Discrete element simulation of geogrid-stabilised soil     

Michael Stahl  Heinz Konietzky  Lothar te Kamp  Hein Jas 《Acta Geotechnica》2014,9(6):1073-1084

A particle-based numerical simulation procedure is presented for the generation and calibration of geogrid-stabilised soil on the basis of experimental data. The paper describes how to simulate a biaxial geogrid depending on a specific particle and parallel bond model. Numerical and experimental pull-out tests have been performed to reproduce the pull-out force–strain behaviour of a biaxial geogrid specimen embedded in granular material under special consideration of the grain-size distribution, initial relative density, normal stress state as well as sample installation. Model analysis of soil mobilisation and geogrid deformation is presented to understand the significance of the interlocking effect as key mechanism for soil stabilisation. The procedure can be used for further investigations of the influence and effects of soil stabilisation depending on the significant properties of the interacting components (soils and geogrids).  相似文献   

New coelacanth material from the Middle Triassic of eastern Switzerland, and comments on the taxic diversity of actinistans     

Lionel Cavin  Heinz Furrer  Christian Obrist 《Swiss Journal of Geoscience》2013,106(2):161-177

New coelacanth material from the Middle Triassic Prosanto Formation of the Ducan and Landwasser area near Davos in eastern Switzerland, Canton Graubünden, is described. A sub-complete individual is visible in ventral view, and shows details of its branchial apparatus. In particular, it possesses relatively large teeth on the ceratobranchials, and possible ossified hypobranchials. Few diagnostic characters are observable, and most of them are visible on the mandibles preserved in lateral view. This specimen shares characters with Ticinepomis peyeri, a smaller form from the Middle Triassic of Monte San Giorgio, whose holotype is re-described in part here. A second specimen, a fragmentary caudal skeleton shows the typical supplementary lobe of coelacanths, and meristic characters indicating probable close affinities with T. peyeri. We refer this material to Ticinepomis cf. T. peyeri. Because the new specimen is larger than the holotype, we refute the possible juvenile status of the small specimen from Monte San Giorgio. The new material of Ticinepomis from Canton Graubünden shows anatomical features not preserved on the holotype and allows the addition of new characters to a previously published data matrix of actinistians. A phylogenetic analysis is performed, which supports that Ticinepomis is nested among the Latimeriidae. The diversity of post-Palaeozoic coelacanths is assessed. The taxic diversity of observed occurrences shows a peak in the Early Triassic and a peak in the Late Jurassic, as detected in previous studies. When ghost lineages are included in the computation, the Late Jurassic peak is smoothened. By comparing the taxic diversity curves with the curve of average ghost lineage duration, we conclude that the Early Triassic peak of diversity was probably caused by a biological radiation, whereas the Late Jurassic peak of observed diversity is probably the result of a Lagerstätten effect.  相似文献   

Little-known brachiopods from the Cretaceous of the Helvetic realm of NE Switzerland (Alpstein) and W Austria (Vorarlberg)     

Heinz Sulser  Georg Friebe  Peter Kürsteiner 《Swiss Journal of Geoscience》2013,106(2):397-408

Three species from different stratigraphical levels of the Cretaceous of the Helvetic Alps are described. (1) Rhynchonellid specimens from the upper Öhrli-Kalk (Öhrli Formation, Late Berriasian) of NE Switzerland (Alpstein) identified as Lamellaerhynchia heimi (Sulser 2008) [Rhynchonellida, Hemithiridoidea]. Its range appears to be limited to a small area of the carbonate platform of the northern Alpstein chain. Based on internal and external morphological criteria L. heimi differs from other species of Lamellaerhynchia, as well as from Burrirhynchia cf. sayni (Jacob & Fallot 1913), occurring in the younger carbonate platform of the Schrattenkalk Formation (Early Aptian). (2) Recently collected material in various localities of the Altmann Member (Tierwis Formation, Late Hauterivian to Early Barremian) in the Alpstein area identified as Oblongarcula cf. alemannica Owen 1977 [Terebratellidina, Laqueoidea]. This species is closely related or identical to O. alemannica of the North European Boreal province and gives a reference to the occurrence of the genus Oblongarcula in the Tethyan domain of the Alps. Partially silicified specimens enable in rare cases a direct access to internal structures after that they were exposed by an acid treatment. (3) Tulipina koutaisensis (Loriol 1896) [Terebratellidina, Kingenoidea], known from Aptian deposits in the central Caucasus of Georgia, has been recorded as a rare species in the Plattenwald-Bed (Selun Member of the Garschella Formation, Albian) of W Austria (Vorarlberg). The localised occurrence and the temporal gap between the Caucasian and the Helvetic T. koutaisensis suggest an east–west directed migration along the northern margin of the Tethys Ocean during the Early Cretaceous.  相似文献   

