GB2443537A - Measuring plastic properties of a substance, eg soil - Google Patents

Abstract

The invention relates to an apparatus and method for the measurement of a plastic property, eg plastic limit or toughness, of a substance eg soil. The apparatus comprises (i) a base 10 for receiving a sample 23 of the substance; (ii) rolling means for rolling the sample over a known distance; (iii) pressure means 44 for applying a known force to the sample during rolling so as to cause compression of the sample; and (iv) measurement means 22 for measuring the compression of the sample. The sample may be a thread 23 of soil which is rolled repeatedly between upper and lower plates 13, 19 while fixed and movable weights 41,44 apply a known average force to the soil sample. The limits of rolling traverse is defined by end stops 37,55. The diameter of the soil thread is measured by a dial gauge 22. Rolling continues until the soil thread diameter is reduced to eg 3mm or less or until the thread 23 collapses or fractures. The total work done to change the thread diameter from eg 6mm to 3mm may be defined as the toughness of the soil at a given moisture content.

Description

Apparatus and method for measuring plastic properties The present

invention relates to an apparatus and a method for the measurement of a plastic property of a substance, in particular the plastic limit and/or toughness of a substance such as soil.

it is standard practice in ground investigation work, to determine the plastic limit of a substance such as soil in order to identify a soil type and provide a classification of the soil. For example, when building foundations or constructing earth structures in construction work, the plastic limit of soil is measured to provide an indication of the shrinkage and swelling properties of the soil, the compressibility and strength of the soil and the suitability of the soil for various construction purposes. In the UK, this test is required for several national specifications, such as the Highways Agency, National House Builders Council and the Environment Agency.

The "plastic limit" of a substance is defined as the moisture content at which the substance (such as soil) becomes too dry to be in a plastic state. The plastic limit therefore describes the lowest moisture content at which a substance is plastic. Below the plastic limit, the substance behaves in a brittle maimer.

The plastic limit of a substance such as soil currently is typically determined using a procedure devised in 1911 by A. Atterberg, a Swedish soil scientist. The procedure involves drying the soil to near its plastic limit by air drying, moulding it into a ball and rolling it between the palms of the hands. When the soil is near its plastic limit, a thread of about 6 mm diameter and about 50 mm long is rolled over the surface of a smooth, glass plate beneath the fingers of one hand with a backward and forward movement and just enough rolling pressure is applied to reduce the thread to a diameter of about 3 mm (typically taking between five and ten forward and backward movements). If the soil remains intact and does not shear at this stage, then it is dried further by rolling it into a ball and the test is repeated until the thread crumbles or shears both longitudinally and transversely at the 3 mm diameter. The soil is then considered to be at its plastic limit and its moisture content is determined. This moisture content is given as the plastic limit of the soil. This procedure is described in chapterS of the British Standard BS 1377:Part 2: 1990 for UK use (see British Standards institution (London), 1990, BS 1377: British ) Standard methods of test for civil engineering purposes, Part 2: Classification Tests) and in ASTM D43l8-98 for use in the USA (see ASTM 2000, Standard test methods for liquid limit, plastic limit, and plasticity index of soils, D43l8-98, Annual Book of ASTM Standards, volume 04-08, American Society for Testing and Materials, Philadelphia, PA).

The same procedure is described in the National Standards of most other countries.

For these tests, applicable in the construction industry, the moisture content is defined as the ratio of the weight of water in the substance to the weight of dry substance. In the ceramics industry a different definition may be used of the ratio of the weight of water in the substance to the weight of wet substance. References herein to the moisture content preferably are to moisture contents defined as the ratio of the weight of water in the substance to the weight of dry substance, particularly determined using the procedure described in BS 1377:Part 2:1990.

The procedure devised by Atterberg and currently adopted has numerous disadvantages in use. For example, the results of the procedure are dependent on the size, roughness and pressure of the operator's hand. Additionally the assessment by the operator of the crumbling state is highly subjective and the accuracy of the thread diameter at 3 mm is difficult to judge and control. Additionally, different soils behave differently during the procedure. Higher plasticity (heavy) clays may not crumble easily, becoming quite tough at this low moisture content, whereas for lower plasticity clays it may be difficult to produce a 3 mm thread without premature crumbling.

