3. Experimental determination of sedimentation rates

3.1 Behavior of a suspension in a test tube

If a suspension of sufficient concentration (> 0.5% by volume) is poured into a test tube, the following phenomena are observed (figure 1 ):

• Initially, large grains settle rapidly and settle on the bottom of the sample (zone a). The height of this zone increases rapidly and stabilizes after the settling of sands larger than 0.1 mm;

• an interface between a clear liquid (zone b) and a muddy phase appears rapidly, sometimes immediately. The muddy phase can itself be divided into two parts: an upper part that retains the appearance of...