Smith's Elements of Soil Mechanics. Ian Smith
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Название: Smith's Elements of Soil Mechanics

Автор: Ian Smith

Издательство: John Wiley & Sons Limited

Жанр: Отраслевые издания

Серия:

isbn: 9781119750413

isbn:

СКАЧАТЬ on each sieve is determined and subtracted from the percentage passing through the previous sieve. This gives the percentage passing through the current sieve.

      Calculations may be set out as follows:

Sieve size (mm) Mass retained (g) Percentage retained Percentage passing
10 0 0 100
6.3 5.5 5 95
2 25.7 22 73
1 23.1 20 53
0.600 22.0 19 34
0.300 17.3 15 19
0.150 12.7 11 8
0.063 6.9 6 2
Pass 0.063 2.3 2
∑115.5 g
equation Schematic illustration of the particle size distribution curve. equation

      It is also seen that the grading curve has a regular slope and therefore contains roughly equal percentages of particle sizes. The soil is a medium graded, gravelly SAND.

      1.5.4 Sedimentation analysis

      The fraction of soil smaller than 0.06 mm cannot be separated by sieves, so a sedimentation analysis is used to establish the proportions of silt and clay fractions. The procedure is only considered necessary if more than 10% of the soil passes the 63 μm sieve. In the test, a sample of the dry soil passing the 63 μm sieve is placed into suspension with water in a sedimentation cylinder and allowed to settle over a period of time. Measurements of the percentage of particles remaining in suspension at set time intervals are established by either using a pipette or a hydrometer. Details of the test procedures are given in BE EN ISO 17892‐4:2016 and Head (2006). The pipette procedure is described below.

Schematic illustration of pipette analysis arrangement.

      The pipette has a standard volume of 10 ml. This equals the volume of the solution sampled. That sample is flushed from the pipette into a small glass weighing bottle. By weighing the bottle before sampling and again after oven drying, the mass of the sampled soil is determined. By scaling the mass retained in the pipette sample (10 ml), less the mass of the dispersant, to that of the cylinder (500 ml), the mass of soil in suspension is determined. That, together with the determination of the particle size at the time of sampling, allows us to establish the percentage of particles passing that size.

      The particle size, d (mm), sampled at depth, h (mm), at time, t (min) is established by:

      (1.4)equation

       η is the dynamic viscosity of water (mPa s) (=0.89 at 25 °C)

       ρs = particle density of the soil (Mg/m3) – see Section 1.7.3.

      If samples are taken at 4, 46 and 414 minutes for a soil with particle density of 2.65 Mg/m3, the particle sizes in each sample will be 0.02, 0.006 and 0.002 mm respectively.

      The results of a standard pipette analysis, carried out on a sample of soil passing the 63 μm sieve of dry mass 27.25 g and particle density = 2.65 Mg/m3, were:

Sample 1 Sample 2 Sample 3
Time (min) 4 46 414
Mass of empty sample bottle (g) 5.1926 5.3710 5.2983
Mass of sample bottle plus dry soil (g) 5.6927 5.8052 5.6898

      During a control test on the dispersant/water only solution (500 ml), it was established that the mass of dry dispersant in a sample of 10 ml was 0.0173 g.

      Determine the percentages of fine silt and clay in the soil.

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