Shotcrete support with special reference to Mexico City drainage tunnels

Summary The use of shotcrete is described as a structural support in tunnels in soft, waterbearing, semi-consolidated soil-rocks with an unconfined compressive strength ranging about 27 psi. The tunnels were 20–25 span at springline, widening to 56 in a transition section, 20–30 in height. Continuous water inflows of 25 litres/sec with surges to 50 litres/sec were experienced. No interior steel reinforcement was used in the transition section, though 3 m grouted bolts were used for rock reinforcement of the arch. Shear and tensile stresses slowly developed in the walls about the transition section, which were then bolted. In the face of waterinduced wall cavitations occurring in subsequent (20) tunnelling steel wire mesh was introduced in the shotcrete below springline. Abandoned for 12 months and left under water, floor heave of 20–30 cm developed, without damage to the shotcrete arch and walls. The inverts had been left open without lining.

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Zusammenfassung Die Anwendung von Spritzbeton als Ausbau von Wasserstollen in wenig festem, wasserhaltigem Fels mit unbeschränkter Druckfestigkeit von ungefähr 1,9 kp/cm² wird beschrieben. Die Stollen hatten eine Spannweite von 6 bis 8 m in Höhe der Mittellinie, die sich in einem Ausweitungsbereich bei einer Höhe von 6 bis 9 m bis auf 17 m vergrößerte. Ein ständiger Wasserzustrom von 25 l/s mit Schwallen bis 50 l/s wurde beobachtet. Im Ausweitungsbereich wurde kein innerer Stahlverbau benötigt, sondern es wurden 3 m lange, vorgemörtelte Bolzen zur Unterstützung des Felsens im Gewölbe verwendet. Scher- und Zugspannung entwickelten sich langsam in den Wänden des Übergangsbereiches, die dann geankert wurden. Im Hinblick auf Hohlraumbildungen durch Wassereinwirkung in den Wänden, die dem Ausbruch nachfolgend (6 m) entstanden, wurde ein Stahldrahtnetz unterhalb der Mittellinie in den Spritzbeton eingeführt. Geflutet und 12 Monate lang unter Wasser gelassen, entwickelte sich eine Bodenschwellung von 20–30 cm, ohne den Spritzbeton in den Wänden und im Gewölbe zu beschädigen. Die Sohlbögen wurden ohne Ausbau offen gelassen.

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Résumé On décrit l'emploi du béton projeté comme soutènement dans des roches semiconsolidées, meubles, et aquafères, dont la résistance à la compression simple est de l'ordre de 2 bar. Les tunnels ont 6 à 9 m de hauteur, 6 à 7,5 m de largeur aux naissances et jusqu'à 16 m dans les bifurcations. Le débit d'exhaure est 25 l/s avec des pointes à 50 l/s.On n'a pas employé d'armatures métalliques dans les bifurcations, mais on a renforcé le terrain de la voûte par des boulons injectés de 3 m de longueur. Des contraintes de cisaillement et de traction se sont lentement développées dans les piédroits des bifurcations, qui ont dû être boulonnés aussi.A l'avancement du tunnel après la bifurcation (en 6 m de large) l'écoulement de l'eau a provoqué des cavités dans les piédroits. On a alors ajoté du grillage au béton projeté au-dessous des naissances.Après un an d'abandon sans épuiser l'eau, le radier qui n'avait pas été revêtu s'est soulevé de 20 à 30 cm sans endommager la voûte ni les piédroits en béton projeté.

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With 13 Figures     

The externality fields of football grounds: a case study of the Dell, Southampton

Football grounds generate a negative externality — or nuisance— effect which, according to previous work, displays a distance decay pattern. However, on the basis of an exploratory investigation of the negative externality field produced by Southampton Football Club's ground it was found that the various elements which together comprise the general nuisance field varied both in intensity and in spatial extent. The noise nuisance, not surprisingly, is the most localized whilst the parked cars and traffic nuisances are the most extensive. In addition, whereas the specific nuisances of noise, pedestrians and ‘hooliganism’ each exhibit a distance decay pattern the incidence of the parked cars nuisance and, to a lesser extent, the traffic nuisance are less in the immediate vicinity of the ground than further away. Finally, despite the impression conveyed by the media, ‘hooliganism’ was perceived by local residents as much less of a football-generated nuisance than traffic congestion and parked cars.     

An Examination of the Oxidation of Elemental Mercury in the Presence of Halide Surfaces

Recent field investigations in polar regions, and over the ocean, have suggested that elemental mercury (Hg⁰) can be photochemically oxidized in the presence of reactive halogen species that are formed in the presence of salt particles, typically through a reactive catalytic cycle involving ozone destruction. Furthermore, these studies have suggested that the Hg⁰ oxidation reaction involves the reaction with reactive bromine species such as Br, BrO, and Br₂. To investigate these reactions in more detail, we performed experiments using a quartz reactive chamber so that the oxidation of Hg⁰, and the formation of ionic Hg products, could be examined in detail under different reaction scenarios, but at realistic levels of Hg. To examine if the reactions were enhanced by the presence of deliquescent salt surfaces, as has been postulated to be the case for the formation of reactive halogens, one surface of the cell was coated with either NaCl or NaBr for some experiments. In addition to laboratory experiments with a Xenon lamp, outdoor experiments under natural light were also conducted. The results of these studies showed that oxidation of Hg⁰ did not occur in the dark, except in the presence of a deliquescent NaBr salt surface. The rate of oxidation was slow in the absence of salt surfaces, and in the absence of low wavelength light (<324 nm). In the presence of NaCl surfaces, oxidation rates were at least two orders of magnitude faster, but the rate was further increased in the presence of NaBr, by a further factor of 25. With outdoor light, while the rates of oxidation were lower, the results were similar overall. The results are discussed in terms of the reactions occurring and the mechanisms of Hg⁰ oxidation. Finally, the implications of these reactions to the overall global Hg cycle are discussed.     

