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Early Silurian (Llandovery) graptolite assemblages of Saudi Arabia: biozonation, palaeoenvironmental significance and biogeography

Williams M., Zalasiewicz J., Boukhamsin H., Cesari C.

Geological Quarterly

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2016

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Vol. 60, No. 1

3--25

EN

Analysis of Silurian graptolite assemblages from 1017 sample horizons in 132 cores (from 65 boreholes) through the Qusaiba Member, Qalibah Formation of Saudi Arabia, provides a refined graptolite biostratigraphy for the Arabian Peninsula comparable in its resolution to that from the British Isles and the Czech Republic. Over 150 graptolite species characterize 11 biozones from the lowermost Rhuddanian lubricus Biozone to the lower Telychian guerichi Biozone, with sub-zonal resolution for several intervals. Graptolite biozonal boundaries and the Rhuddanian-Aeronian and Aeronian-Telychian stage boundaries can be placed with high precision. Detailed analysis of graptolite spatial distribution suggests persistent depth-stratified marine assemblages across the Silurian palaeo-Arabian Plate. Near-surface-dwelling assemblages probably occupied the mixed-layer of Silurian oceans, enabling colonization of shallow shelf environments. They are low-diversity (1-2 species) assemblages characterized by Neodiplograptus, Coronograptus, Neolagarograptus and Stimulograptus species and often are preserved in strata with extensive shelly faunas. Deeper marine assemblages are of higher diversity (up to 15 species per horizon), and are characterized by dorsally curved or helically coiled species of Spirograptus, Demirastrites, Lituigraptus, Rastrites and Torquigraptus. Recognition of depth-stratified graptolite assemblages provides an important tool for establishing palaeo-basin topography and water depth at the time of sedimentary deposition. At the species level, the graptolite assemblages of Saudi Arabia are remarkably similar to contemporaneous faunas from peri-Gondwanan Europe and, from the middle Rhuddanian onwards, also to the Avalonian and Laurentian Llandovery graptolites of the UK.

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Prediction of the failure mechanism of arches under base motion using DEM based on the NSCD method

Albuerne A., Williams M., Lawson V.

Wiadomości Konserwatorskie

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2013

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Nr 34

41--47

EN

Many historic structures are located in regions of significant seismic activity and are vulnerable to earthquake damage. To assess the safety of these structures, an understanding of the seismic performance of key elements such as masonry arches, vaults and domes is vital. While static stability of masonry arches can be studied analytically using the principles of limit analysis, numerical methods are needed to deal with more complex geometries and/or dynamic load cases. A promising numerical approach is the Discrete Element Method (DEM). Currently, DEM codes are rather specialised research tools, and further development and validation are needed to confirm their suitability. In this paper, the DEM code LMGC90 is used to analyse the responses of arches subjected to dynamic base motions, with the results compared to shaking table experiments on arches built from wooden voussoirs. It is shown that the code is able to model the sequence of hinge openings and the final collapse mechanism extremely well. However, the numerical simulations overestimate the base acceleration amplitudes required to cause collapse. This is thought to be due to the impossibility of modelling the exact experimental set-up, which is substantially affected by small imperfections in the contacts between adjacent voussoirs. The resultant error is found to be quite consistent between tests, and has been compensated by a simple calibration of the experimental models. Future work will seek improved methods of dealing with this issue, and extension of the DEM approach to arches and vaults made of concrete-like materials, with non-zero tensile strength.

PL

Wiele zabytkowych struktur znajdują się w regionach o znacznej aktywności sejsmicznej jest podatnych na uszkodzenia podczas trzęsienia ziemi . Do oceny bezpieczeństwa tych struktur konieczne jest wykonanie kluczowych elementów , takich jak łuki sklepienia. Podczas gdy statyczną stabilność łuków murowych można badać analitycznie wykorzystujący zasady analizy limitu, w bardziej złożonych kształtach i / lub przypadkach stosuje się obliczania dynamicznego obciążenia. Obiecujące podejście numeryczne to Discrete Element Method (DEM) .

3

Effect of fibre reinforcement on the properties of ground granulated blast furnace slag-cement-bentonite slurry

Williams M., Ghataora G. S.

Studia Geotechnica et Mechanica

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2011

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Vol. 33, nr 4

63-83

EN

Slurry walls are used as cut-off walls and are designed to meet strength and permeability criteria, with the latter often being a governing factor. An investigation was undertaken to explore the use of polypropylene fibres in cement bentonite ground granulated blastfurnace slag slurry walls in order to assess the effect of fibres on permeability in the main. Flow, bleed and both undrained and drained strength were also measured. Fibres reduced both the flow and bleed. They also marginally increased the permeability. Undrained strength together with strain to failure increased. However, under drained conditions strain to failure increased compared to mixes with any fibre.