1,465 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 effects of weathering on the physical and mechanical properties of igneous and metamorphic saprolites
No full textThe present paper presents three extensive datasets of laboratory testing on weathered geomaterials, which are emblematic of soil types widely found worldwide. The overall dataset includes soils originating from igneous and metamorphic rocks, either coarse or fine grained and having either felsic or mafic minerals. In particular, the data are interpreted to highlight the effects that weathering has on the physical and mechanical properties of these natural geomaterials comparing them with published data with the aim to provide a general framework of interpretation that takes into account this geological process and links soil mechanics to engineering geology. Generally, weathering induces a reduction in the grain size, both due to physical actions (e.g. opening of grain contacts) and to the chemical decomposition of minerals resulting in the formation of clay minerals. As weathering proceeds and the soil becomes finer, the in situ specific volume and the location of the normal compression and critical state lines move upwards in the volumetric plane. On the other hand, the clay minerals cause its angle of shearing resistance to reduce. When analysing the behaviour of the intact soil, in all cases positive effects of structure, albeit small compared to some sedimentary soils, were observed and these reduced as a consequence of weathering
The behaviour of a gap graded sand with mixed mineralogy
No full textThe compression and shearing behaviour in mixtures of soils of different granulometries and/or mineralogies has been researched extensively. The focus of the research has been to identify the key factors that might lead the behaviour to change from transitional to not transitional, where transitional behaviour is characterised by non-convergent compression paths and critical state lines that might be non-unique. A review of mixtures of different soils revealed a complex pattern of behaviour, in which transitional behaviour can be caused by relatively small changes in the proportion or nature of the soil particles. It was then assumed that the mineralogy of the matrix composed by larger grains determines the mode of behaviour. If there is a strong and stiff matrix made of quartz sand particles either larger than or at least of a similar size to the other component, then non-convergent compression paths and/or not unique CLSs are likely to occur. This paper presents the results of triaxial and oedometer tests on a range of mixtures of a quartz sand and a carbonate sand, but with a larger weaker carbonate sand component. As predicted, no transitional behaviour was seen in any mixture
Identification and quantification of transitional modes of behaviour in sediments of Venice lagoon
No full textAn analysis was made of an extensive series of oedometer and triaxial tests on intact samples of silts and silty clays from the lagoon of Venice, as well as a more limited series of carefully controlled oedometer tests on reconstituted specimens. The soils appear to have transitional modes of behavior with compression curves that converge only slowly in the v–log s'v plane and critical state lines defined for triaxial compression that are non-unique in the v–lnp' plane. Two means of quantifying the degree of transitional behaviour are introduced, one factor, m, being based on the oedometer data
and the second, P, on the critical state data. The values of m were in general lower than those of P, because of the higher stress level considered. The values of m were also found to depend on unloading, which must be accounted for when comparing data from intact and reconstituted specimens
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