Zur Bemessung der Verankerung von Bewehrungsgittern aus Kunststoff beim Schutz von Böschungen vor hangparallelem Gleiten

On the design for the anchorage of geogrids used to prevent sliding failure on slopes.

Geogrids, which are installed to prevent sliding failure on long and steep slopes, have to be anchored safely. The design and calculation of the anchorage is based on simple design rules. Basically it is assumed that the pull-out strength is proportional to the soil shear strength, the vertical load and the anchoring length and that the soil-reinforcement coefficient of proportionality as determined in pull-out tests is typically in the range between 0.5 and 1. Based on models for the soil-geogrid interaction the physical assumptions and limitation of these rules are discussed. It is shown that they are only applicable without restrictions for geogrids, the pull-out resistance of which are essentially due to surface friction between soil particles and the surface of the longitudinal tensile force carrying grid elements (so called friction geogrids). In this case the soil-reinforcement coefficient as determined from the pure surface friction between soil and longitudinal elements has to be used for a safe calculation of the pull-out strength. Geogrids, for which the passive thrust mobilization of earth pressure by the displacement of the transversal or bearing force grid elements substantially contributes to the pull out resistance (so called earth pressure geogrids), the mechanical strength of the junction between longitudinal and transversal elements is of crucial importance. The relation between mechanical properties of the junction, the flexibility of the longitudinal grid elements, the surface friction and the finally achieved pull-out resistance is exemplary shown by model calculations. There is a certain upper limit of the strength of the junction embedded into the soil and for a safe design it is not allowed to go beyond that limit. This requirement restricts the range of application of the common design rules. There are two cases. For soils with low enough shear strength the mobilized earth resistance may be well below the limit of the confined junction strength and the rules may be applied. In all other cases the rules have to be substantially modified. The mechanical strength of the confined junction corresponds to an upper limit to the anchoring length which can actually be mobilized. Then, only tensile forces below a critical value can be safely anchored completely independent from the actual design value of the tensile strength of the tensile force bearing longitudinal grid elements. These limi tations have to be observed to achieve a safe design of the anchoring.