The results of an experimental study on the mechanical behaviour of the natural soft clay found at Pisa are discussed. Triaxial and true triaxial stress path—controlled tests were carried out, in which the soil was subjected to a variety of drained stress paths, each starting from the in situ stresses. The stress—strain behaviour was observed to be substantially non—linear from the very beginning of the loading process. The observed results are interpreted using concepts of hardening plasticity. The influence of the damage produced in the clay microstructure during loading is evaluated through a normalization technique. A comparison between the behaviour of the natural and the reconstituted clay is also presented. The results of the true triaxial tests show strength anisotropy. In both the triaxial and the true triaxial tests, the observed stiffness was found to depend strongly on the direction of the stress path. Dans cet exposé, nous présentons les résultats d'une étude expérimentale sur le comportement mécanique de ľargile tendre naturelle trouvée dans la région de Pise. Nous avons effectué des essais de contrainte triaxiale et de contrainte triaxiale réelle á trajectoire conrô1ée, essais au cours desquels le sol a été soumis á une variété de trajectoires de contrainte drainées, chacune commençant á partir des contraintes in situ. Nous avons observé que le comportement contrainte—déformation était substantiellement non linéaire depuis le commencement du processus de charge. Nous appliquons des concepts de plasticité durcissante pour interpréter les résultats observés. Nous évaluons ľinfluence des dé gâts infligés â la microstructure de ľargile pendant la charge grâce á une technique de normalisation. Nous comparons aussi le comportement de ľargile naturelle et de ľargile reconstituée. Les résultats des essais triaxiaux réels ont mis en évidence une anisotropie de résistance. Dans les essais triaxiaux tout comme dans les essais triaxiaux réels, il est apparu que la rigidité observée dépendait fortement de la direction de la trajectoire de la contrainte.

In recent years, the designers of long girder bridges in seismic areas have frequently opted for a continuous deck. One implication of this choice is that in many instances bridge abutments are called upon to carry large seismic forces, engaging the dynamic response of the soil–abutment system. To deal with this problem, this paper describes the formulation of a novel one-dimensional, inertial macroelement for simulating the dynamic behaviour of bridge abutments. The non-linear force–displacement relationship is characterised by a multi-surface plasticity model using a rigorous thermodynamic approach. The plastic response of the model is bounded by the ultimate capacity of the soil–abutment system that includes dissymmetry of the soil response in active and passive loading directions, while inertial effects transferred by the near-field approach embankment are simulated through appropriate participating masses in the macroelement formulation. The paper describes a straightforward calibration procedure of the proposed macroelement for horizontal, longitudinal loading of the abutment. The macroelement has been incorporated into a simplified, global, finite-element model of a multi-span girder bridge and validated through comparisons with results from a full three-dimensional (3D) dynamic time domain analysis under seismic loading. The inertial macroelement predictions of abutment deformations, axial deck loads and pier reaction forces are in very good agreement with the 3D soil–structure interaction model, and are achieved at much lower computational costs. The proposed inertial macroelement represents a significant improvement over existing simplified models based on linear response of the soil–abutment system.

In this paper, the seismic behavior of embedded cantilevered retaining walls in a coarse-grained soil is studied with a number of numerical analyses, using a nonlinear hysteretic model coupled with a Mohr-Coulomb failure criterion. Two different seismic inputs are used, consisting of acceleration time histories recorded at rock outcrops in Italy. The numerical analyses are aimed to investigate the dynamic behavior of this class of retaining walls, and to interpret this behavior with a pseudostatic approach, in order to provide guidance for design. The role of the wall stiffness on the dynamic response of the system is investigated first. Then, the seismic performance of the retaining walls under severe seismic loading is investigated, exploring the possibility of designing the system in such a way that during the earthquake the strengths of both the soil and the retaining walls are mobilized. In this way, an economic design criterion may be developed, that relies on the ductility of the system, as it is customary in the seismic design of structures