Etude des Déformations et Inclinaisons du Sous-sol: Développements Instrumentaux et Applications dans la Région Sismique d’Arette,France

We present a modified version of a tilt and strain meter conceived to have great sensibility and good stability. These instruments were deployed in a cave at the seismic Pyrenean region of Arette (France). We set in evidence several types of phenomena, of which deformations brought about by water recharge filling up fissures on the massif are of importance. Owing to the redundance in the data, the study of the co-seismic deformations allows one to separate instrumental displacements and local readjustments from regional motions.     

Numerical analyses of deformability tests in jointed rock — “Joint Perturbation” and “No Tension” Finite Element solutions

SummaryNumerical Analyses of Deformability Tests in Jointed Rock — Joint Perturbation and No Tension Finite Element Solutions Sound design of structures in or upon rock requires a thorough knowledge of the rock mass deformability. Field test data interpretation has generally relied upon analytical or Finite Element linear elastic solutions. However, when testing in jointed rock, these can no longer be readily used since the medium cannot resist the tension induced upon loading. Accordingly, other solutions are required. If the discontinuities of the rock mass can all be mapped and their surface properties determined, the Finite Element model will use a Joint Perturbation solution where the joint elements have variable stiffnesses to account for movements along the fractures. If the discontinuities cannot be satisfactorily mapped, a global approach is provided by a No Tension analysis of the stress transfer type. The two techniques are compared in the case of bore hole jack deformability tests and found to agree remarkably well, indicating an appreciable difference from results of linear elasticity.

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ZusammenfassungNumerische Analyse von Verformungsversuchen in geklüfteten Fels — Lösungen mittels Kluft-Perturbation und No Tension Analysis auf Grund der Methode der Finiten Elemente Der Entwurf von Bauwerken in oder auf Fels erfordert eine genaue Kenntnis des Formänderungsverhaltens der Felsmasse. Im allgemeinen basiert die Interpretation der Ergebnisse von Feldversuchen auf den Lösungen des zugehörigen Randwertproblems der linearen Elastostatik mittels klassischer analytischer Methoden oder der Methode der Finiten Elemente. Wenn die Versuche aber in geklüftetem Fels durchgeführt werden, müssen die theoretischen Methoden modifiziert werden, da das Medium keine Zugspannungen aufnehmen kann. Zwei Fälle können unterschieden werden. Erstens: die Kluftflächen der Felsmasse können geometrisch erfaßt und ihre Oberflächeneigenschaften können bestimmt werden; in diesem Falle kann die Finite-Elemente-Lösung eine Kluft-Perturbations-Methode verwenden, in welcher spezielle Kluft-Elemente verschiedener Steifigkeiten normal und tangential zu den Kluftflächen die Bewegungen entlang derselben bestimmen. Zweitens: die Diskontinuitäten der Felsmasse können nicht hinreichend beschrieben werden; für diesen Fall ist vorgekehrt durch die Finite-Element-Analyse vom Typ der Spannungsumlagerung unter Ausschaltung der Zugspannungen (No Tension Analysis), um das globale Verhalten der geklüfteten Felsmasse zu erfassen. Die Lösungen dieser beiden Methoden wurden für den Fall der Bohrloch-Verformungs-Tests verglichen; der Vergleich zeigt ausgezeichnete Übereinstimmung, im Gegensatz zu den Lösungen als lineares Elastizitätsproblem.

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RésuméLa méthode des Eléments Finis appliquée aux résultats d'essais de vérins cylindriques dans les roches fissurées — solutions dites Joint Pertubé et Sans Traction La construction de structures sur ou dans des roches nécessite une connaissance approfendie de la déformabilité du massif rocheux. L'analyse des résultats d'essais en place se fait généralement à l'aide de solutions analytiques ou par Eléments Finis, qui supposent une élasticité linéaire du milieu. De fait, dans les roches fissurées, ces solutions sont inadéquates puisque le milieu ne peut résister aux sollicitations de traction. Il s'agit donc d'utiliser d'autres méthodes d'analyse. Lors qu'il est possible de déterminer la géométrie et les propriétés de toutes les discontinuités, l'on pourra utiliser une solution par Eléments Finis, dite Joint Perturbé dans laquelle la rigidité de surface du joint (ou fissure) peut varier lorsque des movements prennent place au niveau du joint. Si cela est impossible, il faudra utiliser une approche globale dite Sans Traction qui redistribue les contraintes de traction et les dissipe. On compare ces deux types de solutions dans le cas des essais de vérins cylindriques unidirectionnels. Leurs résultats sont identiques et ont nettement différents de ceux obtenus avec une solution élastique linéaire.

