Soil index properties are used extensively by engineers to discriminate between the different kinds of soil within a broad category, e.g clay will exhibit a wide range of engineering properties depending on its composition.

The plastic limit is defined as the lowest moisture content of a soil that will permit a sample to be rolled into threads of 3 mm diameter without the threads breaking. The test procedure has remained, in principle, the same since 1932, when Casagrande proposed to define the various limits by relating the moisture content characteristics of soil under certain conditions. The apparatus required is simple yet effective. 

Model No. Desc
24-0430 Glass plate
24-0811 Rod comparator
81-0140 Spatula 200 mm

The condition of a soil can be altered by changing the moisture content. The liquid limit is the empirically established moisture content at which a soil passes from the plastic to the liquid state. A knowledge of the liquid limit allows the engineer to correlate several engineering properties with the soil. Two main types of test are used; the Casagrande type (Cup), which has been used for many years, and the cone penetrometer method, which is now the definitive method specified in BS 1377.

Particular design features of the instrument include a positive action horizontal lead screw, which is rapidly adjustable and rigidly fixes the height of cup in relation to the base during the test procedure. The cam mechanism and cup suspension assembly have been designed to withstand constant use with minimum readjustment

Model No. Desc BS/EN ASTM AASHTO
24-0425 Grooving tool Yes - -
24-0434 Liquid limit device - Yes Yes
24-0410 Liquid limit device Yes - -
24-0453 Grooving tool - Yes -
24-0461 Grooving tool - - Yes
24-0417/01 Liquid limit device - motorised Yes - -
24-0430 Glass plate Yes - -

•Reduces operator error
•Applicable to a wide range of soils
•Gives reproducible test results
•Provides direct measurement of penetration

The method is fundamentally more satisfactory than the Casagrande method as it is essentially a static test depending on the soil shear strength. The test is based on the relationship between moisture content and the penetration of a cone into the soil sample under controlled conditions.

Determines the moisture content at which clay soils pass from a plastic to a liquid state.

Model No. Desc
24-0540 Cone Penetrometer
24-0548 Penetration test cup
24-0544 Test cone
24-0546 Test gauge

Model No. BS 1377 BS 1924-2 Voltage Weight, kg
24-0545/01 Yes Yes 220-240 V 50/60 Hz 8.6

When the water content of a fine-grained soil is reduced below the plastic limit, shrinkage of the soil mass continues until the shrinkage limit is reached. Shrinkage can be significant in clays but less so in silts and sands. The equipment listed enables the engineer to determine a number of important parameters, including shrinkage ratio, volumetric shrinkage and linear shrinkage.

This method of test covers the determination of the shrinkage limit, shrinkage ratio, volumetric shrinkage and linear shrinkage.

Model No. Desc
82-0380 Measuring Cylinder - Glass
82-2000 Evaporating dish
24-1600 Glass cup
24-1550 Shrinkage dish
24-1500 Prong plate

This test covers the determination of linear shrinkage of soils and indicates the plastic properties of soils with a low clay content.

Model No. Desc
24-1800 Shrinkage mould
81-0588 Vernier caliper

Particle density or specific gravity is a measure of the actual particles which make up the soil mass and is defined as the ratio of the mass of the particles to the mass of the water they displace. A knowledge of the particle density is essential in relation to other soil tests. It is used when calculating porosity and voids ratio and is particularly important when compaction and consolidation properties are being investigated. The majority of apparatus used for the various tests is general laboratory equipment.

This method is suitable for soils containing up to 10% of particles retained on a 37.5 mm BS sieve.

Model No. Desc
24-2854/01 Mechanical end-over-end shaker
24-2830 Gas jar

These methods are generally suitable for fine-grained soils. The larger pycnometers are not usually suitable for clay soils.

Model No. Desc Capacity, ml
24-2900 Density bottle 50
24-2950 Density bottle 100
24-2885 Pyknometer -
24-2890 Density bottle 25