Gamma-ray bursts and Swift

Now that the Swift satellite is up and running, Paul O'Brien, Julian Osborne and Keith Mason report on the ideas and observations that this fast-moving autonomous observatory is investigating.     

Rotating Transition Region Features Observed with the SOHO Coronal Diagnostic Spectrometer

Strong evidence has been found from SOHO-CDS (Solar and Heliospheric Observatory – Coronal Diagnostic Spectrometer) observations to support the hypothesis that rotation plays a major role in the dynamics of transition region features. A comprehensive survey of the CDS daily synoptic rasters has been carried out to select dynamic events by searching for spectral line shifts in the Ov emission line at 629.73 Å (formed at a temperature of 2.5×105 K). Unique CDS observations of a macrospicule were reported by Pike and Harrison (1997), and several more macrospicule-like solar features have now been identified in the polar regions both on the limb and disk. These show blue- and red-shifted emission on either side of an axis stretching above the limb from a footpoint region on the disk. These observations are interpreted as indicating the presence of a rotating plasma, a sort of solar tornado. In the examples studied, the rotation velocities increase with height. The implications for coronal heating models are discussed.     

The Infrared Spectral Energy Distribution And Polarization Of Comet C/1995 O1 (Hale–Bopp) During 1997

Comets, such as C/1995 O1 (Hale-Bopp), are important to studies of the origins of the solar system because they are believed to be frozen reservoirs of the most primitive pre-solar dust grains and ices. Here, we report 1.2–18.5 μm infrared (IR) spectrophotometric and polarimetric observations of comet Hale-Bopp. Our measurements of the spectral energy distribution (SED) and IR polarization near perhelion passage suggest that emission from the coma was dominated by scattering and thermal emission from sub-micron sized dust grains. Hale-Bopp's surprising brightness may have been largely a result of the properties of its coma grains rather than the size of its nucleus. The thermal emission continuum from the grains had a superheat of S = T_color/T_BB ≥ 1.7, the peak of the 10 μm silicate emission feature was 1.7 mags above the carbon grain continuum, and the albedo (reflectivity) of the grains was ≥ 0.4 at a scattering angles, θ ≥ 135° This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of moult on crude oil load in a jackass penguin Spheniscus demersus

Induced moult has been suggested as a technique for rehabilitating oiled seabirds. An oiled jackass penguin underwent natural moult in captivity. Analyses of oil extracted from premoult and postmoult feathers indicate little qualitative difference, with significant amounts of oil transferred from premoult to postmoult feathers. Inducing moult, therefore does not appear to be viable for cleaning oiled seabirds.     

Genesis of copper mineralisation,Myall Creek prospect,South Australia

The Myall Creek copper prospect is in unmetamorphosed carbonaceous dolosiltstone and sandstone at the base of the late Proterozoic (Adelaidean) Tapley Hill Formation. It contains disseminated, fine-grained chalcopyrite, zincian tennanite, bornite, chalcocite, pyrite, sphalerite and galena, and irregular to straight chalcopyrite-rich veinlets. Some ore minerals rim and/or partially replace pyrite or clastic grains. There is no evidence of hydrothermal activity. The ³⁴S_CDT values of pyrite and the other sulfides fall in the wide range –3.6 to +44.2. Dolomite in both mineralised and unmineralised samples has ¹³C_PDB values concentrated around –3, and ¹⁸O_SMOW values around +25. It is concluded that the mineralising fluids were near-neutral brines which leached metals from the basement and early Adelaidean rocks. They entered the Tapley Hill sediments at moderately low temperatures via permeable strata and faults. The metals were precipitated by biogenic H₂S, and also fixed by reaction with iron sulfides and, possibly, organic matter. Continuing ascent of brines into the mineralised strata caused breakdown of detrital feldspars and Fe-Ti oxides, and some solution-remobilisation of early-formed sulfides.     

University Campuses and Housing Markets: Evidence from Nanjing

China has witnessed unprecedented growth of its universities in recent years. Because they function as a sort of urban quasi-public good, university campuses generate a variety of externalities within surrounding communities, including their impacts on adjacent housing markets. Through an analysis of the case of Nanjing, China, this study attempts to quantify the association between university campuses and housing markets in China and to help policymakers, planners, and community members better understand campus–community relationships more generally. The study yields the following findings. First, university campuses have been capitalized into the housing prices of their neighboring communities in Nanjing. Second, in the proximate communities, university campus spillover benefits involve trade-offs with the amenity values of other public goods. Third, campus capitalization effects vary across different tiers of universities. Based on the empirical results, we offer several policy implications, key among which are that policymakers need to acknowledge and rationally distribute the potential spillover benefits of the campus to multiple stakeholders; campus and residential communities should be planned synergistically to optimize land use efficiency; and universities should be fully engaged with their surrounding communities to maximize mutual benefits.