333 research outputs found
Microstructural Changes in Clays Generated by Compression Explored by Means of SEM and Image Processing
No full textAbstractA study on the microstructure of an illitic marine clay is carried out through a thorough investigation of the clay origin, composition and current microstructure. The clay fabric is investigated by means of scanning electron microscopy (SEM) and statistically analysed by means of image processing. The nature and strength of the clay bonding are probed by means of direct chemical micro-analyses and on purpose strain paths. The same investigation is carried out both on the natural and on the reconstituted clay, at the initial state and after one-dimensional compression to medium and large pressures
Mechanics of a tectonized soil slope: influence of boundary conditions and rainfall
No full textThe Vadoncello landslide was mobilized in December 1993 and is still active. It involves highly tectonized soils and is the reactivation of a landslide dragged by a larger landslide at the toe of the slope soon after the 1980 Irpinia (Southern Italy) earthquake. Investigations and monitoring of the Vadoncello landslide were carried out, between 1994 and 1996, within an EC funded research project. The slope has been found to be formed of chaotic successions of soil and rock strata which have been grouped into soil complexes. The soil mechanical properties are shown to be very poor, the deep soils being prone to large plastic straining even due to relatively small loading changes. The soil displacements show that a shallow fast rotational sliding has occurred at the top of the slope and a shallow earthflow has developed downslope, both lying above deeper soils involved in a mechanism of slow and long-lasting irrecoverable movements. These slow deep movements are considered to be consequent to the plastic flow of the clayey soils. They can be activated by the effects of seasonal rainfall, of low-medium intensity seismic events and by the effects of the morphological changes resulting from the slow movements themselves. The landslide reactivation in 1993 is seen to have been the combination effect of a low return-period rainfall event and the slow movements active at depth in the slope.Published165-185JCR Journalope
Structure degradation and changes in the mechanical behaviour of a stiff clay due to weathering
No full textThe paper discusses the results of research into the causes of weathering of stiff Pleistocene clays located in the Montemesola Basin (TA, Italy), and on the effects of weathering on the flay's mechanical behaviour, The weathered clays are yellow-brown and overlie the original grey clays in the whole basin. The liquidity indexes of both the yellow and the grey clays, their fabric, as observed by means of scanning electron microscopy, as well as the yellow clay oxidation features suggest that drying has been the main weathering process in the basin. This is confirmed by the results of drying-wetting cycle tests carried out in the laboratory on undisturbed clay samples, which show the drying-wetting cycles to produce changes in the grey clay similar to those present irt situ due to weathering. Results of oedometer, stress path and triaxial tests show that weathering has caused a degradation of the clay bonding and an associated reduction in the size of the clay state boundary surface. Both one-dimensional and isotropic compression data and the shear data indicate that the effects of weathering on the mechanics of the clay may be established according to the decrease in the clay stress sensitivity. Weathering also causes a decrease in the normalised shear stiffness, as observed by means of bender element tests, which is also related to a decrease in the stress sensitivity
Mechanics of a tectonized soil slope: influence of boundary conditions and rainfall
No full textThe Vadoncello landslide was mobilized in December 1993 and is still active. It involves highly tectonized soils and is the reactivation of a landslide dragged by a larger landslide at the toe of the slope soon after the 1980 Irpinia (Southern Italy) earthquake. Investigations and monitoring of the Vadoncello landslide were carried out, between 1994 and 1996, within an EC funded research project. The slope has been found to be formed of chaotic successions of soil and rock strata which have been grouped into soil complexes. The soil mechanical properties are shown to be very poor, the deep soils being prone to large plastic straining even due to relatively small loading changes. The soil displacements show that a shallow fast rotational sliding has occurred at the top of the slope and a shallow earthflow has developed downslope, both lying above deeper soils involved in a mechanism of slow and long-lasting irrecoverable movements. These slow deep movements are considered to be consequent to the plastic flow of the clayey soils. They can be activated by the effects of seasonal rainfall, of low-medium intensity seismic events and by the effects of the morphological changes resulting from the slow movements themselves. The landslide reactivation in 1993 is seen to have been the combination effect of a low return-period rainfall event and the slow movements active at depth in the slope.Published165-185JCR Journalope
Localized deformation in intensely fissured clays studied by 2D digital image correlation
No full textActa Geotechnica June 2013, Volume 8, Issue 3, pp 247-263 Localized deformation in intensely fissured clays studied by 2D digital image correlation C. Vitone, G. Viggiani, F. Cotecchia, S. A. Hall … show all 4 hide Citations 368 Downloads 200 Citations 9 Comments » Download PDF (3,181 KB) » View Article Abstract This paper represents a further step in a longstanding research on the influence of fissuring on the mechanical behavior of natural clays. The results of an experimental investigation into the influence of fissure orientation on the evolution of strain localization in the intensely fissured scaly clay from Santa Croce di Magliano (south of Italy) are reported. The experimental program involved plane strain compression tests where the effects of the combination of different factors, such as the specimen size and the orientation of fissuring, were investigated. A key aspect to this work is that the standard global stress–strain measurements were augmented by full-field displacement and strain measurements through 2D digital image correlation. Access to incremental strain fields provided information about slight details or anomalies as well as the complexity of deformation processes, which is of crucial importance for proper interpretation of test results at the global, macroscopic level
"Mitigazione del Rischio da Frana per lo Sviluppo Sostenibile e la Tutela dell’Ambiente."
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Experimental investigation of the evolution of elastic stiffness anisotropy in a clayey soil
No full textThe paper presents the main results of a research study into the very small strain shear stiffness of a clayey soil, as measured in vertical and horizontal directions, G(hv) and G(hh), respectively, by means of T-shaped horizontal bender elements fitted in a stress-controlled triaxial system. The testing programme was designed to investigate the evolution of the anisotropy ratio G(hh)/G(hv) along isotropic (eta = 0) and anisotropic (eta not equal 0) virgin radial paths. In particular, a reconstituted clay has been chosen as tested material in order to unequivocally relate the observed evolution of its stiffness anisotropy to the specific stress-strain histories imposed in laboratory. The results show that the small strain stiffness anisotropy smoothly adapts itself to the imposed strain history, achieving different constant values ranging from 1 to 1.2 for eta ranging from 0 to 0.8. The experiments show that the complete modification of the directional elastic properties of the soil requires the virgin radial compression path to be extended along a new direction up a stress level at least four times larger than that experienced previously. Finally, the variations in the clay elastic anisotropy have been related to the changes in clay fabric as investigated by means of scanning electron microscopy. In this context, the variation of the fabric orientation has been quantified through a specific digital image processing
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