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Advances and uncertainties in the design of anchored retaining walls using numerical modelling

The paper describes a research on the prediction of horizontal displacements and internal forces in an anchored wall for the protection of an excavation, by the use of standard field and laboratory tests and a finite element programme with such a soil model which can simulate the essential aspects of soil behaviour at the construction site. It is important to be acquainted with the constitutive model incorporated in the programme, and the selection of appropriate soil parameters for the numerical analysis is the crucial part of modelling. It is, thus, useful to carry out numerical simulations of standard laboratory tests with the well-known soil behaviour in order to select relevant parameters for the simulation of the actual construction process. It is shown in the paper that the measurements of shear wave velocities, which can provide the soil stiffness at very small strains, can be useful also for the determination of the static stiffness at the magnitude of strains relevant for the geotechnical structure under consideration, both for cohesive and noncohesive soils. The research was carried out by a detailed analysis of a case history involving an anchored reinforced concrete wall supporting the walls of an excavation in a relatively stiff soil. The wall displacements were monitored by an installed inclinometer. The major part of the paper is devoted to the analysis of the selection of parameters, especially stiffness parameters. The simulation of triaxial consolidated undrained tests was used in order to assess the reduction of the secant stiffness modulus with the increase of relative mobilized shear strength for the hard clay layer according to published empirical evidence. It is shown that by the selection of appropriate stiffness parameters for the soil model used in the numerical analysis, it is possible to get an acceptable prediction of the anchored wall displacements. This is just one example of a successful analysis but it is encouraging in the way that it shows how it is possible to make reliable predictions based on standard field and laboratory tests and with the use of an available computer programme with a realistic soil model.

anchored wall; soil model; shear stiffness; numerical modelling; measured displacements

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