Dynamic response of flexible rockfall barriers under different loading geometries

Flexible steel barriers are commonly constructed on steep hillsides to mitigate rockfall. The evaluation of the dynamic response of proprietary flexible barriers is conventionally performed using full-scale field tests by dropping a weight onto the barriers in accordance with the European test standard ETAG 27. The weight typically has a spherical or polyhedral shape and cannot reproduce more complex rockfall scenarios encountered in the field. A rigid slab may load a barrier over a larger area and its effect has not been investigated. In this study, a calibrated three-dimensional finite-element model was developed to study the performance of vertically and horizontally orientated rockfall barriers under concentrated areal impact loads. A new bilinear force-displacement model was incorporated into the model to simulate the behavior of the energy-dissipating devices on the barriers. The effect of different weight geometries was studied by considering impacts by a rigid single spherical boulder and a rigid slab. Results reveal that areal loading induced by a rigid slab increases the loading on the barrier foundation by up to 40 % in both horizontally and vertically positioned barriers when compared to a concentrated load scenario with a single boulder. This indicates that barriers tested under the current test standard does not give the worst-case scenario in terms of foundation loads, and barrier designers should take into account the possible effect of increased foundation loads by reinforcing the barrier posts and/or increasing their spacing.     

Exploring the magnitude–frequency distribution: a cellular automata model for landslides

Landslide magnitude–frequency curves allow for the probabilistic characterization of regional landslide hazard. There is evidence that landslides exhibit self-organized criticality including the tendency to follow a power law over part of the magnitude–frequency distribution. Landslide distributions, however, also typically exhibit poor agreement with the power law at smaller sizes in a flattening of the slope known as rollover. Understanding the basis for this difference is critical if we are to accurately predict landslide hazard, risk or landscape denudation over large areas. One possible argument is that the magnitude–frequency distribution is dominated by physiographic controls whereby landslides tend to a larger size, and larger landslides are landscape limited according to a power law. We explore the physiographic argument using first a simple deterministic model and then a cellular automata model for watersheds in coastal British Columbia. The results compare favorably to actual landslide data: modeled landslides bifurcate at local elevation highs, deposit mass preferentially where the local slopes decrease, find routes in confined valley or channel networks, and, when sufficiently large, overwhelm the local topography. The magnitude–frequency distribution of both the actual landslides and the cellular automata model follow a power law for magnitudes higher than 10,000–20,000 m² and show a flattening of the slope for smaller magnitudes. Based on the results of both models, we argue that magnitude–frequency distributions, including both the rollover and the power law components, are a result of actual physiographic limitations related to slope, slope distance, and the distribution of mass within landslides. The cellular automata model uses simple empirically based rules that can be gathered for regions worldwide.     

Temporospatial dynamics and public health significance of bacterial flora identified on a major leatherback turtle (Dermochelys coriacea) nesting beach in the Southern Caribbean

Grande Riviere beach, on the island of Trinidad, supports the largest nesting population of leatherback turtles in the Caribbean region. Throughout the nesting season, nests are naturally disturbed by newly nesting females, resulting in egg breakage and loss of some nest viability. This environment is ideal for the growth and proliferation of microorganisms. The range of bacterial flora present in beach sand and egg shells was examined, with emphasis on bacteria that may pose a threat to public and animal health. The extent to which the bacterial load and genera on the beach changed throughout the season was also assessed. Twenty‐five genera were identified, with Pseudomonas spp. found to be the most predominant environmental bacteria. Four genera identified possess zoonotic potential, while five additional genera are known to be of public and animal health significance. Distinct shifts in the density and distribution of bacteria were observed along the beach from early to peak nesting season. Shifts were seen across heavily traversed zones, thus highlighting the potential exposure threats posed to beach visitors and animals alike. Further studies aimed at speciating this population of bacteria, as well as isolating potential fungal pathogens may mitigate this threat. Identification of bacterial agents that are specifically pathogenic to leatherback turtles, turtle eggs, hatchlings and those who may interact with these animals will serve to enhance and guide efforts to better conserve this species and protect the health of all who visit this ecologically significant site.     