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Research supported by the National Aeronautics and Space Administration — Contract NAS 8-21432.

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With 8 Figures     

Seeing Conditions at Sutherland. Results of the 1992/93 seeing campaign

In order to decide whether the seeing conditions at SAAO/Sutherland justify the erection of a 3.5 m telescope and also to compare Sutherland with the Gamsberg/Namibia site, a seeing campaign covering 15 months has been carried out. For direct comparison with the results of the seeing campaign at Gamsberg twenty years before the same QUESTAR telescope was employed. The seeing is determined by the scattering of the star-trail exposed on a film in the focal plane of the telescope. The campaign commenced in February 1992. Up to May 1993, data for 204 nights, that is 47.3% of the total number of nights, were collected. Due to wind speeds above 30 km h^-1, 25 out of the 204 nights were not considered in the final reduction. The useful 179 nights are evenly distributed over the campaign period. The median seeing value for the whole period is = 0.52. There are differences during the year: the best season gives = 0.42, the worst = 0.67. Each night was divided into three intervals, although data for each of the three intervals were not always available. Generally, there is an improvement in the seeing during the course of a night. The results are compared to the seeing values of Gamsberg/Namibia and ESO/La Silla.     

Finite element models for rock fracture mechanics

A finite element model for the prediction of discrete fracture propagation in rock structures loaded in compression is presented. The model integrates any one of three theories for mixed-mode fracture initiation; it contains an energy balance algorithm for predicting crack increment length, and incorporates recent developments in finite element stress-intensity factor computation. The predictions of the model are compared with the observed fracture response of a real rock structure. Results show that the model accurately predicts both stable and unstable fracture progagations observed experimentally.     

Radiation pressure and dust particle dynamics

The dynamics of small dust grains orbiting a planet are investigated when solar radiation pressure forces are added to the planet's gravitational central field. In the first part a set of differential equations is derived in a reference frame linked to the solar motion. The complete solution of these equations is given for particles lying in the planet's orbital plane, and we show that the orbital eccentricity may undergo considerable variation. At the same time the pericenter longitude librates or circulates according to initial conditions. With this result we establish a criterion for any orbiting particle (because of its highly eccentric orbit) to collide with its planet's atmosphere. The case of inclined orbit is studied through a numerical integration and allows us to draw conclusions related to the stability of the orbital plane. All solutions are periodic, with the period being independent of the initial conditions. This last point permits us to investigate the different time scales involved in that problem. Finally, the Poynting-Robertson drag is included, along with the radial radiation pressure forces, and the secular trend is considered. A coupling effect between the two components is ascertained, yielding a systematic behavior in the eccentricity and thus in the pericenter distance. Our solutions generalize the results of S. J. Peale (1966, J. Geophys. Res.71, 911–933) and J. A. Burns, P. Lamy, and S. Soter (1979, Icarus40, 1–48) by allowing eccentricities to be large (of order 1) and inclinations to be nonzero and by considering Poynting-Robertson drag.     

51 Peg and Upsilon and: Confirmation of the Planet Hypothesis

Earth, Moon, and Planets -     

Laboratory sulfurisation of the marine microalga Nannochloropsis salina

To understand more fully the mode of preservation of organic matter in marine sediments, laboratory sulfurisation of intact cells of the cultured microalga Nannochloropsis salina was performed using inorganic polysulfides in seawater at 50°C. Solvent extractable and non-extractable materials were analysed by GC–MS and Py–GC–MS, respectively, to study the incorporation of sulfur into the microalgal organic matter. No GC-amenable sulfur-containing compounds were found in the extracts apart from some minor thiophenes with a phytanyl carbon skeleton. The residue after extraction and hydrolysis contained abundant macromolecular sulfur-containing moieties as revealed by the presence of dominant C₂₈–C₃₂ thiols, thiophenes, thianes and thiolanes in the flash pyrolysates. These products are thought to be formed from moieties derived from sulfurisation of C₂₈–C₃₂ diols and alkenols, characteristic lipids of N. salina. C₁–C₂ alkylated thiophenes were also found in the pyrolysates and probably result from moieties formed upon sulfurisation of carbohydrates. The highly resistant biomacromolecule (algaenan) synthesised by N. salina remains unaffected by sulfurisation. The non-hydrolysable residue isolated from the sulfurised N. salina thus comprises algaenan and (poly)sulfide-bound long alkyl chains. The sulfurisation experiments show that both selective preservation of algaenans and lipid and carbohydrate “vulcanisation” can be involved in the preservation of algal organic matter in marine environments.     

