Earthquake Induced Excess Pore Water Pressures in the Upper San Fernando Dam During the 1971 San Fernando Earthquake

The excess pore water pressure developed in the Upper San Fernando Dam during the 1971 San Fernando Earthquake has been evaluated in several studies. Almost all of these studies indicate large excess pore pressure ratios developed only in the upstream and downstream shells which are not consistent with the limited deformation of the dam and the piezometer responses during the earthquake. In this paper, the construction and field observations of the behavior of the Upper San Fernando Dam are reviewed and a simple approach involving Newmark’s (1965) and Makdisi-Seed’s (1978) permanent deformation and limit equilibrium slope stability analyses are used to estimate the excess pore water pressures developed in the core and downstream shell areas during the earthquake for comparison with field measurements. The major differences of this analysis with previous studies lies in the assumptions regarding the selection of the failure plane, liquefiable zones, and mobilized shear strengths. The results explain the field piezometric observations and the limited displacement of the dam

Case Study: Unsaturated Embankment Failure on Soft Soils

This paper describes the application of unsaturated soil mechanics to an interstate connecting-ramp embankment that failed during construction. Specifically, matric suction is incorporated into the calculation of the tension crack (TC) depth induced by desiccation and strain incompatibility and the contribution of matric suction to embankment shear strength. The results are compared with field observations to assess the viability of unsaturated soil mechanics in modeling compacted embankments in stability analyses. Results from this study suggest that using unsaturated shear strength parameters while introducing a TC in the compacted fill yields a reasonable inverse analysis of this interstate embankment. This may be preferred in slope stability analyses to the current practice of using an undrained shear strength (i.e., cohesion) for the unsaturated compacted fill and including a TC to generate a reasonable factor of safety

Back-Analyses of Landfill Slope Failures

This paper investigates the shear strength of municipal solid waste (MSW) using back analyses of failed waste slopes. Shear strength of MSW is a function of many factors such as waste type, composition, compaction, daily cover, moisture conditions, age, decomposition, overburden pressure, etc. These factors together with non-standardized sampling methods, insufficient sample size to be representative of in-situ conditions, and limited shear displacement or axial strain imposed during the shear tests affect the test results and have created considerable scatter in reported test results. This scatter led the authors to pursue the back-analysis of failed waste slopes as a better means for estimating the shear strength of MSW. The back-analysis of failed waste slopes in the Gnojna Grora landfill in Poland, Istanbul Landfill in Turkey, Hiriya Landfill in Israel, and Payatas Landfill in Philippines are presented in this paper. Each of the landfill slope failures is reviewed and the results of the back-analyses presented. Finally, comparison of the recommended shear strength envelope of MSW and those by various researchers for the design of landfill slopes is presented

Liquefaction Analysis of Lower San Fernando Darn Using Strength Ratios

Olson (2000) evaluated 33 liquefaction flow failure case histories to assess the yield strength ratio and liquefied strength ratio mobilized during the failures. Using back-analysis procedures developed by Olson (2000), yield and liquefied shear strengths are shown to be proportional to the pre-failure vertical effective stress and are related to standard and cone penetration resistances. This paper examines the triggering of liquefaction and subsequent flow failure of Lower San Fernando Dam using yield and liquefied strength ratios. The yield strength ratio is used to correctly predict the occurrence of liquefaction in the upstream hydraulic fill of the dam, and the liquefied shear strength ratio is used to correctly predict the subsequent flow failure of the upstream slope. The relationships for the yield and liquefied ratios are presented, and their application to existing or new structures is illustrated using the Lower San Fernando Dam case history

Back-analysis of Preexisting Landslides

ABSTRACT Drained residual shear strength is applicable to slopes containing preexisting shear surfaces and preexisting landslides. Laboratory ring shear testing by various researchers suggest the possibility of strength gain along preexisting shear surfaces which had previously obtained a residual strength condition. This paper presents back-analysis of two case histories that were used to suggest strength recovery to confirm test results developed herein and explain how the recovered strength may be useful in understanding slope behavior during the rest period and movement reactivation. These back-analyses are important to determine whether or not strength gain occurs and the practical significance, if any, of the strength gain in design of the remedial measures

Interdependencies Between Wildfire-Induced Alterations in Soil Properties, Near-Surface Processes, and Geohazards

The frequency, severity, and spatial extent of destructive wildfires have increased in several regions globally over the past decades. While direct impacts from wildfires are devastating, the hazardous legacy of wildfires affects nearby communities long after the flames have been extinguished. Post-wildfire soil conditions control the persistence, severity, and timing of cascading geohazards in burned landscapes. The interplay and feedback between geohazards and wildfire-induced changes to soil properties, land cover conditions, and near-surface and surface processes are still poorly understood. Here, we synthesize wildfire-induced processes that can affect the critical attributes of burned soils and their conditioning of subsequent geohazards. More specifically, we discuss the state of knowledge pertaining to changes in mineralogical, hydraulic, mechanical, and thermal properties of soil due to wildfire with a focus on advances in the past decade. We identify how these changes in soil properties alter evapotranspiration, interception, sediment transport, infiltration, and runoff. We then link these alterations to the evolution of different geohazards, including dry raveling, erosion, rockfalls, landslides, debris flows, and land subsidence. Finally, we identify research gaps and future directions to advance knowledge on how wildfires control the evolution of various earth surface processes and geohazards over time