The British Standard guidelines acknowledge these disadvantages and state that it is recognised that the results of the Atterberg procedure are subject to the judgement of the operator, that some variability in results will occur and that it is often difficult to obtain the correct crumbling condition with soils that are marginally plastic. The American ASTM D43 18-98 guidelines, which describe a similar hand rolling plastic limit test procedure, also recognise these disadvantages and state further that the amount of hand or finger pressure required will vary greatly according to the soil being tested, that is, the required pressure typically increases with increasing plasticity. Strictly the required pressure increases with increasing toughness. A report (Sherwood, P. T., 1 970, The reproducibility of the results of soil classification and compaction tests. T.R.R.L. Report LR 339, Department of Transport, Crowthorne, Berkshire) has revealed that for a range of ) soils with plastic limits ranging typically between 15 and 30% and tested by different operators in different laboratories, one-third of all the results obtained were more than 3 units of moisture content (i.e. 3%) from the mean value. Given the significant importance of this test result, this poor accuracy is not acceptable.

The American ASTM D43 18-98 guidelines describe a second method for determining plastic limit, using a rolling device disclosed in US-5,027,660. The rolling device comprises two acrylic plates between which a thread of soil is rolled until the soil thread reaches a diameter of about 3.2 mm (1/8 inch). The bottom plate is stationary and the top plate is moved by hand. The plastic limit is defined as the moisture content when crumbling of the soil thread occurs at the diameter of 3.2 mm. The rolling device aims to ensure that the final diameter of the soil thread is 3.2 mm. It is stated (see Bobrowski, L. J. and Griekspoor, D. M., 1992, Determination of the plastic limit of a soil by means of a rolling device. Geotechnical Testing Journal, vol. 15, no. 3, p. 284-287) that it is critical that paper is attached to both plates to eliminate sliding of the thread of soil and to expedite the drying process. However, allowance must be made for the thickness of the paper attached to the plates and no advice is given on how the paper should be securely attached and kept flat nor whether it must be replaced for each test. Because of the paper the thread cannot be viewed during the rolling process. In practise it has been found that the paper absorbs moisture from the surface but not the middle of the soil thread, resulting in changes in moisture content during the test and non-uniform moisture distribution.

Furthermore, the downward force on the top plate required to reduce the soil thread diameter is applied by the operator, it is not controlled and will vary. This procedure still relies on the subjective determination by the operator of the crumbling stage. Correlation testing using the rolling device shows that the results from the rolling device are comparable with the hand rolling method but the result is still dependent on the operator.

Three different laboratories using the apparatus gave correlation coefficients (r2) of 0.59, 0.73 and 0.95.

in both the construction and the ceramics industry, there is no quantifiable measure for the toughness of a substance, such as soil and particularly clay. A subjective assessment of toughness is given in the British guidelines (see British Standards Institution, 1999, BS 5930: Code of Practice for Site Investigations. Clause 43.3.3. British Standards Institution, London) by referring to the character of a thread of moist soil when rolled on the palm of ) the hand, moulded together, and rolled again until it has dried sufficiently to break at a diameter of about 3 mm (as in the plastic limit test). The guidelines state that in this condition, inorganic clays of high plasticity are fairly stiff and tough; those of low plasticity are softer and more crumbly. A measure of the toughness of a substance would be of considerable benefit, particularly in the ceramics industry, for the purposes of assessing mouldability of substances, such as pottery substances, and in the construction industry for applications where clays are reworked such as clay liners and barriers, clay cores in dams and puddle clays.

The "toughness" of a substance can be defined as the amount of work required to remould the substance in its plastic condition. For metals, the corollary is the ductile-brittle transition over a range of temperatures. For temperatures above the transition a metal is ductile and tough and for temperatures below the transition a metal is brittle with little toughness.

Thus, there remains a need for an apparatus and a method for measuring a plastic property (especially the plastic limit and/or toughness) of a substance that does not rely on operator characteristics and judgement and that will provide accurate and reproducible results. The apparatus and method also should be easy and convenient to use.

