LARGE SCALE SOIL-STRUCTURE INTERACTION EXPERIMENTS ON SAND UNDER CYCLIC LOADING

摘要

Large-scale specimens of sand were constructed and tested under the cyclic loading imposed on a shallow foundation model, in the framework of the activities of the EC-funded project TR1SEE (3D Site Effects of Soil-Foundation Interaction in Earthquake and Vibration Risk Evaluation). The tests were designed to provide validation data for the calibration of new and existing constitutive soil models, and to improve the assessment of the permanent deformations and bearing capacity of the soil-foundation systems. Two tests were performed, with relative densities 45% and 85%. The set-up consisted of a model of shallow foundation (1m x 1m in plan) resting on a large volume (4.6m x 4.6m, 3 m deep) of saturated sand of uniform properties, and well known geo-mechanical characteristics (Ticino sand). The specimens were subjected to the same loading sequence. After application of the vertical load and stabilization of the settlement, a series of small-amplitude force cycles of increasing level were applied, to identify the onset of non-linear behaviour. A realistic time-history of horizontal force and overturning moment, representative of the seismic actions transmitted by the super-structure to the foundation during an earthquake was then applied on top of the foundation. This resulted in non-linear behaviour, with development of significant permanent settlements and rotations. Finally, a series of displacement cycles of increasing amplitude were applied, up to the ultimate capacity of the soil-foundation system. The paper provides a description of the experimental activity and of the global results. In particular, the different behaviour of the high and low-density specimens is discussed. The limitations of the set-up are critically analized. Some relevant engineering results, especially the permanent deformations developed during the earthquake-like loading phase, are illustrated and emphasis is given to the need for improving the current predictions of earthquake-induced foundation settlements and rocking.