1,721,001 research outputs found
The effects of weathering on the physical and mechanical properties of a granitic saprolite
No full textLess research has been carried out on the changes induced by weathering to the mechanical properties of reconstituted and intact soils that originate from chemical decomposition of rocks (saprolites) than has been done for sedimentary soils. One-dimensional compression and triaxial testswere performed on reconstituted and intact specimens along aweathered profile to investigate the changes in their physical and mechanical properties. Some heterogeneity in the weathering tends to cloud the trends observed, but it was still clear that the grading varies the most, while the mineralogy changes less and the particle morphology is nearly unchanged. The gradient of the normal compression line is fairly constant with weathering, but reduces significantly at shallower depths. The gradient of the critical state line in the stress plane reduces with weathering, while its intercept in the volumetric plane has a more complex trend, but generally also reduces with decreasing depth. The value of the specific volume in situ increases with weathering and so the in situ state becomes closer to the critical state line. The effects of structure were quantified using a pseudo strength sensitivity defined by the location of the intact state boundary surface at the critical state. This parameter generally reduces with weathering and increases with depth
Experimental accuracy of the initial specific volume
No full textMany advanced soil models rely on the current state relative to normal and critical state lines to describe soil behavior. The position of these lines, therefore, requires an accurate estimation of the specific volume or void ratio. A series of one-dimensional compression tests was performed both on a coarse and a fine grained soil to investigate the experimental accuracy of the initial specific volume. This was obtained comparing independent calculations of the initial specific volume that were based on redundant measurements of height and weight of the specimen, both at the beginning and at the end of the test. The redundancy in the measurements was a key factor to obtain independent calculations. It was found that the excess water, such as may be stored in the filter papers, was the main cause of inaccuracy, when gross errors did not occur. Two novel confining rings having a closed-base were designed to reduce this effect. Although this was possible for the coarse grained soils tested, the fine grained soils retained more water due to the higher suction at the end of the test and water adsorption could not be avoided. The assumption of saturation is shown to be far from accurate, meaning that both the bulk unit weight and the water content should be measured independently to obtain a reliable measurement of the specific volume. The specific volume of the intact soil was found to be less accurate than when reconstituted. The experimental scatter was compared with the theoretical accuracy obtained from the error propagation theory. Good agreement was found between the theoretical and experimental accuracy. © ASTM Int'l
THE BEHAVIUOR OF SUB-SOILS FROM THE PO RIVER EMBANKMENTS: AN EXAMPLE OF TRANSITIONAL BEHAVIOUR IN NATURAL SOILS
No full textA series of triaxial and oedometer tests has been analysed on highly heterogeneous alluvial sediments from the flood plain of the River Po in Italy. It is shown that the framework applicable to behaviour of the soils may be correlated with the grading and that as the fines content reduces the mechanics change from a clay type of behaviour that follows the key assumptions of Critical State Soil Mechanics to a transitional mode in which many of these assumptions break down. This transitional behaviour has only previously been seen for a variety of reconstituted soils, including some taken from the same site, and even if the data are imperfect, they provide the first evidence of transitional behaviour in soils with their natural geological fabric
Comportamento compressivo dei terreni argillosi sottostanti al sito archeologico di Sibari
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The mechanics of an Italian silt: an example of "transitional" behaviour
No full textBy controlling the particle size distribution of an Italian silt, the influence of grading on its behaviour was investigated. As the clay content was reduced, the behaviour changed from a typical clay mode to a transitional form between that of clays and sands that had previously been seen only for gap-graded soils, emphasising that this type of behaviour is possibly much more extensive than previously thought. The work has highlighted several features of transitional behaviour, and in particular that unique normal compression and critical state lines do not exist, that Rendulic’s principle does not apply, and that drained and undrained tests do not reach unique ultimate states
Indagine al microscopio elettronico sulla microstruttura del limo argilloso degli argini del Po.
No full textEffetto di mineralogia e granulometria sul comportamento di transizione di miscele di sabbia.
No full textIl comportamento di transizione è stato identificato per diverse tipologie di terreno, dai terreni con lacuna granulometrica a limi e sabbie ben gradate. Tale comportamento è caratterizzato dall’esistenza di percorsi di compressione non convergenti e dalla non unicità della linea di stato critico, con localizzazione fortemente dipendente dalla densità iniziale dei campioni. Sebbene in letteratura tale comportamento sia stato inizialmente attribuito a terreni di granulometria intermedia, è stato mostrato come questo sembrerebbe manifestarsi anche in presenza di terreni aventi granulometria mista, con lacuna granulometrica o ben gradati, e per miscele composte da particelle di diversa natura o diversa mineralogia. La diversa tipologia di terreni in cui tale comportamento è stato osservato evidenzia l’elevata difficoltà nell’individuazione dei fattori chiave che lo determinano. Uno studio recente ha mostrato la mancata convergenza dei percorsi di compressione per alcune miscele di sabbia create artificialmente utilizzando materiali di differente mineralogia: sabbia di quarzo e sabbia carbonatica. Con lo scopo di verificare l’effetto della composizione mineralogica, delle dimensioni e resistenza relative dei grani e natura delle particelle sul manifestarsi o meno del comportamento di transizione, la presente nota approfondisce i risultati del precedente studio utilizzando miscele di sabbia caratterizzate da proporzioni variabili delle componenti mineralogiche e granulometriche
Assessment of the effects of the structure on the compression behaviour of a young alluvial silty soil
Full text linkA comprehensive series of tests was performed to investigate the effects of the in-situ structure and sample preparation technique on the compression behaviour of a shallow young alluvial silty soil. Two different particle size distributions were investigated by testing intact, compacted, and slurry samples in an oedometer. The compression of the slurry samples, created at different initial water contents, gave a unique intrinsic compression line for one of the two distributions. This was used as a reference for analysing the effects of the structure of the compacted and intact specimens. The compacted samples were prepared by means of static and dynamic compaction in one or more layers with vertical holes simulating those created by plant roots in natural samples. The results showed that a unique normal compression line is defined regardless of the number of layers or the number of holes, with a clear effect of the structure when compared to the slurry samples. The significant effects of the in-situ structure of the intact samples were observed even at high stress levels. An important finding was the non-uniqueness of the compression line for the second distribution. For the case of the slurry samples, the compression lines remained parallel to each other even at high stress levels, whereas a unique line was found for the compacted samples. These results are contrary to those often given in the literature, namely, that the sample preparation technique can create very robust initial structures resulting in a mode of behaviour that has been called “transitional”. The research also emphasises how the quantification of the natural structure is critically dependent on the way in which the intrinsic samples are prepared
Studio litostratigrafico e geotecnico della piana di Sibari con riferimento all'evoluzione morfologica e ambientale del sito archeologico
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