Accordingly, the present invention provides an apparatus for the measurement of a plastic property of a substance, the apparatus comprising: (i) a base for receiving a sample of the substance; (ii) rolling means for rolling the sample over a known distance; (iii) pressure means for applying a known force to the sample during rolling so as to cause compression of the sample; and (iv) measurement means for measuring the compression of the sample.

The apparatus of the invention meets the objectives set out above. In particular, the apparatus allows for a standardised procedure to be conducted so as to determine the plastic properties of the substance in an accurate and reproducible manner. For example, the apparatus does not rely on operator characteristics and judgement and is easy and convenient to use. )

By the term "plastic property" is meant a property of the substance that is linked to its plasticity and/or ductility. For example, the apparatus of the invention may be used to determine the plastic limit andlor the toughness of the substance. Thus, the apparatus of the invention is particularly advantageous because it can be used to measure toughness, whereas the prior art apparatus discussed above cannot.

As discussed above, the "plastic limit" of a substance is the lowest moisture content at which the substance is plastic.

The toughness (1) of a substance is defined as the cumulative work done per unit of volume in reducing the sample width by compression; preferably in reducing the sample width from 6 mm to 3 mm. For example, the toughness (T) of a substance may be defined as the cumulative work done per unit of volume for a set number (such as one hundred or ten, especially one hundred) of cycles of compression/tension to a sample of the substance in reducing the sample width; preferably from 6 mm to 3 mm.

A number of different values can be quoted in relation to toughness. is defined as the value of toughness of the substance when at the plastic limit. Thus this is the maximum amount of work that can be applied while the soil is still plastic. Toughness coefficient (Ta) is defined as the rate of change of toughness per unit change of moisture content.

Toughness limit (TL) is defined as the moisture content at which the toughness of the substance is zero. Hardening limit (HL) is defined as the moisture content at which the gradient of a plot of toughness versus moisture content changes. It is typically the moisture content at which the substance changes from a mainly strain hardening material to a mainly strain softening material. TH is defined as the value of toughness at the hardening limit (HL). Toughness index (TI) is defined as the difference in moisture content between the toughness limit and the plastic limit.

Toughness (T), toughness at the plastic limit toughness coefficient (Ta), toughness limit (IL), hardening limit (HL), toughness index (TI) and TH are parameters that may be used in the construction industry as measures of the compactability and resilience of a soil, in the ceramics industry as measures of the workability and mouldability of pottery substances and in the food and phannaceutical industries as measures of the extrudability of food and pharmaceutical substances. Thus, an apparatus and method that may be used to detennine the toughness of a substance has many applications in use.

The apparatus of the invention may be used to determine the plastic properties of any suitable substance. In particular, the substance may be a soil, especially a cohesive type soil. As the skilled person would appreciate, the term "soil" includes earth substances such as clays, silts, sands and other fine particulate substances, peats and other organic substances, limes, pozzolans (by which is meant earth/clay type substances such as volcanic ash used to make cement, by mixing with lime), and mixtures thereof. The substance may alternatively be selected from putties, mortars, cements, pastes, emulsions, sludges, waxes, gels, and mixtures thereof, and/or substances such as food and pharmaceutical substances.

As the skilled person would appreciate, the term "clay" includes natural clays that would be considered a type of soil since they are present in the ground and are unprocessed (of particular importance to the construction industry), as well as clays (referred to as raw clay, plastic clay or ball clay) that have been extracted from the ground and then processed (for example dried, sieved, graded and/or blended) to produce a pottery substance (of particular importance to the ceramics industry). Thus, the substance (such as soil) may be tested in its natural state or after processing of any suitable kind.

The apparatus of the invention may be used to measure the plastic properties of a substance in any suitable form, for example over a range of consistencies from a very soft condition to an increasingly stiff condition. When the substance is a soil, the apparatus preferably is used to measure the plastic properties of the soil wherein that soil is tested at a range of different (measured) moisture contents, especially a range of decreasing moisture contents.

