Principle Investigation and Description of the Stress-Strain Behaviour of the Composite Material "Geogrid Reinforced Soil"
Final Report Abstract
Interaction experiments with transparent soil were performed to investigate the load transfer at different geosynthetic-soil interfaces. A new experimental setup was presented to provide precise details and a more realistic insight by representing different modes of interaction within the interaction experiments. The transparent soil technique was used to record the geosynthetic-soil interaction unobstructed and continuously by digital image analysis. The transparent soils FQfine and FQcoarse were proved to be feasible surrogates to mimic the behaviour of natural sand and gravel based on comparable stress-strain and compression response. The results of this research are important to understand the mobilisation of indirectly activated geosynthetic reinforcements by the adjacent fill, which is the predominant in most applications such as base layers of dams and embankments, foundation pads and reinforced soil walls, to name but a few. The modes of interaction were discussed based on relative displacements between geosynthetic and soil, deflection of geogrid transverse members, mobilised tensile load and interfacial shear stress. For indirectly activated geosynthetic reinforcements three distinct modes of interaction were identified: force transfer from soil to geosynthetic (pushout), anchoring of geosynthetic tensile load to fill (pullout) and zone of equilibrium (interlocking). Thus, the proposed micro-mechanical conceptual model for indirectly activated geogrids was validated. The mechanisms and proportions of load transfer were determined based on modified reinforcement by removing specific transverse members. The total load transfer is composed of two mechanisms: the friction on the geosynthetic surface and the bearing of the transverse members. The contribution of friction to the total load transfer decreases with increasing relative deformation between geosynthetic and adjacent soil. The transverse ribs were progressively activated as the relative displacements increased. Furthermore, the effects of geogrid aperture size, tensile stiffness, geogrid type and reinforcement configurations, properties of the fill, confining stress and load plate configurations on the development of interaction zones and interface performance were investigated. The interfacial shear stresses were reduced as the ratio of geogrid aperture to mean particle size increased, resulting in lower geogrid loads. Higher geogrids loads were mobilised with increasing tensile stiffness of the reinforcement, but lower displacements of geogrid and adjacent soil occurred. Consistent results and similar reinforcement performance were found for woven PET and laid PP geogrids. The largest load transfer was found for the aperture configuration with a pair of two closely spaced transverse members at each position. In contrast, for a geocomposite consisting of a geogrid attached to a non-woven geotextile, a reduced reinforcement performance was found due to the reduced contribution of the particle-aperture interaction. In the fill with lower shear strength, the geosynthetic contributed with higher tensile load to establish equilibrium and larger deformation were observed. The increase in tensile load was found in the same order of magnitude as the decrease in internal shear strength of the fill. In load plate tests, the formation of the three interaction zones pushout, pullout and interlocking confirmed the conceptual model for the loading scenario representing a reinforced footing. The pushout mechanisms at the edges of the load plate indirectly mobilised the reinforcement. For load arrangements where the reinforcement length was shorter than the required anchoring length, the pullout length was too short to fully anchor the geosynthetic tensile load and the interlocking zone was not formed. As the confining stress increased, lower geosynthetic and soil movements were observed resulting in lower interfacial shear stresses and tensile loads along the reinforcement. Based on the experimental results, the stress-dependent relationship between interfacial shear stiffness and relative movement was derived. It was found that the initial shear stiffness of the interface increases with increasing confining stress. However, the shear resistance of the interface degraded with increasing relative movement between soil and geogrid. This relationship is considered as an important input parameter for numerical modelling approaches and can be determined for geosynthetic-soil interfaces with direct shear tests.
Publications
- (2019). Interaction behaviour of geogrids in transparent soil. Proceedings of the 17th African Regional Conference on Soil Mechanics and Geotechnical Engineering, Cape Town, South Africa, 267-272
Derksen, J., Ziegler, M.
- (2019). Untersuchungen zum Interaktionsverhalten von Geogittern im transparenten Boden. 16. Informations- und Vortragstagung über Kunststoffe in der Geotechnik - FS-KGEO 2019, Würzburg, Deutschland, 536-541
Derksen, J., Ziegler, M.
- (2020). Investigations on indirect geogrid activation in transparent soil. Proceedings of the 4th Pan American Conference on Geosynthetics, Rio de Janeiro, Brazil
Derksen, J., Ziegler, M.
- (2021). Geogrid-soil interaction: A new conceptual model and testing apparatus. Geotextiles and Geomembranes, Elsevier, 1393-1406
Derksen, J., Ziegler, M., Fuentes, R
(See online at https://doi.org/10.1016/j.geotexmem.2021.05.011) - (2021). Mikro- und makroskopisches Interaktionsverhalten von geogitterbewehrten Konstruktionen. 17. Informations- und Vortragstagung über Kunststoffe in der Geotechnik - FS-KGEO 2021
Derksen, J.
- (2022). Geogrid-soil interaction: Experimental analysis of factors influencing load transfer. Geosynthetics International, ICE Publishing
Derksen, J., Fuentes, R., Ziegler, M.
(See online at https://doi.org/10.1680/jgein.21.00110)