Scale effects in the determination of rock mass strength and deformability

SummaryScale Effects in the Determination of Rock Mass Strength and Deformability An extensive literature search was conducted, to investigate the effect of the scale of testing on the measurement of strength and stiffness of rock masses. The results are presented for bearing capacity tests, compression tests, and several types of deformability tests.Field strength values are generally several times smaller than laboratory values. Field moduli generally appear to be between 20 per cent to 60 per cent of laboratory measured moduli.All strength and deformability results reviewed point to the great need for more field tests. Specific suggestions are given.

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ZusammenfassungMastabeffekte bei der Bestimmung mechanischer Eigenschaften von Fels Ein eingehendes Literaturstudium wurde durchgeführt, um den Maßstabeffekt auf die Festigkeits- und Verformbarkeitsmessungen im Fels zu untersuchen. Es werden Resultate von Plattendruckversuchen, Druckversuchen und mehreren Verformungsversuchen aufgeführt. Die in-situ gemessene Festigkeit ist im allgemeinen ein Bruchteil derjenigen, die bei Laborversuchen festgestellt wird. Die Verformbarkeiten in-situ betragen meistens 20 bis 60 Prozent der im Labor erhaltenen Werte. Alle Resultate zeigen, daß mehr In-situ-Versuche notwendig sind. Der Autor macht dazu einige Vorschläge.

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RésuméL'effet d'échelle dans les mesures de propriétés mécaniques des massifs rocheux. On a fait une recherche bibliographique détaillée, pour étudier l'effet d'échelle sur les mesures de résistance et de déformabilité des masses rocheuses. On présente des résultats concernant les essais de résistance à la plaque, les essais de compression, et plusieurs types d'essais de déformabilité en place.Les résistances mesurées in-situ sont généralement une fraction de celles mesurées au laboratoire. Les déformabilités mesurées en place sont généralement entre 20 et 60 pour cent des valeurs au laboratoire.Tous les résultats que l'on a examiné indiquent la nécessité d'effectuer plus d'essais en place. L'auteur offre un certain nombre de suggestions.

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With 22 Figures     

Annual survey of water vapor behavior from the OMEGA mapping spectrometer onboard Mars Express

We present here the annual behavior of atmospheric water vapor on Mars, as observed by the OMEGA spectrometer on board Mars Express during its first martian year. We consider all the different features of the cycle of water vapor: temporal evolution, both at a seasonal and at a diurnal scale; longitudinal distribution; and the vertical profile, through the variations in the saturation height. We put our results into the context of the current knowledge on the water cycle through a systematic comparison with the already published datasets. The seasonal behavior is in very good agreement with past and simultaneous retrievals both qualitatively and quantitatively, within the uncertainties. The average water vapor abundance during the year is ∼10 pr. μm, with an imbalance between northern and southern hemisphere, in favor of the first. The maximum of activity, up to 60 pr. μm, occurs at high northern latitudes during local summer and shows the dominance of the northern polar cap within the driving processes of the water cycle. A corresponding maximum at southern polar latitudes during the local summer is present, but less structured and intense. It reaches ∼25 pr. μm at its peak. Global circulation has some influence in shaping the water cycle, but it is less prominent than the results from previous instruments suggest. No significant correlation between water vapor column density and local hour is detected. We can constrain the amount of water vapor exchanged between the surface and the atmosphere to few pr. μm. This is consistent with recent results by OMEGA and PFS-LW. The action of the regolith layer on the global water cycle seems to be minor, but it cannot be precisely constrained. The distribution of water vapor on the planet, after removing the topography, shows the already known two-maxima system, over Tharsis and Arabia Terra. However, the Arabia Terra increase is quite fragmented compared with previous observations. A deep zone of minimum separates the two regions. The saturation height of water vapor is mainly governed by the variations of insolation during the year. It is confined within 5-15 km from the surface at aphelion, while in the perihelion season it stretches up to 55 km of altitude.