Collections of Civil Engineering technical info: SOIL CONSISTENCY

Soil consistency is the strength with which soil materials are held together or the resistance of soils to deformation and rupture. Soil consistency is measured for wet, moist and dry soil samples. For wet soils, it is expressed as both stickiness and plasticity, as defined below. Soil consistency may be estimated in the field using simple tests or may be measured more accurately in the laboratory.
Note: in each case, indications will be obtained concerning the relative value of soil for fish-pond construction, particularly when the wet-soil consistency is determined.

Determination of wet-soil consistency

Testing is done when the soil is saturated with water, as, for example, immediately after a good rainfall. First, determine stickiness, that is, the ability of soil materials to adhere to other objects. Then, determine plasticity, that is, the ability of soil materials to change shape, but not volume, continuously under the influence of a constant pressure and to retain the impressed shape when the pressure is removed.

Field test for stickiness of wet soil

Press a small amount of wet soil between your thumb and forefinger to see if it will stick to your fingers. Then slowly open your fingers. Rate the stickiness as follows:

0 Non-sticky, if no soil or practically no soil sticks to your fingers;

1 Slightly sticky, if the soil begins to stick to your fingers but comes off one or the other cleanly and does not stretch when the fingers are opened;

**2 Sticky, if the soil sticks to both the thumb and forefinger and tends to stretch a little and pull apart rather than pulling free from your fingers;

**3 Very sticky, if the soil sticks firmly to both thumb and forefinger and stretches when the fingers are opened.

Field test for plasticity of wet soil Roll a small amount of wet soil between the palms of your hands until it forms a long, round strip like a wire about 3 mm thick. Rate the plasticity as follows:

0 Non-plastic, if no wire can be formed;

1 Slightly plastic, if a wire can be formed but can easily be broken and returned to its former state;

**2 Plastic, if a wire can be formed but, when it is broken and returned to its former state, it cannot be formed again;

**3 Very plastic, if a wire can be formed which cannot be broken easily and, when it is broken, it can be rolled between your hands and be reformed several times.

Determination of moist-soil consistency Field test for moist-soil consistency Testing is done when the soil is moist but not wet, as, for example, 24 hours after a good rainfall. Try to crush a small amount of moist soil by pressing it between your thumb and forefinger or by squeezing it in the palm of your hand. Rate moist soil consistency as follows:

0 Loose, if the soil is non-coherent (single-grain structure);		1 Very friable, if the soil crushes easily under very gentle pressure but will stick together if pressed again;

2 Friable, if the soil crushes easily under gentle to moderate pressure;		**3 Firm, if the soil crushes under moderate pressure but resistance is noticeable;

**4 Very firm, if the soil crushes under strong pressure, but this is difficult to do between the thumb and forefinger;		5 Extremely firm, if the soil crushes only under very strong pressure, cannot be crushed between the thumb and forefinger, but must be broken apart bit by bit.

Determination of dry-soil consistency Field test for dry-soil consistency Testing is done when the soil has been air-dried. Try to break a small amount of dry soil by pressing it between your thumb and forefinger or by squeezing it in the palm of your hand. Rate dry soil consistency as follows:

0 Loose, if the soil is non-coherent (single-grain structure):		1 Soft, if the soil is very weakly coherent and friable. breaking to powder or individual grains under very slight pressure;

2 Slightly hard, if the soil resists light pressure, but can be broken easily between thumb and forefinger;		3 Hard, if the soil resists moderate pressure, can barely be broken between the thumb and forefinger, but can be broken in the hands without difficulty;

4 Very hard, if the soil resists great pressure, cannot be broken between the thumb and forefinger but can be broken in the hands with difficulty;		5 Extremely hard, if the soil resists extreme pressure and cannot be broken in the hands.