8/11/2019 Simple Field Tests to Determine Soil Properties

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mple field tests to determine soil properties

ARNING ELEMENT OBJECTIVES

fter you have learned this element you should be able to:

carry out three different preliminary tests to roughly determine the nature of the soil;

carry out two tests to determine the proportions of the coarse and fine particles in a sample and one test to roughly determ

e quantity of silt and clay present in the finest fraction;

describe how fractions of soil are classified according to grain sizes;

carry out two tests to determine whether a fine-grained soil contains mainly clay or silt.

is possible to say a lot about a soil by only looking at it and touching it. Before any other tests are carried out the following

eliminary identification should be made:

Grain sizes. Is the soil mainly coarse or fine? Try to separate the coarse particles from the fine ones and roughly estimate wh

ercentages are coarse/fine. Press the big particles between your fingers to find out if they consist of many small particles bo

gether (e.g. hard lumps of clay).

Organic material. Does the soil contain many fibres or small roots? Does it look dull or dirty? When the soil smells earthy or

ants, it is likely to be organic. This odour will become more distinct when the sample is heated.

Silt/clay or sand/gravel. Dry soils which contain a large percentage of sand/gravel feel coarse and gritty, while dry clay feels

nd smooth. Dry silt feels floury and will disintegrate into a fine powder when rubbed. When wet, sand/gravel will not stick to

ngers; while wet clays and silts feel sticky and will stain the fingers.

nce the particle sizes determine to a great extent the properties of a particular soil, the first tests we will discuss deal with t

pect. Particles are classified according to their size into fractions (gravels, sands, clays, or silt).

able 1 shows the sizes and basic characteristics of these fractions.

able 1

action Grain size

(mm)

Shape Cohesion Plasticity Permeability ConsolidationVolume

change

Effect in a soil mixtu

Max. Min.

ones 60 2 Various None None High Little None Contributes to stabi

and strength

nd

oarse 2.0 0.6 Angular Apparent None High to Slight Slight Contributes to

medium 0.6 0.2 and when damp medium strength and

ne 0.2 0.06 rounded stability

t 0.06 0.002 Angular and

rounded

Very slight Slight to

medium

Medium to

low

Slight Medium Contributes to insta

especially when vibr

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or wet

ay 0.001 0.005 Plates,

sometimes

rods

Considerable High Low High Considerable Contributes to stren

cohesion, but to inst

due to plastic movem

under pressure