The sample of the substance to be received by the base may take any suitable shape or form, provided that it is of a shape or form that can be rolled over a known distance.

Typically, the sample is of a generally cylindrical shape (known in the art as a "thread").

By "compression" of the sample is meant the reduction in a dimension, such as the width, of the sample caused by the rolling procedure and the application of the known force. For ) example, when the sample is of a generally cylindrical shape, the diameter of the cylinder is taken to be its width.

In one aspect, the base comprises a first plate and the pressure means comprises a second plate, the second plate including control means for modifying the known force exerted at a given position by said second plate against a sample positioned between said plates.

Preferably, the first and second plates are substantially parallel to one another. By "substantially parallel" is meant that the distance continuously between the plates is approximately the same with a deviation of up to 10%.

In particular, the first plate may be substantially horizontal and slidably associated with a platform such that the rolling means comprises the first plate moving relative to a generally stationary second plate.

As the skilled person would appreciate, the components of the apparatus of the present invention may be made from any suitable material. For example, the first and second plates may be made from one or more materials selected from metal, glass, ceramic and/or plastics materials, such as polycarbonate.

Preferably, the first and second plates are each made from a material that is substantially hard and impermeable. It is preferred that the second plate also be made from a material that is substantially transparent or translucent. This enables the operator to view the sample during use of the apparatus. Thus, in one aspect, the first plate may be made from a metal (such as stainless steel) and the second plate may be made from a substantially transparent plastics material, such as polycarbonate and/or glass. For example, the second plate may comprise inclined glass plates fixed (for example by glue) to the underside of a polycarbonate plate.

As the skilled person would appreciate, the apparatus of the present invention may comprise any suitable measurement means for measuring the compression of the sample.

For example, the measurement means may comprise a gauge. In particular the gauge may be positioned so as to abut the second plate and measure compression of the sample indirectly. The gauge may, for example, comprise a depth or displacement gauge which measures the displacement of the second plate in contact with the sample, said ) displacement being caused by the decrease in width (or diameter) of the sample.

Alternatively, a linear variable displacement transducer could be used.

As the skilled person would appreciate, the apparatus of the present invention may comprise any suitable control means when such means is present. For example, the control means may comprise one or more objects moveable between different positions on the pressure means so as to exert a given (known) force at a given position to the sample.

The one or more objects moveable between different positions on the pressure means typically may each have a mass in the range of from 100 to 2500 g. As the skilled person would appreciate, the mass will be selected so as to exert a given range of forces at a given position to the sample and the particular mass selected will depend on the sample being tested. In one aspect, the mass of each particular object may be in the range of from 400 to 600 g, for example when it is desired to exert a relatively low force to the sample at a given position. Alternatively, when it is desired to exert a higher force to the sample at a given position, the mass of each object may be in the range of from 800 to 1000 g or in the range of from 1800 to 2200g.

As the skilled person would appreciate, the number of objects included in the control means and moveable between different positions may be selected according to the particular application and the substance being tested. For example, if it is desired to be able to exert a relatively low force (for example using an object of a weight in the range of from 400 to 600 g) then two objects may be included, whereas for a higher force (for example using an object of a weight in the range of from 800 to 1000 g or from 1800 to 2200 g) only one object may be used.

Alternatively, the control means may comprise a mechanical device operable to apply a force to the second plate so as to exert a given force at a given position to the sample. For example, a loading ram may be used. By "loading ram" is meant a device to apply a force to the second plate by mechanical means so as to exert a given force at a given position to the sample.

Suitable forces that may be applied to the sample are in the range of from 0 to 100 N, especially of from 0 to 20 N, even more especially of from 0 to 10 N. As a person skilled ) in the art would appreciate, the reference to a force of 0 N relates to the force applied to the sample at the start of the test, i.e. before the test is commenced. For the avoidance of any doubt, a Newton (N) is defined as the force required to accelerate a mass of 1kg to I rn/sec2.

In one aspect, the second plate and/or the first plate is configured so as to aid or allow the sample to spread laterally and/or longitudinally during rolling.

