Triaxial strength of rock materials

SummaryTriaxial Strength of Rock Materials An attempt is made to define the nature and purposes of triaxial strength criteria, also to outline some factors to be considered in their selection and use.Seven alternative empirical strength criteria are compared on the basis of their simplicity and their fit to data for some fifteen hundred rock and concrete specimens. Two of these, one linear and one curved, are then compared in detail. Use of the curved rather than the linear criterion resulted in a significant reduction in strength prediction error.Methods of fitting the criteria to strength data are described. The parameters of the two criteria are then used to compare and classify rocks on the basis of their triaxial strength behaviour. Possible alternative formulations of the two criteria are considered in an appendix.

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ZusammenfassungDreiaxiale Festigkeit von Fels Es wird ein Versuch unternommen, Art und Zweck dreiaxialer Festigkeitskriterien zu bestimmen und einige derjenigen Faktoren zu ermitteln, die bei deren Auswahl und Anwendung von Bedeutung sind.Sieben verschiedene empirische Festigkeitskriterien werden nach ihrer Einfachheit und ihrer Übereinstimmung mit ungefähr 1500 Fels- und Betonproben verglichen. Zwei davon, eine linear und eine nicht linear, werden dann näher miteinander verglichen. Das nicht lineare Kriterium ergab, im Gegensatz zum linearen, eine bedeutende Verringerung des Fehlers in der Festigkeitsvorhersage.Methoden für die Anpassung der Kriterien an die Festigkeitsermittlungen werden beschrieben. Die Parameter der beiden Kriterien werden dann benützt, um Gesteine aufgrund ihres dreiaxialen Festigkeitverhaltens zu klassifizieren. Mögliche Alternativformulierungen der beiden Kriterien werden im Anhang behandelt.

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RésuméRésistance triaxiale de matériaux rocheux Une tentative est faite pour définir la nature et le but des critères de résistance triaxiale et aussi pour dégager les quelques facteurs devant être considérés pour leur choix et leur utilisation.Sept critères empiriques différents de résistance sont comparés sur le plan simplicité et concordance des mesures faites sur 1500 échantillons de roche et de béton. Deux de ces critéres, l'un linéaire, l'autre curviligne, sont ensuite comparés dans le detail. L'utilisation du critère curviligne plutôt que linéaire entraine une réduction notable de l'erreur dans la prédiction des résistances.Des méthodes d'ajustement des critères aux résistances mesurées sont décrites. Les paramètres des deux critères retenus sont ensuite utilisés pour comparer et classer les roches en fonction de leur comportement triaxial. En annexe, quelques autres possibilités de formulation des deux critères sont explicitées.

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With 7 Figures     

A global solution for the Mars static and seasonal gravity, Mars orientation, Phobos and Deimos masses, and Mars ephemeris

With the collection of six years of MGS tracking data and three years of Mars Odyssey tracking data, there has been a continual improvement in the JPL Mars gravity field determination. This includes the measurement of the seasonal changes in the gravity coefficients (e.g., , , , , , ) caused by the mass exchange between the polar ice caps and atmosphere. This paper describes the latest gravity field MGS95J to degree and order 95. The improvement comes from additional tracking data and the adoption of a more complete Mars orientation model with nutation, instead of the IAU 2000 model. Free wobble of the Mars' spin axis, i.e. polar motion, has been constrained to be less than 10 mas by looking at the temporal history of and . A strong annual signature is observed in , and this is a mixture of polar motion and ice mass redistribution. The Love number solution with a subset of Odyssey tracking data is consistent with the previous liquid outer core determination from MGS tracking data [Yoder et al., 2003. Science 300, 299-303], giving a combined solution of k₂=0.152±0.009 using MGS and Odyssey tracking data. The solutions for the masses of the Mars' moons show consistency between MGS, Odyssey, and Viking data sets; Phobos GM=(7.16±0.005)×¹⁰⁻⁴ km³/s² and Deimos GM=(0.98±0.07)×¹⁰⁻⁴ km³/s². Average MGS orbit errors, determined from differences in the overlaps of orbit solutions, have been reduced to 10-cm in the radial direction and 1.5 m along the spacecraft velocity and normal to the orbit plane. Hence, the ranging to the MGS and Odyssey spacecraft has resulted in position measurements of the Mars system center-of-mass relative to the Earth to an accuracy of one meter, greatly reducing the Mars ephemeris errors by several orders of magnitude, and providing mass estimates for Asteroids 1 Ceres, 2 Pallas, 3 Juno, 4 Vesta, and 324 Bamberga.     

