Experimental data about cyclic stress-strain behaviour under torsional loading of structurally complex formation cropping out in central Italy
This data article presents the results obtained by means of combined resonant column and torsional shear dynamic tests (RCTS), using a Wykeham Farrance device performed at the Geotechnical Laboratory of the University of Bari Aldo Moro on 10 undisturbed isotropically consolidated fine-grained speciments taken from 10 sites in Central Italy. Two types of data are provided in the present paper. The first one contains the analyzed data of samples size and index properties of soils. The second one contains dynamic properties such as resonant frequency and viscous damping ratio measured from RC tests and 199 records concerning the variation of G/G0 (shear modulus ratio) and D (damping ratio %) in function of angular strain ɣ (%) with the number of cycles measured from CTS tests. Stress-strain degradation response curves of each samples are provided and descriptive pictures of specimens are given.
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Combined resonant column and torsional shear dynamic testing device (RCTS) was used for the automatic determination of the damping ratio and shear modulus of 10 soil samples belonging to structurally complex formations cropping out in central Italian Apennines. Measurements of data and analysis were performed according to the ASTM D 4015-15. The device combines the features of both resonant column and torsional shear into a single unit including the current driven motor to apply torsional loads to the samples, a vertical displacement transducer, a cell, back and pore pressure electro-pneumatic systems, a proximity transducers and data logger. The soil resonant frequency was measured by Resonant Column test; a cylindrical soil specimen is restrained at the bottom and dynamically excited at the top. The torsional force at the top is generated using an electrical motor constituted by eight drive coils encircling four magnets attached to a drive plate. The generated frequency is up to 250 Hz and the fundamental mode of vibration is found from the maximum amplitude of motion. The corresponding shear strain is evaluated from the motion amplitude. Viscous damping of materials was determined by free-vibration decay curve, which is generated by shutting off the driving power. The shear modulus and hysteretic damping ratio were evaluated by the Torsional Shear Test; a cylindrical soil specimen is deformed cyclically at a low frequency (a maximum of 10 Hz), continuously monitoring torsion deformations. Subsequently the relationship between torque stresses and torsional shear strain was obtained, which in turn provided the shear modulus and hysteretic damping ratio curves.