86,769 research outputs found
Un laboratorio integrato finalizzato allo studio delle colate di fango in terreni piroclastici
No full textBioactive compounds from marine-derived aspergillus, penicillium, talaromyces and trichoderma species
No full textThe impact of bioactive compounds from natural sources on human life, particularly in pharmacology and biotechnology, has challenged the scientific community to explore new environmental contexts and the associated microbial diversity. [...]
Effects of moulding water content on the behaviour of an unsaturated silty sand.
No full textUnsaturated soils can be often encountered in practical applications. In particular, even though index properties of a soil as construction material are left unchanged, the compaction procedure (moulding water content, compaction energy, etc.) influences the mechanical response of the resulting material, its after compaction degree of saturation (i.e. suction) and, more generally, the earth constructions behaviour (Vinale et al., 1999). This paper tries to contribute to the discussion of the above mentioned aspects of soil behaviour presenting the results of a series of suction controlled triaxial tests performed on an optimum water content and wet of optimum compacted soil. Details on the used apparatus are reported in Rampino et al. (1999). The experimental program was conceived in order to analyse the effects of both suction and fabric on soil behaviour. Overall, it consisted of 23 tests, i.e. isotropic compression, constant mean net stress (p-ua) shear and “standard” shear tests, all carried out under drained conditions and constant suction. The investigated suction levels were 0, 100, 200, 300 kPa for the optimum compacted soil and 0, 100, 200 kPa for the wet compacted material. The optimum and the wet compacted specimens exhibited very different behaviour in all the stages of the tests. For example, during the equalisation stages, the optimum material swelled and absorbed water, while the wet soil shrunk and expelled water. This behaviour is explained by the measurements of the after compaction suction (ua-uw)o. Using the Imperial College tensiometer (ua-uw)o was measured as high as 800 kPa for the optimum material (then causing wetting during equalisation) and as low as 60 kPa for the wet specimens (then causing drying during equalisation) – a relevant effect of moulding procedure. The results of the isotropic compression tests highlight a strong effect of suction on soil compressibility. In particular, the compressibility index decreases about 25% from 0 to 200 kPa of suction. The greatest amount of this effects occurs in a limited suction range (0-100 kPa) while tends to a threshold value for (ua-uw) greater than 200 kPa. Comparing experimental findings on the optimum and the wet specimens, it is observed that an increase in moulding water content induces a severe increase in compressibility. In addiction, data indicate that both the shape and the position of the after compaction loading-collapse loci (LC) are largely affected by moulding water content. Thus, soil susceptibility to collapse strongly depends on preparation water content. The data of shear tests show that suction significantly affects large strain shear stiffness and resistance. For instance, in the range 0-200 kPa of suction, the strengthening with (ua-uw) is expressed by an apparent cohesion varying from 0 to 200 kPa for the optimum and from 0 to 150 kPa for the wet compacted soils. The results seems to be well grouped for suction levels and can be interpreted by straight fitting lines having the same M coefficient in the q:(p-ua) plane. The effect of moving from the optimum to the wet compaction water content is then a decrease in stiffness and in apparent cohesion, as well as a reduction of the size of the after compaction yield surface. The large series of experimental results obtained on Metramo silty sand can be satisfactorily modelled by the modern theories for unsaturated soils (Alonso 1990, Wheeler & Sivakumar 1995), if it is assumed that the different preparation procedures yield to different soils. The influence of suction and moulding water content on the observed behaviour clearly emerged in all the tests phases and highlights the need of carefully considering these two variables in handling engineering problems involving compacted soils as construction materials
Effects of net stress and suction history on the small strain stiffness of a compacted clayey silt.
No full textAn experimental study was carried out to investigate the effects of the mean net stress and suction history on the initial shear stiffness, G0, of a compacted clayey silt. Isotropic tests were performed using two suction-controlled devices, a triaxial cell and a resonant column torsional shear (RCTS) cell, so as to investigate the volumetric behaviour of this material. As for saturated soils, one can expect to find a strong correlation among stress history, volumetric state, and G0. Initial shear stiffness was measured almost continuously along various isotropic stress paths, including compressions and drying–wetting single stages or cycles, by using the RCTS cell. The collected data demonstrate a strong dependency of G0 on mean net stress (p – ua) and suction (ua – uw). Cycles of suction, in particular increasing suction beyond the past maximum value, induce significant accumulation of irreversible strains and increase of stiffness, confirming that G0 is not univocally related to the stress state (p – ua, ua – uw).Key words: unsaturated, compacted, small strain, stiffness, volumetric behaviour, stress history
Modelling the influence of stress-strain history on the initial shear stiffness of an unsaturated compacted silt.
No full textThis is the follow-up paper to Vassallo et al. (2007), which discussed the experimentally observed small-strain behaviour of an unsaturated compacted silt. The influence that suction and, more in general, mean net stress – suction history has on the initial shear stiffness was analysed and ascribed to the accumulation of irreversible volumetric strains. In this study, a model able to predict the observed behaviour is proposed, based on classical unsaturated soil volumetric hardening elastoplastic formulations. Starting from the interpretation of the results relative to simple stress paths, such as preliminary equalization and loading–unloading compression, the results of "complex" stress paths, such as those including drying–wetting cycles, have subsequently been modelled by introducing some additional parameters.Key words: unsaturated, compacted, small strain, stiffness, volumetric behaviour, stress history
Effectiveness of trenches filled with geomaterials in the reduction of surface vibration amplitudes.
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