For example, the surface of the second plate and/or the first plate adjacent to the sample in use may be configured so as to form a U-shape, having a substantially flat horizontal strip at the location towards which the centre of the sample is located in use and inclined strips on each side of the central strip to allow the sample to spread laterally during rolling.

Preferably, the central strip of the U-shape configuration is substantially flat and horizontal and has a width in the range of from about 0.1 to 100mm (preferably in the range of from about 0.1 to 50 mm, more preferably in the range of from about 2 to 20 mm, even more preferably of about 10mm), with the sides being inclined at angles in the range of from about 0.1 to 15 (preferably in the range of from about 0.1 to 10 , more preferably of about 1.5 ) from the horizontal. Preferably, the inclined strips of the U-shape configuration have a width in the range of from about 5 to 150 mm, particularly of about mm. In one aspect, the flat strip of the U-shape configuration is positioned above or below the edges of the inclined strips, for example by a distance in the range of from about 0.1 to 20 mm, preferably of about 0.5 mm, from the edges of the inclined strips.

In another aspect, the surface of the second plate and/or the first plate adjacent to the sample in use may be configured so as to form a V-shape, with its apex towards the centre of the sample to allow the sample to spread or extrude laterally or longitudinally during rolling. Preferably, the inclined strips of the V-shape configuration may each have a width in the range of from about 5 to 150 mm, particularly of about 25 mm (for example to give a total width of 50 mm). Preferably, the inclined strips are configured at an angle in the range of from about 0.1 to 15 , particularly of from about I to 10 , more particularly of about 1.15 from the central point of the V-shape. )

in one aspect, the apparatus comprises start and finish locators so as to determine the known distance over which the sample is rolled. Any suitable known distance may be selected, for example a distance of from about 25 to 500 mm, particularly of from about to 500 mm, preferably of about 50mm. As the skilled person would appreciate, to move the thread over the known distance, of preferably about 50 mm, it is necessary to move the base plate by twice the known distance, i.e. preferably about 100 mm.

Therefore, the distance between the start and finish locators, when present and applied to the base plate, should be twice the known distance over which the sample is to be rolled.

The known distance is used to calculate the number of cycles of compression and tension applied to the substance (such as a soil sample) during a forward and backward traverse.

it is also intended to replicate the hand rolling procedure when the thread is rolled over a similar distance under the hand, of preferably 50 mm.

The known distance may, for example, be determined by a fixed stop at one end of the rolling traverse (such as a fixed stop block on the rolling means) and a moveable stop at the return end of the traverse (such as a rotating catch).

In one aspect, the apparatus is suitably sized and adapted to receive a generally cylindrical sample having a width in the range of from about ito 30 mm, preferably of about 8 mm, and a length in the range of from about 15 to 450 mm, preferably of about 60 mm.

In brief, in use, the apparatus of the present invention rolls a sample (such as a cylindrical sample or a thread) of a substance (such as soil) at a certain moisture content over a known distance under a known force and measures the compression of the sample, i.e. the change in diameter produced by the rolling and applied force. The moisture content of the sample is determined (for example using the procedure described in BS 1377:Part 2:1990) after the sample has been reduced to a diameter of 3 mm or less in its plastic condition.

Using this British Standard method, the moisture content is defined as the ratio of the weight of water in the substance to the weight of dry substance.

Typically, the test is commenced with the substance (such as soil) at a high moisture content above the plastic limit such that it is in a soft state but not sticky so that it will roll in the apparatus and not stick to the components of the apparatus. The test is repeated on ) separate samples of the substance at reducing moisture contents. The moisture content of the substance may be reduced by rolling and moulding the substance between the hands of the operator and, if necessary, by gentle blow drying ensuring that the substance is fully remoulded and homogenised before preparing a test sample.

For each sample at a given moisture content, the test is commenced by placing the prepared thread of a substance (such as soil) on the base, for example between the first and second plates, with zero force applied and the diameter of the thread is measured, for example indirectly by a gauge. The applied force is increased and the thread is rotated several times by rolling forwards and backwards over a known distance. The rolling typically is provided by one plate sliding relative to the other plate which is stationary.

