Analysis of the dynamic behaviour of the hangingwall beam during a seismic event

Bibliography: leaves 68-72.In a deep-level gold mine planes of weakness oriented parallel to the reef allow the hangingwall to separate from adjacent rock strata. The hangingwall then acts as a separate beam supporting only its selfweight. Mining-induced near vertical shear fractures divide the hangingwall beam into distinct blocks of relatively intact material. The objective of this study is to investigate the response of the isolated hangingwall beam during a seismic event. The study is particularly concerned with the global, resonant behaviour of the hangingwall and local shear or crushing failure of the rock at the shear fractures is not considered. A finite element program is developed to compute the hangingwall response during seismicity. The response is normalised, thus permitting the response spectrum method to describe maximum hangingwall motions during a seismic event at various beam lengths. By comparing the response spectrum describing a single-degree-of-freedom (SDOF) system with the spectrum of the hangingwall, it is evident that, although the hangingwall response spectrum is shifted to a higher frequency and velocity domain, the shapes of the two spectra are essentially the same. The frequency and velocity shift is calculated for 15 seismic events and empirical rules are developed to quantify the spectral shift for a wide range of event magnitudes. Unlike the spectrum describing hangingwall motions, the construction of a SDOF response spectrum is computationally cheap and is standard practice in earthquake engineering. By applying the empirical rules the seismologist can extrapolate the SDOF spectrum to estimate maximum hangingwall motions due to a seismic event and critical beam lengths which are prone to resonance. The effect on the response of the hangingwall supported by backfill consisting of dewatered and cemented tailings is evaluated. It is shown that a fill-to-face lag of less than 5m reduces hangingwall motions considerably. Further, at small strains the stiffer cemented tailings provide superior support than that offered by comparatively soft dewatered tailings. A chart is presented which correlates event magnitudes to critical beam lengths prone to resonance

Introduction: Toward an Engaged Feminist Heritage Praxis

We advocate a feminist approach to archaeological heritage work in order to transform heritage practice and the production of archaeological knowledge. We use an engaged feminist standpoint and situate intersubjectivity and intersectionality as critical components of this practice. An engaged feminist approach to heritage work allows the discipline to consider women’s, men’s, and gender non-conforming persons’ positions in the field, to reveal their contributions, to develop critical pedagogical approaches, and to rethink forms of representation. Throughout, we emphasize the intellectual labor of women of color, queer and gender non-conforming persons, and early white feminists in archaeology

Isotopic composition of nitrate in five German rivers discharging into the North Sea

We determined concentrations and isotopic composition of nitrate in five German rivers (Rhine, Elbe, Weser, Ems, and Eider) that discharge into the North Sea. Samples were obtained on a biweekly to monthly basis and chemical and isotopic analyses were conducted for the period January 2006 to March 2007 at sampling stations situated before estuarine mixing with North Sea water. We observed maximum nitrate loads in winter and fall, when both discharge and concentration of nitrate are highest. Mean annual isotope values in nitrate ranged from 8.2% to 11.3% for delta(15)N NO(3)(-) and 0.4% to 2.2% for 6180 NO(3)(-). The ranges of isotope values suggest that nitrate in these rivers derives from soil nitrification, sewage, and/or manure. These and published data on other rivers in northern Europe and northern America reveal a correlation between agricultural land use (>60% in the catchment areas of rivers examined) and delta(15)N NO(3)(-) values. The rivers Rhine. Elbe, Weser and Ems show similar seasonal patterns of the isotopic fractionation of nitrate with increasing (delta(15)N NO(3)(-) values and simultaneously decreasing NO(3)(-) concentrations during summer months, indicating that assimilation of nitrate is the main fractionation process of riverine nitrate. Isotopic signals in winter are more depleted than the mean summer isotope values, attributed to less microbial activity and assimilative processes. Load weighted nitrate delta(15)N of the riverine input to the German Bight Coastal Water mass before estuarine mixing and processing is between 8% and 12%. The high delta(15)N value of river nitrate is matched by high delta(15)N of nitrate in surface sediments in the German Bight. (C) 2008 Elsevier Ltd. All rights reserved

Sub-recent nitrogen-isotope trends in sediments from skagerrak (North sea) and kattegat: Changes in N-budgets and N-sources?

We determined (15)N/(14)N ratios of total nitrogen in surface sediments and dated sediment cores to reconstruct the history of N-loading of the North Sea. The isotopic N composition in modern Surface sediments is equivalent to and reflects the isotopic mixture of oceanic nitrate on the one hand (delta(15)N=5 parts per thousand) and the imprint of river-borne nitrogen input into the SE North Sea (delta(15)N up to 12 parts per thousand in estuaries of the SE North Sea) on the other hand. We compare the results with 615 N records from pre-industrial sediment intervals in cores from the Skagerrak and Kattegat areas, which both constitute significant depositional centres for N in the North Sea and the Baltic Sea/North Sea transition. As expected, isotopically enriched anthropogenic nitrogen was found in the two records from the Kattegat area, which is close to eutrophication sources on land. Enrichment of delta(15)N in cores from the Skagerrak - the largest sediment sink for nitrogen in the entire North Sea - was not significant and values were similar to those found in sediment layers representing pre-industrial conditions. We interpret this isotopic uniformity as an indication that most riverine reactive nitrogen with its characteristic isotopic signature is removed by denitrification in shallow shallow-water sediments before reaching the main sedimentary basin of the North Sea. (C) 2008 Elsevier B.V. All rights reserved