Modification of climate signals by human activities recorded in varved sediments (AD 1608–1942) of Lake Holzmaar (Germany)     

Ulrike Kienel  Heinz Vos  Peter Dulski  Andreas Lücke  Robert Moschen  Norbert R. Nowaczyk  Markus J. Schwab 《Journal of Paleolimnology》2013,50(4):561-575

Paleolimnological data from varved sediments in Lake Holzmaar (Eifel, Germany) were combined with documentary data on human activities, long-term data from the Historical Climate Database (HISKLID) for Germany and with recent monitoring data to evaluate changes in deposition that arose from climatic and human influences. The sediment data included seasonal layer thickness in an established varve chronology (1608–1942 AD), subannual chemical element counts, and multiannual organic matter data (TOC, TN, δ¹³C_org), all combined on an annual scale. Indicators for detritus deposition (lithogenic element counts and detritus layers) determined the first principal component (PC1) of the sediment data. This detritus PC1 was compared to the first PCs of the seasonal precipitation and temperature from HISKLID. While no relation was found to precipitation, the correlation with the temperature PC1 determined by spring to fall temperatures was significant. From 1608 to 1870, a positive correlation of the PCs suggests an increase of detritus deposition in the lake center with increasing non-winter temperatures. These may be linked by lake-internal sediment redeposition that increases when the periods of winter stratification become shorter and that of lake circulation longer. The detritus deposition is modulated by external detritus input depending on the intensity of erosion-conducive land use (wood pasture, wood cutting, and rotational slash-and-burn cultivation). Detritus input diminished when land use slowed down with population decrease as the consequence of plague epidemics, warfare and emigration. After 1870, forest regeneration and improving agricultural practices led to a stabilization of the catchment. Erosion and detritus deposition decreased progressively. The negative correlation of detritus deposition with the gradually increasing temperature presumably mimics a cause-effect relation, although a link with decreasing freeze–thaw action is possible. The modernization of agriculture proceeded with manuring and fertilizing, which caused an increase of lake productivity as indicated by summer blooms of diatoms with enhanced nutrient demand, increased δ¹³C_org values and sulfur concentrations. Within this well established data base we found combinations of criteria that may be used to deduce natural climatic or anthropogenic influences. The quantitative attribution of these influences remains a challenging task in paleolimnology because their interaction makes the detection of linking mechanisms difficult even at high degree of detail and the processes themselves remain debatable.  相似文献   

A Comparative Study of Different Approaches for Factor of Safety Calculations by Shear Strength Reduction Technique for Non-linear Hoek–Brown Failure Criterion     

Sukanya Chakraborti  Heinz Konietzky  Katrin Walter 《Geotechnical and Geological Engineering》2012,30(4):925-934

The shear strength reduction technique is becoming more and more popular to determine the factor-of-safety for geotechnical constructions, especially for slopes. At present, two in principal different procedures are used to apply the numerical shear strength reduction technique for materials characterised by non-linear failure envelopes, like the Hoek–Brown criterion. One procedure is based on the determination on local stress and strength values, whereas the other is based on a global linearization of the non-linear failure envelope. This article shortly describes and discusses these two different procedures and compares results for a broad spectrum of parameter constellations based on slope stability calculations. The local approach is physically more correct. The global approach can be considered as a first approximation. A comparison of both methods reveal that the global approach in comparison to the local approach, can leads to a deviation of up to 15?% in both directions. If one considers the local approach as the ‘correct’ one, depending on the parameters the results of the global approach can lie on the safe or unsafe site. The practical conclusion is that evaluation of slope stability using the global approach can result in uneconomic slope design or overestimation of safety margin. The use of the local approach instead of the global should be preferred. In case of small safety margins (e.g. 20?% or less) the use of the local approach is strictly recommended.  相似文献   

Late glacial environment and climate development in northeastern China derived from geochemical and isotopic investigations of the varved sediment record from Lake Sihailongwan (Jilin Province)     

Jörn Parplies  Andreas Lücke  Heinz Vos  Jens Mingram  Martina Stebich  Ulrich Radtke  Jingtai Han  Gerhard H. Schleser 《Journal of Paleolimnology》2008,40(1):471-487