El Niño-Southern Oscillation impacts on winter winds over Southern California

Changes in wintertime 10 m winds due to the El Niño-Southern Oscillation are examined using a 6 km resolution climate simulation of Southern California covering the period from 1959 through 2001. Wind speed statistics based on regional averages reveal a general signal of increased mean wind speeds and wind speed variability during El Niño across the region. An opposite and nearly as strong signal of decreased wind speed variability during La Niña is also found. These signals are generally more significant than the better-known signals in precipitation. In spite of these regional-scale generalizations, there are significant sub-regional mesoscale structures in the wind speed impacts. In some cases, impacts on mean winds and wind variability at the sub-regional scale are opposite to those of the region as a whole. All of these signals can be interpreted in terms of shifts in occurrences of the region’s main wind regimes due to the El Niño phenomenon. The results of this study can be used to understand how interannual wind speed variations in regions of Southern California are influenced by the El Niño phenomenon.     

绿色撒哈拉

占非洲面积将近三分之一的撒哈拉沙漠一度是热带稀树大草原,野生动植物种类丰富,充满鱼类的湖泊星罗棋布,而且有许多古人类生活在那里。“在约5 550~10 500年以前,撒哈拉是理想的生存地带,”斯特凡·克洛普林这样说过。克洛普林是德国科隆大学的地质考古学家,在过去的30年里,他     

Stones from Mohave County,Arizona: Multiple falls in the “Franconia strewn field”

One of the most productive and well‐sampled dense collection areas for meteorites on Earth is the “Franconia strewn field” in Mohave County, Arizona, which since 2002 has yielded hundreds of meteorites in an ellipsoidal area approximately 5 × 16 km across. Based on petrographic, mineral‐chemical, and terrestrial age data, we conclude that among 14 meteorites examined, there are at least 6 and possibly 8 distinct meteorites represented, which fell over a period of approximately 0–20 kyr ago. These include equilibrated H‐chondrites such as Franconia (H5) and Buck Mountains (BM) 001 (H6); H3–6 breccias such as Buck Mountains Wash and BM 004; and L6 chondrites such as BM 002 and BM 003 (which may be paired), Palo Verde Mine, and BM 005. To confidently pair such meteorites often requires thorough petrographic examination, mineral‐chemical analyses, and terrestrial ages. We estimate that 50 ± 10% of the larger specimens in this area are paired, yielding a relatively high value of approximately 2.3–2.9 distinct meteorites km^?2. The meteorite flux estimated for Franconia area is higher than the flux inferred from contemporary fireball data for larger masses. We suggest that one large H3–6 meteoroid fell in the area, most likely that of Buck Mountains Wash approximately 4 kyr ago, which produced an elliptical strewn field with masses generally increasing toward one end, and which raised the meteorite productivity in the recovery area.     

Whole Ecosystem Evidence of Eutrophication Enhancement by Wetland Dredging in a Shallow Tropical Lake

The purpose of this research was to assess the effects of dredging performed in a marginal wetland colonized by aquatic macrophytes on eutrophication of the adjacent shallow tropical lake (Imboassica Lake, Brazil). The river mouth of the Imboassica River that drains into Imboassica Lake had been densely colonized by aquatic vegetation dominated by Typha domingensis (Pers.) when it was dredged. Total and dissolved nitrogen and phosphorus concentrations were measured monthly over 13 years at four stations in the Imboassica river-lake system. Dredging activities reduced phosphorus and nitrogen retention at the river mouth and subsequently increased these nutrient stocks in the lake waters. Nutrient retention by non-dredged wetland was estimated to be ca. 1,200 kg year⁻¹ (87.3 g m⁻² year⁻¹) for nitrogen and 60 kg year⁻¹ (4.5 g m⁻² year⁻¹) for phosphorus. Our whole-lake approach suggested that dredging might intensify rather than mitigate eutrophication in shallow tropical lakes when the removal of aquatic macrophytes is coupled to the persistence of anthropogenic nutrient inputs from the watershed.