Читать книгу The Rheology Handbook - Thomas Mezger - Страница 99

Debris and mud avalanches are an inhomogeneous mixture of water, fine sediment (max. particle size up to d = 0.1 mm), mud (clay, silt, sand, with 0.1 mm < d < 20 mm), and larger “particles” (granules, gravel, stones, boulders, up to d = 20 cm or even 1 m, – which ideed was a little bit too large for a normal rheometer …). They may show mean velocities of v = 1 to 30 m/s, thus, more than 100 km/h. Considering a longitudinal section, two zones of the velocity distribution occur: In the lower range close to the bottom a shear zone showing clearly increasing velocity values from the bottom upwards (i. e. flowing layers showing a velocity gradient), and above a zone close to the surface of almost constant velocity (i. e. v = const, showing “plug flow”) [3.37]. For corresponding rheological tests of dipersions showing particel size up to 10 mm, a ball measuring system can be used (see Chapter 10.6.5). Shear experiments on bulk solids and powders are described in Chapter 13.