Mechanical analysis is the determination of grain sizes and the percentage distribution of each size. A complete mechanical analysis is accomplished in two parts: sieve analysis and hydrometer analysis.

A sieve analysis is applicable to soils that are larger than the No. 200 sieve or that contain small amounts of material passing the No. 200 sieve. You can conduct the sieve analysis either on the entire sample or on the sample after the fines are removed by prewashing. The apparatus and procedures used to conduct a sieve analysis are described below.

APPARATUS. Typical sieve analysis apparatus includes a gram weighing balance and a number of sieves with apertures of varying sizes used to determine grain sizes (fig. 15-29). Sieves may be of the ordinary circular SIFTER type (usually about 8 in. in diameter) or the ROCKER type, which consists of a rocker frame in which screens with apertures of various sizes can be placed.

The sieve used for analysis is the so-called standard sieve. A standard sieve has a square aperture. Screen sizes are designated as follows: A sieve with fewer than four apertures to the linear inch is designated by the size of an aperture; for example, a 1/4-in., 1/2-in., 3/4-in., or 1-in. sieve. A sieve with four or more apertures to the linear inch is designated by a number that represents the number of apertures to the linear inch. A No, 4 sieve, for example, has four apertures to the linear inch, a No. 6 has six apertures, and so on. The finest sieve used is a No. 200, with 200 apertures to the linear inch and an aperture size slightly smaller than one two-hundredth of an inch square.

To conduct a sieve analysis, you need an electric or hand-operated sieve shaker.

The hand-operated shaker is shown in figure 15-30.