The thread reduces in diameter and extrudes from between the two plates. The diameter of the thread is measured indirectly (for example by a gauge), the force is increased and rolling is repeated. Typically, the thread diameter is initially 8 mm, so that when it reaches a diameter of 6 mm sufficient stresses have been applied to reach the plastic condition and beyond the yield stress of the substance.

Tests carried out at moisture contents above the plastic limit are distinguished by longitudinal extrusion of the thread from between the two plates and reduction of the diameter to 3 mm or less. Tests carried out at moisture contents below the plastic limit are distinguished by the thread not reducing in diameter significantly, particularly not to 3 mm, and the thread generally breaking or fracturing as the substance is now in a brittle state. Thus the boundary or transition between plastic and brittle states can be clearly identified.

For each reading of known force applied and thread diameter, the work done per unit volume of the sample is calculated (by any suitable means). The work done may be calculated by multiplying the force applied by the change in diameter. The volume of the sample may be calculated from the sample dimensions and used to calculate the work done per unit volume. Alternatively, the work done may be calculated by multiplying the stress applied by the radial strain produced. The stress applied (or a quantity functionally related thereto) may be calculated by dividing the force applied by the value of the length multiplied by the diameter of the sample (i.e. force divided by [length x diameter]). The radial strain (or a quantity functionally related thereto) may be calculated by dividing the

II )

change in diameter by the initial diameter for each force increment. In calculating the stress andlor strain, allowance typically is made for variations in diameter along the length of the thread (for example if the thread assumes a conical configuration during testing).

Additionally, the number of cycles of rotation is calculated. The work and cumulative work done per unit of volume of the thread per set number (such as one hundred or ten, especially one hundred) cycles of rotation is plotted versus the diameter of the thread for each moisture content. The cumulative work done per unit of volume per set number (such as one hundred or ten, especially one hundred) cycles of rotation in reducing the sample diameter, preferably from 6 mm to 3 mm, is determined from this plot and is defined as the toughness of the substance at the particular moisture content.

A suitable set number of cycles of rotation may readily be determined by a person skilled in the art, for example as being suitable for the particular substance being tested, in the methods of the present invention. Any suitable set number of cycles of rotation may be selected, such as from 10 to 300, particularly from 10 to 150, more particularly from 10 to 100, for example 100. The set number of cycles of rotation ofcourse affects the toughness values determined by the method. For example, when the set number of cycles of rotation is 100, a typical range of toughness values is from 0 to 300 and when the set number of cycles of rotation is 10, a typical range of toughness values is from 0 to 30. The greater number of set number of cycles of rotation may be advantageous, as it provides a wider range of toughness values, which in turn allows for clearer distinction between different substances.

Values of the toughness of the substance at the particular moisture content are plotted against the moisture contents. From this plot the values of the toughness at the plastic limit (T), toughness coefficient (Ta), toughness limit (TL), hardening limit (HL), toughness index (TI) and toughness at the hardening limit TH can be determined, as discussed above.

The present invention also provides a method for the measurement of a plastic property of a substance, the method comprising the steps of: (a) receiving a sample of the substance; (b) applying a known force to the sample; (c) rolling the sample under the known force over a known distance; and ) (d) measuring the compression of the sample caused by rolling the sample under the known force over the known distance.

The apparatus and method of the present invention is advantageous because it provides a controlled rolling procedure, reduction of the thread diameter as required by the Standards, control of the force applied, measurement of the thread diameter and minimal operator interference with the substance (such as soil) during the test. The interpretation of the results does not rely on the operator's subjective impression of the crumbling condition.

As the skilled person would appreciate, the sample must be of a shape that is suitable for rolling across a surface or plate. For example, the sample may be a generally cylindrical shape (or thread).

In one aspect, the method of the present invention further includes the step of pre-forming the sample into a generally cylindrical shape (or thread). This may be accomplished using any suitable means or method, for example a suitable sizing tool may be used. In particular, the sample may be pre-formed so as to have a width (or diameter) in the range of from about 1 to 30 mm, preferably of about 8 mm, and a length in the range of from about 15 to 450 mm, preferably of about 60mm.

