Keywords: reinforced soil walls, codes of practice, numerical analysis, design methods.

This paper presents a case study of reinforced soil retaining walls associated with the construction of the Egnatia Motorway in Greece. The structures studied involve typical wall sections. The global stability analyses take account of the foundation conditions, parameters and ground slope at each of the two worst case sections considered. The paper compares the results of limit equilibrium design methods with the results derived from numerical methods that are based on soil-structure interaction.

The design method used in the calculations is the coherent gravity method as applicable to inextensible reinforcing strips and as described in British Standard BS8006: Strengthened Reinforced Soils and Other Fills [1]. Static designs are initially contemplated in accordance with BS 8006 in order to determine the layout, number and type of strips required at each layer.

There are five main stages in the design process: calculating the tensile forces to be resisted by each layer of reinforcement; considering tension forces in the reinforcements; checking the available bond resistance; considering the long term rupture capacity; checking for the serviceability limit state. The implicit assumptions made in using limit equilibrium methods are that: the soil and all nails reach their limiting state simultaneously (i.e. there is strain compatibility between soil and nails at all stages), and deformations are small enough such that there are no changes in the geometry of the structure prior to failure.

Numerical analyses were performed using the finite difference program FLAC [2] and the finite element program PLAXIS [3] using the reinforcement layout obtained from the limit equilibrium analyses based on BS 8006. The soil mass was modelled as an elastic-Mohr-Coulomb plastic material. The tensile forces developed in the reinforcements, the displacements and the deflection of the face of each wall section have been derived from the numerical analyses. The global stability of each section is also checked for both the static and seismic cases. The global stability checks are confirmed by the observed performance of the walls when analysed using numerical methods.

The tension forces developed in the reinforcement according to the numerical calculations are smaller than the values used in the limit equilibrium analyses. The deflections of both wall sections are smaller than about 3cm. Convergence in the displacement calculations and forces in the reinforcement is observed for both numerical methods of analysis.

1

BS 8006: Code of practice for Strengthened/Reinforced Soils and Other Fills, British Standards Institution, 1995.

2

FLAC (Fast Lagrangian Analysis of Continua), User manual, Itasca Consulting Group, Minneapolis, 1993.

3

PLAXIS, Finite Element Code for Soil and Rock Analysis, 7.2 Professional version, 1998.

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