Astronomical tuning of the Tortonian 87Sr/86Sr curve in the Mediterranean basin

ABSTRACT This work presents a detailed ⁸⁷Sr/⁸⁶Sr isotope curve for the interval 7.5–9.7 Ma obtained by a high-resolution analysis (sampling spacing of about 40 kyr) of an astronomically calibrated land-based sedimentary sequence exposed in the central Mediterranean area (Gibliscemi section, southern Sicily). The main aim is to verify a synchronous response of the Mediterranean seawater Sr isotope record to the oceanic forcing on the basis of multiple comparisons of the Gibliscemi record with published coeval ⁸⁷Sr/⁸⁶Sr curves. A good correlation with the ⁸⁷Sr/⁸⁶Sr data from the ODP site 926 (equatorial Atlantic ocean), considered to be the Sr chemostratigraphic reference section for the Late Miocene, and from the Pacific DSDP site 590B was registered. Conversely, the comparison of the Gibliscemi Sr isotope data with ⁸⁷Sr/⁸⁶Sr ratios from the coeval segment of the land-based Sardella section (eastern Mediterranean) shows important differences highlighting a local control on the seawater Sr isotope changes in semi-isolated subbasins within the Late Miocene Mediterranean.     

Thermal modeling of a Swiss urban aquifer and implications for geothermal heat pump systems

The progressive electrification of the building conditioning sector in recent years has greatly contributed to reducing greenhouse gas emissions by using renewable energy sources, particularly shallow geothermal energy. This energy can be exploited through open and closed shallow geothermal systems (SGS), and their performances greatly depend on the ground/groundwater temperature, which can be affected by both natural and anthropogenic phenomena. The present study proposes an approach to characterize aquifers affected by high SGS exploitation (not simulated in this work). Characterization of the potential hydro/thermogeological natural state is necessary to understand the regional flow and heat transport, and to identify local thermal anomalies. Passive microseismic and groundwater monitoring were used to assess the shape and thermal status of the aquifer; numerical modeling in both steady-state and transient conditions allowed understanding of the flow and heat transport patterns. Two significant thermal anomalies were detected in a fluvio-glacial aquifer in southern Switzerland, one created by river water exfiltration and one of anthropogenic nature. A favorable time lag of 110 days between river and groundwater temperature and an urban hot plume produced by underground structures were observed. These thermal anomalies greatly affect the local thermal status of the aquifer and consequently the design and efficiency of current and future SGS. Results show that the correct characterization of the natural thermo-hydrogeological status of an aquifer is a fundamental basis for determining the impact of boundary conditions and to provide initial conditions required to perform reliable local thermal sustainability assessments, especially where high SGS exploitation occurs.

     

Jack fracturing technique of stress measurement

SummaryJack Fracturing Technique of Stress Measurement This paper suggests a new approach for determining the initial state of stress in rock masses by strain relief measurements without overcoring.The method involves impressing friction-strain gauges on two opposite quadrants of a borehole wall, then uniaxially loading the other two quadrants with a self-equilibrating pair of forces of sufficient magnitude for initiating and propagating fractures of depth adequate to relieve strain. The initial tangential strains on the borehole wall are relieved by the creation of an open axial fracture and measured by the impressed friction gauges.Strain relief by borehole jack-fracturing was studied with finiteelement analysis and also by simple consideration of boundary conditions and external tractions. The dependence of the initial state of stress on the strain-relief measurements at different orientations is obtained by employing the classical theory of elasticity.The instrumentation unique to the method, a borehole-loading device and a friction-strain-gauge module, were tested in the laboratory, and the results summarized. Field-stress measurements made in a sandstone quarry for the magnitude and orientation of the stresses are in good agreement with those obtained by an independent overcoming technique. Work is progressing to compare results with a number of controlled cases.

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ZusammenfassungJack-Frakturing-Technik zur Spannungsmessung Es wird eine neue Methode zur Feststellung des Anfangsspannungszustandes in Steinmassen durch Messung der Verringerung der Belastung vorgestellt.In dieser Methode werden Reibungs-Dehnungs-Meßgeräte in zwei gegenüberliegende Quadrante einer Bohrlochwand gepreßt, und die anderen beiden Quadranten werden uniaxial belastet mit selbst-equilibrierenden Kräften, die groß genug sind, um Brüche zu verursachen. Die vorliegenden tangentialen Spannungen der Bohrlochwand werden durch das Erzeugen offener axialer Brüche gelöst und mit einem Reibungsmanometer gemessen.Belastungsminderung durch Bohrloch Jack-Brechung wurde mit finite-element analysis untersucht und ebenso durch einfache Anwendung der Grenzbedingungen. Die Abhängigkeit des Anfangsspannungszustandes von der Orientierung wird durch Anwendung der klassischen Elastizitätstheorie bewiesen.Die Bohrloch Spannungsapparatur und das Reibungs-Belastungsmanometer wurden im Laboratorium getestet. Messungen in Sandstein für die Größe und Orientierung der Spannungen liefern gute Übereinstimmung mit anderen Methoden.

