Abstract
As well known, rockfill behaviour is strongly influenced by both intrinsic (mineralogy and size of particles, grain shapes, soil grading etc.) and state parameters (relative density, stress state, relative humidity). To investigate their mechanical response to stresses and relative humidity (RH) loadings, a large size triaxial device (H = 410 mm, D = 200 mm) has been developed at the University of Naples Federico II (Italy), including modifications required to impose partially saturated conditions in the specimen by means of the vapour equilibrium technique. In order to evaluate local axial and radial strains and global volumetric strains in partially saturated conditions, a magnetic shape detector device has been designed and installed. The accuracy of this system has been evaluated in some isotropic compression triaxial tests on compacted sandy-gravel specimens. The experimental data clearly show the effectiveness of the magnetic system in the measurement of axial displacements while the measurement in radial direction appear to be strongly affected by the non-linearity of the complex magnetic field generated during the test and requires further checking tests.
Highlights
IntroductionThe mechanical characterization of coarse-grained soils has been traditionally performed by laboratory tests in large oedometer and/or triaxial devices
The mechanical characterization of coarse-grained soils has been traditionally performed by laboratory tests in large oedometer and/or triaxial devices.Over the years, testing equipment underwent significant changes to enable a reliable description of their stress-strain behaviour in partially saturated conditions [1]
A novel feature of the High Pressure Stress Path (HPSP) cell is the use of a magnetic system called Magnetic Shape Detector (MSD)
Summary
The mechanical characterization of coarse-grained soils has been traditionally performed by laboratory tests in large oedometer and/or triaxial devices. Transmitting the feedback signal for cell and pore pressure control; a differential pressure transducer (DPT) to measure the volume changes of the specimen by the volume of water exchanged along the drainage line (tests on water saturated specimen) or by the volume of water exchanged by the cell (tests on unsaturated specimens); the LVDT for measurement of axial strains; an LVDT for measurement of the displacements of the pressure multiplier (external Volume Gauge). A novel feature of the HPSP cell is the use of a magnetic system called Magnetic Shape Detector (MSD) This system was designed for the measurement of local axial and radial strains as well as for the measurement of global volume strains in partially saturated conditions. Having noted the positions of the bases and the lateral profile, the current volume of the specimen is measured by an integral calculation
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