Total organic carbon (TOC) content, total nitrogen (TN) content, stable nitrogen isotope (δ¹⁵N) and stable organic carbon isotope (δ¹³C_org) ratios were continuously analysed on a high resolution sediment profile from Lake Sihailongwan (SHL), covering the time span between 16,500 and 9,500 years BP. Strong variations of the investigated proxy parameters are attributed to great climatic fluctuations during the investigated time period. Variations in organic carbon isotope ratios and the ratio of TOC/TN (C/N ratio) are discussed with respect to changing proportions of different organic matter (OM) sources to bulk sedimentary OM. Phases of high TOC content, high TN content, depleted δ¹³C_org values and high δ¹⁵N values are interpreted as times with increased productivity of lacustrine algae in relation to input of terrigenous organic matter. Two distinct phases of enriched nitrogen isotope ratios from 14,200 to 13,700 and 11,550 to 11,050 years BP point towards a reduced phytoplankton discrimination against ¹⁵N due to a diminished dissolved inorganic nitrogen pool. The combination of geochemical (TOC, TN, C/N ratio) and isotopic (δ¹³C_org, δ¹⁵N) proxy parameters points to a division of climate development into four stages. A cold and dry stage before 14,200 years BP, a warm optimum stage with high phytoplankton productivity from 14,200 to 12,450 BP, a colder and drier stage from 12,450 to 11,600 BP and a stage of climatic amelioration with high variability in TOC and TN contents after 11,600 BP. These results are discussed in relation to monsoon variability and Northern Hemisphere climate development of the late glacial.  相似文献   

Community strategies to promote sustainable wetland-based food security in rural areas of Zimbabwe     

Thomas Marambanyika  Heinz Beckedahl  Njoya Silas Ngetar 《GeoJournal》2017,82(5):987-1003

This article explores the various strategies rural households employ to sustain wetland use and conservation in the context of the restrictions imposed by the existing legal framework in Zimbabwe. Wetland cultivation is a common feature of the rural landscape and is mainly triggered by subsistence households endeavouring to stabilize their food security, especially in semi-arid and arid environments of the developing countries. Data was collected through a household questionnaire survey, key informant interviews, document review and direct observations. Quantitative data was analysed using ANOVA, Spearman Correlation Coefficient and Wilcoxon in Statistical Package for Social Scientists, whereas qualitative data was subjected to thematic analysis. The results revealed that most households adjacent to wetlands were food secure as wetland conditions enable the provision of a wide range of crops and natural products, contributing almost half of the food directly consumed and 48.2 % of average annual household total cash income. It was also observed that various soil and water conservation practices were adopted and local institutional arrangements were put in place to oversee their effective implementation. Thus, the general result has been increased wetland productivity, improved livelihoods and ecosystem protection. This has largely rendered the impact of legislation restricting wetland cultivation subtle in the local context. The study concluded that there is a need to promote participatory wetland management based on low-cost approaches sensitive to local conditions and the needs and practices of the local communities.  相似文献   

Neubenennungen lithostratigraphischer Einheiten in der Helvetischen Kreide     

Schweizerisches Komitee für Stratigraphie  Thierry Adatte  Jean-Pierre Berger  Hansruedi Bläsi  Reto Burkhalter  Stephan DallAgnolo  Danielle Decrouez  Hanspeter Funk  Heinz Furrer  Yves Gouffon  Hansruedi Graf  Werner Heckendorn  Wilfried Winkler 《Swiss Journal of Geoscience》2009,102(2):363-364

In September 2007 Föllmi and coauthors requested the approval of four lithostratigraphic terms of the Swiss Committee of Stratigraphy (SCS). These terms were to be used in their publication on the Cretaceous in the Helvetic realm (Föllmi et al. 2007). At its meeting on October 18, 2007, the SCS decided the following: The Tierwis Formation (replacing the Drusberg Formation) was accepted, with the reserve that a section at Tierwis should be published in the near future. For the former “Lower Orbitolina Beds” the term Rawil Member was accepted, but here too a better type section than the one at Rawil Pass should be published. The term Rohrbachstein bed should not be used as a formal unit because it describes only a minor lithologic variation within the Grünten Member. The term Plaine Morte bed for a thin condensed horizon can not be accepted due to the fact that its definition is based mainly on biostratigraphy. Furthermore, the duplication a locality term which is in use for a previously established lithostratigraphic unit should be avoided.  相似文献   

Association Announcement, 1997 ANDREI BORISOVITCH VISTELIUS RESEARCH AWARD     

Heinz H. Burger 《Mathematical Geology》1999,31(3):351-353

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T. R. MCDONOUGH: Space. The Next Twenty-Five Years. John Wiley & Sons,Inc., New York,Chichester, 1987, 237 Seiten,Preis: 14.25 ISBN 0-471-85671-1     

Heinz Tiersch 《Astronomische Nachrichten》1988,309(4):262-262

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