The known force may be applied to the sample at any suitable position of the sample.

When the sample is in a generally cylindrical form, the force typically is applied at a position axially along the whole length of the cylinder and diametrically along the axis of the cylinder.

The compression of the sample may be measured by any suitable means, i.e. by measuring any quantity functionally related to the compression of the sample. When the sample is in a generally cylindrical form, the compression typically is measured in terms of the decrease in a dimension, such as the width or diameter, of the cylinder. For the avoidance of any doubt, the compression is measured in step (d), after the sample has been rolled in step (c).

The present invention further provides a method for the measurement of the toughness of a substance, the method comprising the steps of: ) (a) receiving a sample of the substance; (b) applying a known force to the sample; (c) rolling the sample under the known force over a known distance; (d) measuring the compression of the sample caused by rolling the sample under the known force over the known distance by measuring the reduction in width or diameter of the sample; (e) repeating steps (b) to (d) under different known forces until the sample reaches a given compression (i.e. a given width or diameter), or alternatively until the sample crumbles; (f) determining the moisture content of the sample, or a quantity functionally related thereto, when it has been reduced to the given compression (i.e. the given width or diameter), or has crumbled; (g) calculating the work done per cubic unit of volume of the sample for each value of force and compression for a set number of cycles of rolling; (h) plotting the cumulative work done per cubic unit of volume of the sample per set number of cycles of rolling against the width or diameter of the sample; and (i) determining the cumulative work done per cubic unit of volume of the sample per set number of cycles of rolling in reducing the width or diameter of the sample from about 6 mm to 3 mm so as to provide the toughness (T) at the particular moisture content.

The present invention further provides a method for the measurement of the plastic limit of a substance, the method comprising the steps of: conducting steps (a) to (i) of the method above with a sample of a first moisture content, or a quantity functionally related thereto; (j) repeating steps (a) to (i) of the method above with a sample having a different moisture content, or a quantity functionally related thereto, to the first moisture content or quantity functionally related thereto; (k) plotting the values of toughness of the substance at the particular moisture contents (or quantities functionally related thereto) against the moisture contents (or quantities functionally related thereto); and (I) determining the plastic limit of the substance from the plot in step (k) as the moisture content at the transition from the plastic to the brittle states. )

The step (j) in the method above may be conducted a suitable number of times with samples of different moisture contents (or quantities functionally related thereto) as required to provide a suitable number of values for plotting in step (k) so as to enable the determination of the plastic limit in step (I).

The present invention further comprises a method for the measurement of one or more toughness properties of a substance, the method comprising the steps of: conducting steps (a) to (k) of the method above to provide a plot of toughness of the substance against moisture content (or quantity functionally related thereto); (m) determining the plastic limit of the substance according to step (I) above and determining as the toughness of the substance at the plastic limit; and/or (n) determining the Toughness Coefficient (Ta) of the substance as the gradient of the plot of toughness versus moisture content; and/or (o) determining the Toughness Limit (IL) as the moisture content at zero toughness; and/or (p) identifying the change in gradient of the plot of toughness against moisture content and determining the Hardening Limit (HL) as the moisture content at the break in the gradient; and/or (q) determining the toughness (T11) at the Hardening Limit; and/or (r) determining the toughness index (TI) as the difference between the toughness limit and the plastic limit.

In step (g) of the method of the present invention, the work done is calculated from the known force applied to the sample and the change in width or diameter of the sample for a set number of cycles of rolling for each forward and backward rolling traverse as discussed above. As the skilled person would appreciate, work may be calculated by multiplying a force (in Newtons) by a distance (in metres). Thus, the distance used in the calculation of work done is the change in width or diameter of the sample. Alternatively, the work done per unit volume may be calculated by multiplying the stress applied by the radial strain produced. Typically, the known force is in the range of from 0 to 100 N, particularly of from 0 to 20 N. Typically, the known distance over which the sample is rolled is in the range of from about 25 to 500 mm, particularly of from about 50 to 500 mm, preferably of about 50 mm. Is )

As discussed above, the method of the present invention may be used with any suitable substance, including soil.

