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%0 Thesis
%A Jacobs, Felix
%T Interaktionsmodell zur Bemessung von Verankerungsgräben mit Geogittern
%I Rheinisch-Westfälische Technische Hochschule Aachen
%V Dissertation
%C Aachen
%M RWTH-2016-11974
%P 1 Online-Ressource (XXIV, 212 Seiten) : Illustrationen, Diagramme
%D 2016
%Z Veröffentlicht auf dem Publikationsserver der RWTH Aachen University 2017
%Z Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2016
%X Since the 1970’s geogrids are being used for soil reinforcement in all fields of geotechnics as in bearing layers under transportation ways and foundations and as in slopes. Generally, it is the goal to build these bearing layers stiffer and these slopes steeper than possible with a locally available soil without additives. The reinforcement of locally available soils additionally leads to more economic and sustainable constructions.Surface-parallel geogrids in slopes, as in veneer cover systems, e.g., of landfills, take up the downward-directed part of the top soil’s weight. Hence, the geogrid tensile force increases along the slope from bottom to top. This high tensile force has to be anchored within a small area at the top, which is often carried out in anchorage trenches. The current design of the German EBGEO (2010) regards only the ultimate and not the serviceability limit state, and is based on some assumptions that, based on this work and e.g. BAM (2012), are rated to be too simplifying. Additionally, the design does not comprise a proof of the junctions between longitudinal and transverse tensile members of the grids, although these are being loaded regularly. Especially in regard to landfill constructions with their required endurance of 100 years, a design model should be sufficiently detailed and conservative (Koerner 2012a, p. 454). Due to these arguments, the execution of anchorage trenches in landfill constructions in Germany is currently restricted. Therefore, in this work a mechanically based model for the design of anchorage trenches with geogrids, taking into account all decisive effects, was developed to resolve the uncertainties of the current design after EBGEO (2010). After a comprehensive literature review, the nonlinear influences on the pullout behavior of normal stress, number of transverse members, soil type and soil density were quantified with pullout tests using four geogrid products and three soils. Basing on these findings, a mechanically based interaction model for horizontal anchorage was developed that combines various existing approaches and takes into account the load transfer mechanisms of friction on the surfaces of the longitudinal tensile members as well as bearing in front of the transverse tensile members.For use in an anchorage trench with a non-horizontal but deviated geogrid alignment, this model had to be upgraded. Therefore, approaches to take into account deviation effects and different possible failure mechanisms were combined with the interaction model for horizontal anchorage. With its mechanically based approaches for the interaction, the deviation effects and the failure mechanisms and due to its successful validation, this model could be used for modeling the resistance mobilization of geogrids in anchorage trenches.With the developed anchorage trench model, the design approach of EBGEO (2010) was checked with characteristic calculations within a parametric study. The comparison showed that the deviations along the geogrid led to an increase in resistance and in stiffness of anchorage trenches. In almost all cases, the failure mechanism sliding with only resistance forces at the bottom side of the geogrid was decisive, which is not considered in the current design practice. In total, the design of EBGEO (2010), even when considering the mechanism sliding, tended to unsafe results for anchorage trenches with lower stiffness. In order to still be able to safely design with the approach of EBGEO (2010), the resulting resistance has to be reduced by a model factor of γMF,EBGEO = 1.67. Only for anchorage trenches with higher stiffness of kR ≥ 1820 kPa, EBGEO design leads to safe results without the model factor. However, in almost all cases, design with EBGEO (2010) and the model factor is not economic.For safe and, at the same time, economic design of geogrid anchorage trenches, the model was incorporated into a design concept, which was based on the existing design concept for anchorage trenches. For the known proofs of the ultimate limit state, the model gives the design resistance, while the tensile force resulting at the top of the slope, as design action, can still be determined according to EBGEO (2010). Additionally, the design model comprises two proofs against failure of the junctions between longitudinal and transverse tensile members (shear resistance and maximum allowable displacement), for which the model calculates the design actions. For the first time, with the developed model a design of the serviceability limit state is possible. For these, the model calculates the geogrid displacement at the top of the slope for the regarded load case as design action.To be able to use the design model for design of the ultimate limit state not only with the written code and the software Matlab, but also with a simple spreadsheet calculation, it was simplified by a coarse discretization of the geogrid into only three sections. The resulting reduced accuracy of the simplified design model is taken into account using a stiffness-dependent model factor that was defined.Thereby, a safe design of the ultimate limit state is possible with the simplified design model as well as the detailed design model, in contrast to design with EBGEO (2010), including a proof of the geogrid junctions. By introduction of a model factor for the approach of EBGEO (2010), design using EBGEO (2010) is still possible. However, this design is less economic than using the presented new design models. Additionally, with the detailed design model, for the first time, a design of the serviceability limit state is possible.
%F PUB:(DE-HGF)11
%9 Dissertation / PhD Thesis
%U https://publications.rwth-aachen.de/record/680774