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RésuméMéthode tube-fracture pour la détermination des constraintes Dans cet article, l'auteur suggère une nouvelle approche pour déterminer la contrainte initiale des masses rocheuses en mesurant le relâchement de la déformation sans avoir à percer la masse.Cette méthode consiste à imprimer sur deux quarts de cercle opposés des parois d'un tube cylindrique des indicateurs de la déformation causée par la friction; puis à contraindre latéralement les deux autres quarts de cercle avec deux forces qui s'équilibrent et qui ont une magnitude suffisante pour commencer et propager des fractures assez profondes pour que la déformation se relâche. Les contraintes tangentielles initiales sur la paroi du tube sont relachées par la création d'une fracture ouverte; on les mesure grâce aux indicateurs de déformation.On commence le relâchement de la déformation du tube par fracture avec l'analyse de l'élément fini et aussi en prenant en considération les conditions limites et les tractions extérieures. En utilisant la théorie classique de l'élasticité, on obtient le rapport de l'état initial de contrainte sur la mesure du relâchement de la déformation à différents angles.Les instruments uniques à cette méthode — un appareil destiné à impressionner le tube, et un indicateur de déformation par la friction — ont été mis au point en laboratoire et on a tabulé les résultats. Les mesures de déformation faites dans une carrière de grès pour établir la magnitude et la direction des déformations sont en accord avec les résultats obtenus par une technique indépendante de precement. Les travaux se poursuivent en vue de comparer les résultats avec un certain nombre de cas contrôlés.

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With 9 Figures     

Volcanology and lava flow morpho-types from the Koyna-Warna region,western Deccan Traps,India

Flow mapping and physical volcanology of 15 basaltic lavas exposed in three critical road pass sections (ghats) in the Koyna-Warna region of the western Deccan Traps is presented in this paper. Transitional lavas like rubbly pahoehoe are most common morpho-type exposed in these ghat sections. Sinking of rubbly breccia into flow interiors and formation of breccia-cored rosette are common in some lava flows. Few rubbly lavas exhibit slabby tendencies. The amount and nature of the associated rubble is variable and result from the mechanical fracturing and auto-brecciation of the upper vesicular crust in response to distinctive stages in the cooling, crystallization and emplacement history of individual lava flows. Occurrence of aa and pahoehoe morpho-types in the lava flow sequence is subordinate. Three prominent pahoehoe flows separated by red bole horizons are seen in the upper parts of the Kumbharli ghat. These are thick, P-type sheet pahoehoe. The pahoehoe lavas represent compound flow fields that grew by budding, endogenous lava transfer and inflation. Presence of pahoehoe lavas in the Koyna-Warna region hints at possible hitherto unrecorded southern extension of Bushe-like flow fields. This study reconfirms the existence of pahoehoe-slabby-rubbly-aa flow fields and transitions even in the upper echelons of the Deccan Trap stratigraphy. The study of morphology and internal structure of lava flows exposed at the ghat sections in the Koyna-Warna region could guide subsurface core-logging that is critical in deciphering the physical volcanology and emplacement dynamics of basaltic lava flows penetrated by drill holes sunk under the scientific deep drilling programme.     

Two in one leachate plume in a karstic aquifer

Some sites formerly used for waste disposal purposes, even if they are closed, continue generating leachate that seeps into the ground and contaminates groundwater in the area where they are located. It is believed that the rainfall being in contact with waste becomes a source of leachate. This fluid seeps into the aquifer and may identify sources of pollution. A modeling work which determined the migration times of solutes in the karstic aquifer of Merida, Yucatan, Mexico, is presented. Both existing and generated information was analyzed; a leachate plume was identified. The methodology used in the study is described, the application of which allowed concluding that this plume was generated from two sources: a waste disposal site and the oxidation lagoons located next to it. The procedure consisted of performing simulations considering the sources that contribute to the development of the pollution plume and forecasting their behavior. With the developed methodology, similar cases can be analyzed to avoid locating catchment zones of drinking water in inappropriate places and/or develop projects to place waste disposal sites that could affect existing catchment areas and to preserve this resource, essential for life.