Abstract
This study deals with the behaviour of mixtures of sand and saturated kaolin paste considered as composite materials made of permeable and deformable (with non-linear behaviour) matrix (the kaolin paste) with rigid and impervious inclusions (the sand grains). Oedometric and permeability tests conducted on such mixtures highlight the key role of the state of the clay paste, and show the existence of a threshold of sand grain concentration above which a structuring effect influences both modulus and permeability. At the light of these experiments, the usual and tangent homogenization process (with simplifying assumptions to make the problem manageable) has been applied to estimate the mixture permeability and tangent compressibility. Qualitative and quantitative comparisons with experimental data point out the domain of interest and the limitations of such approaches.
Highlights
Materials made of sand and clay are widely encountered in civil engineering either as common natural soils on which structures are settled, or as reconstituted materials used for road embankment, earth dam, contamination barrier, etc
This is typically an upscaling problem that could in principle be handle in the framework of homogenization methods. The use of such a framework is, made difficult by the strong non-linearity and irreversibility of the compaction process, whose aim is to produce a large reduction in pore volume. It is largely accepted in soil mechanics that, for simple soils like uncemented sand or remoulded kaolin recompacted in the laboratory, the decrease in void volume during compaction is proportional to the logarithm of the effective stress σ following the phenomenological law: e1
Results have been drawn as a function of two volumetric state parameters, the clay void ratio ec and the granular void ratio eg, instead of the overall void ratio parameter classically used in soil mechanics
Summary
Materials made of sand and clay are widely encountered in civil engineering either as common natural soils on which structures are settled, or as reconstituted materials used for road embankment, earth dam, contamination barrier, etc. It is well known that the compressibility highly depends on the nature of the constituents – especially the mineralogical structure of the clay – their relative proportions, as well as the overall density This is typically an upscaling problem that could in principle be handle in the framework of homogenization methods. The use of such a framework is, made difficult by the strong non-linearity and irreversibility of the compaction process, whose aim is to produce a large reduction in pore volume (and to expel water in case of saturated materials). Even in the basic case of a composite made of saturated clay and rigid sand grains, such a non-linear physics including volume variations as an essential feature leads to homogenization problems of high theoretical and numerical complexity. For this reason, simplifying physically based assumptions are of interest to make the up-scaling problem manageable, while catching the key mechanisms at the local scale
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