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Scientific Reviewed Papers
Lavasan, Dr.-Ing. A. | Detert, Dr.-Ing. O. | van Duijnen, Dipl-Ing. P.

Numerical simulation of soil nailed retaining systems with geosynthetic reinforcement as the facing support

Abstract

This research numerically examines the stability of a bridge abutment reinforced with grouted nail with geosynthetic facing in service and ultimate load states. Recently, soil-nailing technique has become a widely accepted method to efficiently reinforce the in-situ earth retaining systems. Alt-hough, the face of the retaining systems is very often supported by reinforced concrete elements, recent advancements in geosynthetic reinforcements have shown a potential to use geogrid as the face support for earth retaining structures. However, using different types of reinforcing elements in a single system results in complex soil-reinforcement interactions. With advancements in computational capacities, nu-merical simulation methods have become popular to assess the performance and the stability of geostruc-tures. Despite the popularity of the computational methods for geosynthetic reinforced systems, there is still a debate on appropriate type of elements to simulate reinforcing members and their effects on the numerical predictions. The main difference between the various types of numerical elements (i.e. beam and geogrid elements) is considering the contribution of bending and shear resistances of nails and face support elements to the deformability and stability of retaining system. Several studies indicated that ig-noring the influence of bending and shear resistances result in slight conservatism. However, the influ-ence of such assumptions on the global ultimate stability of the system and safety factor has not received sufficient attention. Therefore, this research aims at evaluation of numerical results for retaining soil structures reinforced by grouted nail and geosynthetic materials under service and ultimate loads for a complex system that consists of pile, grouted nails and geogrid face support.

Conclusion

In present research a bridge abutment system consists of deep battered pile foundation with a nailed slope with flexible geogrid as the facing element is studied. In the numerical analyses, 2 different strategies were adopted that one accounted for the shear and bending resistance of the nails by modeling the nail as beam element. In the second approach, the nail was assumed to behave as an axial element with no bending and shear resistance and the nail was modeled by the use of geogrid element. Additionally, the behavior of the system in terms of the structural forces, mobilization of the shear strength on the domain and the defor-mation of the abutment face was examined at service and ultimate load states. Based on the numerical analyses conducted, the following conclusion can be drawn:
• Geosynthetic reinforcement with sufficient tensile strength and axial stiffness can be successfully used as the facing elements in the nailed slopes. The bending and shear resistance of the nail has a limited influence on the tensile force developed in the flexible geogrid facing.
• Considering the bending and shear resistance of the nails leads to an increase of about 10% in the numerically estimated tensile forces in the nail.
• The horizontal displacement of the abutment face at ultimate load state significantly differs when the nail is modeled as beam element.
• The shear forces at the connection between the piles head and the bank seat increases up to 100% when the nail is simulated as the beam while the distribution of the shear force in the pile length does not change significantly with type of the nail element.