NOUVELLE MÉTHODE DE DÉTERMINATION DE LA SPHÉRICITÉ DES SÉDIMENTS MEUBLES

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SUMMARY

A new method to determine the sphericity of mobile sediments

In this paper we show a new method to determine the sphericity of sand particles with sedimentary analysis. We use two different sieves: the one with open squares: the side is a and the diagonal d=a√2 the other with circular openings: the diameter is D. Experimentation shows that elements crossed the open-square sieves in diagonal positions. When we reported the cumulative curves into arithmetic or semi-logarithmic graphs, we used the value d and not the side square a.

A sediment C, which is composed of not very angular or subspherical par- ticles, is represented by two cumulativecurves on the same graph. If a sediment A is very angular, the two curves are disconcerted. The sediment B is subspherical, the difference between the two curves is maximum. We call this difference δ which is equal to dD. For C this difference is Δ, which is always inferior to δ. The absolute sphericity index Sa is the ratio AId in yo. When the particles are very angular, sphericity values are 0—like A and when they are sphericals the index is 1—like B. This index is determined with graphic solutions. The values obtained are compa- rable with those of visual charts.

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