱度、w(CaO)/w(Al2O3)值,及采用双侧孔型水口以加强结晶器内上循环流等措施后,铸坯皮下20~50μm的夹杂物降低了64%。     

New Orleans Levee System Performance during Hurricane Katrina: 17th Street Canal and Orleans Canal North

Centrifuge modeling of the 17th Street Canal and Orleans Canal North levees was performed in this study. During hurricane Katrina the levees on the 17th Street Canal failed, leading to breaches in the outfall canal in the city. Two mechanisms were observed in the centrifuge modeling that could cause a breach. First, a water-filled crack formed in front of the floodwall as the water in the canal rose above the top of the levee. The levees on the 17th Street Canal, which were supported on clay foundations, failed when this cracking led to a translational (sliding) failure in the clay layer commencing at the toe of the floodwall. The levees at Orleans Canal North, where failure did not occur, were also modeled to demonstrate that the model tests could successfully simulate failure and nonfailure conditions. The centrifuge model tests identified the importance of the crack formation in relation to the stability of the floodwall. These tests also confirmed that levee geometry, floodwall depth of penetration, and the underlying soil profile were all critical to the performance of the system under flood loading.     

Performance and Analyses of Mechanically Stabilized Earth Walls in the Tecomán, Mexico Earthquake

This paper discusses the performance and analysis of four mechanically stabilized earth (MSE) wall bridge approaches shaken by the 2003 Tecomán, Mexico earthquake. Strong shaking during the earthquake caused varying degrees of permanent displacement in several of the MSE walls. Immediately after the earthquake a geotechnical engineering reconnaissance team made detailed damage surveys of each wall. Complete design and construction data were later obtained. The analyses indicate that pullout of the upper reinforcement layers was the mechanism most likely responsible for the seismically induced deformation of the MSE walls. The upper layers of reinforcement were vulnerable to pullout because of the low levels of confining stress and the limited number of reinforcing elements per unit width. While pullout was the principal deformation mechanism, other factors contributing to deformation include large peak ground acceleration, more than twice the design value, and possible directional effects in the ground motion, which directed significant energy to the direction perpendicular to some of the walls. The latter finding concurs with observations made during the reconnaissance, where a clear directional bias was observed in the MSE wall deformations. The applicability and validity of the pseudostatic and sliding block methods of seismic analyses are discussed in light of the observed performance.     

An in vitro diffusion model for the study of calcification of bovine pericardium tissue

Bovine pericardium (BP) is extensively used for the production of heart valve bioprostheses. BP has excellent mechanical properties but a limited lifespan because of intrinsic subsurface calcification in vivo. In this study, the in vitro mineralization of BP was investigated by a novel diffusion cell model. In two sets of experiments, glutaraldehyde-treated BP membranes were placed between two compartments, both of which contained calcium phosphate solutions made by equilibration of octacalcium phosphate (Exp I) or dicalcium phosphate dihydrate (Exp II) in phosphoric acid. The movement of calcium (Ca), phosphate (P), and protons through the BP membrane was followed throughout the diffusion process. Histology, scanning electron microscopy, wet chemical analysis, and energy dispersive X-ray analyses provided good evidence of subsurface mineralization of BP that resembled in vivo mineral deposition. Energy dispersive x-ray microanalyses found a Ca/P heterogeneity of the early subsurface mineral that formed in the membrane. The use of a diffusion cell to model BP calcification under well-characterized conditions has led to in vitro mineralization that more closely matches that observed in vivo. The results suggest that this in vitro diffusion model can be used to study the mechanism of pathological mineralization. This model has the potential to provide rapid, inexpensive, basic information about the mineralization process.     

New Orleans Levee System Performance during Hurricane Katrina: London Avenue and Orleans Canal South

Hurricane Katrina was one of the worst natural disasters in U.S. history. The effects of the hurricane were particularly devastating in the city of New Orleans. Most of the damage was due to the failure of the levee system that surrounds the city to protect it from flooding. This paper presents the results of centrifuge models conducted at Rensselaer Polytechnic Institute and the U.S. Army Corps of Engineers simulating the behavior of the levees at London Avenue North and South that failed during Hurricane Katrina. Those levees failed without being overtopped by the storm surge. Also included are the results of a centrifuge model of one levee section at Orleans Canal South, which did not fail during the hurricane. The key factor of the failure mechanism of the London Avenue levees was the formation of a gap between the flooded side of the levee and the sheetpile. This gap triggered a reduction of the strength at the foundation of the protected side of the levee. The results are fully consistent with field observations.     

Levee Erosion by Overtopping in New Orleans during the Katrina Hurricane

Erodibility of a soil is defined here as the relationship between the erosion rate of a soil dz/dt and the velocity v of the water flowing over it, or the relationship between the erosion rate of a soil dz/dt and the shear stress developed by the water at the water-soil interface. This is called the erosion function. The test used to measure the erosion function of the levee soils is the erosion function apparatus test. The test consists of eroding a soil sample by pushing it out of a thin wall steel tube and recording the erosion rate for a given velocity of the water flowing over it. Several velocities are used and the erosion function is defined. A new erosion category chart is proposed to reduce the erodibility of a soil or rock to a single category number. Twenty three samples were retrieved from 11 locations at the surface of the levees around New Orleans. Thirteen were samples from Shelby tubes while ten were bag samples. The results obtained show a large variation of erosion resistance among the soils tested. Some of the levees associated with the location of the samples resisted the overtopping erosion very well; others eroded completely. On the basis of the erosion test results and of the observed behavior of the levees during the hurricane, a chart is presented which can be used to select soils for overtopping resistance. Numerical simulations were performed using the program CHEN 3D to obtain the distribution of velocity vectors in the overtopping flow and of shear stresses at the interface between the water and the levee surface. The comparison of the numerical simulation results and of the erosion function gives added credibility to the proposed levee overtopping erosion chart.     

