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3.2. LABORATORY TESTS 27
3.2 Laboratory tests
3.2.1 Granulometric composition
The granulometric composition specifies the relative proportions by weight of various particle
sizes in the soil. A sieve analysis is carried out for particle diameters > 0.06 mm, a sedimentation
or hydrometer analysis for particle sizes smaller than approx. 0.1 mm. A soil can be
classified as a clay, silt, sand or gravel according to the grading curve. Mixed-particle soils are
designated according to their principal soil type. Soils that are essentially influenced by their
physical properties are known as non-plastic or granular. Soils are termed cohesive when their
soil mechanics properties are essentially dependent on the electrochemical forces between the
particles, and clay minerals are particularly prevalent here. The average gradient of the grading
curve indicates whether the soil has a uniform or non-uniform composition. The uniformity
coefficient U is defined as
U = d60
(3.2)
d10
where d60 designates the particle diameter for 60% passing through the sieve, d10 the corresponding
designation for 10%. Soils with U