Large-scale, high-density (up to 512 channels) recording of local circuits in behaving animals

Monitoring representative fractions of neurons from multiple brain circuits in behaving animals is necessary for understanding neuronal computation. Here we describe a system that allows high channel count recordings from a small volume of neuronal tissue using a lightweight signal multiplexing head-stage that permits free behavior of small rodents. The system integrates multi-shank, high-density recording silicon probes, ultra-flexible interconnects and a miniaturized microdrive. These improvements allowed for simultaneous recordings of local field potentials and unit activity from hundreds of sites without confining free movements of the animal. The advantages of large-scale recordings are illustrated by determining the electro-anatomical boundaries of layers and regions in the hippocampus and neocortex and constructing a circuit diagram of functional connections among neurons in real anatomical space. These methods will allow the investigation of circuit operations and behavior-dependent inter-regional interactions for testing hypotheses of neural networks and brain function

Modified Standard Penetration Test–based Drilled Shaft Design Method for Weak Rocks

In this project, Illinois-specific design procedures were developed for drilled shafts founded in weak shale or rock. In particular, a modified standard penetration test was developed and verified to characterize the in situ condition of weak shales or rocks in Illinois for drilled shaft design. For this project, weak shale or rock is defined as an intermediate geologic material (IGM) with an unconfined compressive strength of 10 to 100 ksf. These investigation and design improvements are anticipated to lead to safer deep-foundation design and reduced costs for IDOT.IDOT-R27-145Ope

Probing for Exoplanets Hiding in Dusty Debris Disks: Disk Imaging, Characterization, and Exploration with HST/STIS Multi-Roll Coronagraphy

Spatially resolved scattered-light images of circumstellar (CS) debris in exoplanetary systems constrain the physical properties and orbits of the dust particles in these systems. They also inform on co-orbiting (but unseen) planets, systemic architectures, and forces perturbing starlight-scattering CS material. Using HST/STIS optical coronagraphy, we have completed the observational phase of a program to study the spatial distribution of dust in ten CS debris systems, and one "mature" protoplanetrary disk all with HST pedigree, using PSF-subtracted multi-roll coronagraphy. These observations probe stellocentric distances > 5 AU for the nearest stars, and simultaneously resolve disk substructures well beyond, corresponding to the giant planet and Kuiper belt regions in our Solar System. They also disclose diffuse very low-surface brightness dust at larger stellocentric distances. We present new results inclusive of fainter disks such as HD92945 confirming, and better revealing, the existence of a narrow inner debris ring within a larger diffuse dust disk. Other disks with ring-like sub-structures, significant asymmetries and complex morphologies include: HD181327 with a posited spray of ejecta from a recent massive collision in an exo-Kuiper belt; HD61005 suggested interacting with the local ISM; HD15115 & HD32297, discussed also in the context of environmental interactions. These disks, and HD15745, suggest debris system evolution cannot be treated in isolation. For AU Mic's edge-on disk, out-of-plane surface brightness asymmetries at > 5 AU may implicate one or more planetary perturbers. Time resolved images of the MP Mus proto-planetary disk provide spatially resolved temporal variability in the disk illumination. These and other new images from our program enable direct inter-comparison of the architectures of these exoplanetary debris systems in the context of our own Solar System.Comment: 109 pages, 43 figures, accepted for publication in the Astronomical Journa

Nighttime removal of NOx in the summer marine boundary layer

The nitrate radical, NO3, and dinitrogen pentoxide, N2O5, are two important components of nitrogen oxides that occur predominantly at night in the lower troposphere. Because a large fraction of NO2 reacts to form NO3 and N2O5 during the course of a night, their fate is an important determining factor to the overall fate of NOx (=NO and NO2). As a comprehensive test of nocturnal nitrogen oxide chemistry, concentrations of O3, NO, NO2, NO3, N2O5, HNO3 and a host of other relevant compounds, aerosol abundance and composition, and meteorological conditions were measured in the marine boundary layer from the NOAA research vessel Ronald H. Brown off the East Coast of the United States as part of the New England Air Quality Study (NEAQS) during the summer of 2002. The results confirm the prominent role of NO3 and N2O5 in converting NOx to HNO3 at night with an efficiency on par with daytime photochemical conversion. The findings demonstrate the large role of nighttime chemistry in determining the NOx budget and consequent production of ozone. INDEX TERMS: 0322 Atmospheric Composition and Structure: Constituent sources and sinks; 0345 Atmospheric Composition and Structure: Pollution—urban and regional (0305); 0365 Atmospheric Composition and Structure: Troposphere—composition and chemistry. Citation: Brown, S. S., et al. (2004), Nighttime removal of NOx in the summer marine boundary layer, Geophys. Res. Lett., 31, L07108, doi:10.1029/2004GL01941