Hydraulic Considerations in Geosynthetic and Aggregate Subsurface Drains

The hydraulic design of certain types of subsurface drains has recently been put on a more rational footing, and deficiencies in earlier design methods have been demonstrated. However, significant limitations remain in hydraulic design methods for geosynthetic and aggregate subsurface drains. It is important to decouple the groundwater hydrology from the internal hydraulics of the drain, and properly design subsurface drains for open-channel rather than pressurized conditions. Present design methods can inadvertently result in pressurized flow. The assumption of uniform flow (Manning’s equation alone) is also improperly made in some present design methods. Consequences can include unintended pressurized flow and attendant nonuniformity of inflow on the one hand and uneconomical design on the other. Current standard guidelines provide relatively little guidance for the design of geosynthetic and aggregate drains. A current ASTM standard, commonly referenced by geosynthetic manufacturers, has significant limitations. Deficiencies and qualifications are identified for present design methods. Guidance is given for the improved design of geosynthetic and aggregate subsurface drains based on sound hydraulic principles.     

Motions of alloying additions in the CAS steelmaking operations

Water model studies in a pilot scale ladle (D = 1.12 m andL = 0.93 m) were carried out to investigate the subsurface motion of both buoyant and sinking additions during the CAS (com-position adjustment by sealed argon bubbling systems) alloy addition procedure in steelmaking. This technique involves placing a refractory baffle around a rising gas/liquid plume within a stirred ladle of steel. Alloy additions are then made by projecting them into the slag-free region of steel within the baffled region. It was found that such particles while moving through the upwelling two-phase plume region can experience a significant reduction in drag forces, causing buoyant particles to penetrate more deeply than anticipated for a homogeneous fluid. Therefore, considering reduced drag on particles penetrating the upwelling gas liquid plume region, predictions were made for the trajectories of spherical-shaped particles using Newton’s law of motion. Predictions were in very reasonable agreement with those measured. Incorporating the velocity fields in industrial size vessels already reported by the present authors, trajectories of spherical-shaped additions (diameter ∼ 80 mm) in a 150-ton ladle during CAS operations were then predicted. The industrial implications of such trajectories, together with the alloy’s dissolution and dispersion behavior, were also analyzed. Finally, advantages of the CAS alloy addition procedure over conventional methods, in terms of the recovery rates of buoyant additions, are discussed.     

Heat Flow and Solidification Modeling of Industrial Scale,Ingot Casting Operation

A model, based on the concept of effective thermal conductivity, was developed to study thermal fields and the resultant solidification behavior of large, round, industrial size ingots. In this, flow and turbulence phenomena during mold filling as well as subsequent solidification were not modeled explicitly but their influence was accounted for by artificially raising the thermal conductivity of solidifying steel. Thus, a conduction like equation embodying a conjugate approach was applied to simultaneously predict the evolution of temperature fields in the mold as well as in the solidifying ingot following teeming. Prior to comparing model predictions against industrial scale measurements, sensitivity of calculations to grid size, time step height, convergence criterion etc. were rigorously assessed. Similarly, modeling of interfacial resistance, chemical reactions and heat effects in the hot top as well as their influence on predicted results were evaluated computationally. Embodying mixed thermal boundary conditions (free convection + radiation) at the mold wall, temperature fields during solidification of two different industrial large ingots were predicted numerically. Parallely, mold wall temperature was monitored as a function of time and surface temperature of ingot was measured at the instant of mold stripping using hand held, radiation pyrometers. Incorporating relevant operating conditions (viz., mold dimensions and size, ingot and hot top dimensions and material, initial mold and liquid temperature etc.) into the calculation scheme, predictions were made via a computational procedure developed in-house and results thus obtained were compared against equivalent industrial scale measurements. Very reasonable agreement between the two was demonstrated.     

Simplified Method for Spatial Evaluation of Liquefaction Potential in the St. Louis Area

As a part of an earthquake hazard mapping program being undertaken by the U.S. Geological Survey in the St. Louis metropolitan area, surficial geologic mapping and subsurface geotechnical data have been compiled into a three-dimensional geographic information system (GIS). The potential for soil liquefaction was then spatially evaluated by using subsurface information from 562 boreholes for an assumed M7.5 earthquake emanating from the New Madrid Seismic Zone. Geotechnical data (standard penetration test N-values, overburden pressure, and depth-to-groundwater) and the scenario peak ground accelerations (PGA = 0.1, 0.20, and 0.30??g) were applied to evaluate the factor of safety (FS) against earthquake-induced liquefaction. The liquefaction potential index (LPI) method was used in these evaluations because it allows for calculations of FS with depth for 10–25 discrete stratigraphic horizons overlying the bedrock across the St. Louis metropolitan area. LPI values were derived from the correlation between calculated LPI values and the depths-to-groundwater within late Quaternary stratigraphic units. The St. Louis metropolitan area was then classed according to four levels of severity of risk from liquefaction: (1)?no liquefaction potential, (2)?little-to-no likelihood, (3)?moderate, and (4)?severe.