Abstract
The cyclic simple shear tests can be used to reproduce in laboratory the complex behaviour of the soil during an earthquake, simulating the continuous rotation of the principal stress axes. In this research a comparison of results between cyclic simple shear tests carried out with confining pressure or confining rings is reported. A cyclic simple shear apparatus is used to carry out tests with confining rings (the conventional way to carry out cyclic simple shear tests) and with a confining pressure applied to the specimen through pressurized water, where the K0 condition during consolidation is guaranteed by a sophisticated control system. The apparatus, in both the configurations, is described in detail. All tests were carried out on reconstituted specimens of an Italian sand with similar initial conditions, such as low relative density and confining pressure. All experimental results are reported in the plane cyclic stress ratio (CSR) and number of cycles where liquefaction occurs (Nliq) in order to evaluate the effect of confinement on the liquefaction resistance of the studied sand.
Highlights
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At the University of Napoli (Federico II) a new cyclic simple shear equipment has been used. In this apparatus two different configurations are possible: the first one is a configuration with confining pressure, the second one is that with confining rings
In undrained conditions, the volume is constant and to keep the constant diameter, the height of the specimen is maintained constant, it is achieved by allowing changes in the total vertical stress during this phase
Summary
As already mentioned cyclic simple shear tests can simulate stress conditions in situ during an earthquake, allowing the continuous rotation of principle stress axes. In undrained conditions (constant volume) the height of the specimen is constant and the cell pressure changes to maintain the total vertical stress constant. In undrained conditions, the volume is constant and to keep the constant diameter, the height of the specimen is maintained constant, it is achieved by allowing changes in the total vertical stress during this phase. In both the configurations, a pore pressure transducer is used to measure the pore pressure during cyclic phase and a horizontal and a vertical LDT are used to measure the axial and shear strains. The configuration with flexible boundary can be advantageous compared to rigid one because the stress state of the specimen is known, while with rings the lateral stress is unknown, because there is not a cell pressure
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