According to another aspect of the present invention, there is provided a method for the measurement of a plastic property of a substance, using the apparatus as described herein.

According to another aspect of the present invention, there is provided the use of the apparatus as defined herein for the measurement of a plastic property of a substance.

Typically, the plastic property may be the plastic limit and/or the toughness of the substance. In one particular aspect, the substance is soil.

An apparatus for forming a sample into a generally cylindrical shape (or thread) of a predetermined size may comprise a tube for receiving the sample, pressure means for compacting and shaping the sample inside the tube and extraction means for extruding the sample from the tube.

Typically, the tube is dimensioned internally so as to correspond to the predetermined size of the cylinder or thread. In particular, the internal width or diameter of the tube is substantially constant and corresponds to the desired width or diameter of the cylinder or thread. A suitable internal width or diameter of the tube is from 8 to 10 mm, particularly 8 mm. The length of the tube typically is longer than the desired length of the cylinder or thread.

Typically, the tube comprises a hole or outlet at one or more locations (for example at one location) along its length, so as to allow for air to escape from the tube as the sample is compacted therein.

The apparatus for forming a sample into a generally cylindrical shape (or thread) preferably includes a stopper for insertion into one end of the tube and a rod having an external width or diameter of approximately the same size as the internal width or diameter of the tube. The stopper is preferably attached to a supporting block. The rod preferably carries a marking along its length that is equivalent to the desired length of the cylinder or thread. The tube and rod may be attached to gripping handles (such as rubber gripping handles) to aid in the use of the apparatus. )

In use of the apparatus for forming a sample into a generally cylindrical shape (or thread), a sample is formed into an approximately cylindrical shape by hand, which cylindrical shape is longer than the desired cylinder or thread and of about the desired width or diameter. The stopper is then inserted into a first end of the tube and the sample is inserted into a second opposite end of the tube, followed by the rod. The sample is compacted in the tube by pushing the rod onto the soil in the direction of the stopper until soil is extruded from the small hole. The rod is pushed into the tube until the marking on the rod coincides with the end of the tube. This ensures that the cylinder or thread of sample is of the desired length. As the rod is pushed into the tube, the user places one finger over the hole or inlet of the tube so as to allow air to escape but to minimise sample loss. Any surplus sample protruding from the tube is then removed and the resulting cylinder or thread of sample extruded from the tube. The cylinder or thread of sample prepared in this manner is suitable for use in the apparatus and method of the present invention for the measurement of a plastic property of the substance.

According to another aspect of the invention, there is provided a kit for the measurement of a plastic property of a substance (such as the plastic limit and/or the toughness), the kit comprising an apparatus for the measurement of a plastic property as described above and an apparatus for forming a sample into a generally cylindrical shape of a predetermined size as described above. Preferably the kit comprises instructions for use of the apparatus and for calculating the desired plastic properties of the substance.

The present invention will now be described by way of example only and with reference to the accompanying schematic drawings wherein: Figure 1 shows in cross-section, an apparatus for making a thread of soil.

Figure 2 shows in cross-section, the apparatus of the present invention for the measurement of a plastic property of a substance (such as soil).

Figure 3 shows in cross-section, the apparatus of the present invention with a thread placed at its initial position under a dial gauge.

Figure 4 shows in cross-section, the apparatus of the present invention at the location of a pivot support.

Figure 5 shows in cross-section, the apparatus of the present invention at the location of a rotating catch.

Figure 6 shows in long-section, the apparatus of the present invention with a metal rod placed on a base plate, before installation under a loading arm.

Figure 7 shows in long-section, the apparatus of the present invention with a metal rod at the starting position for rolling.

Figure 8 shows in long-section, the apparatus of the present invention with a thread after rolling forward.

Figure 9 shows in plan view, the apparatus of the present invention with a thread at the starting position for rolling.

Figure 10 shows in plan view, the apparatus of the present invention with a thread at the position after rolling forward.

Figure 11 is a plot of stress against cumulative strain as discussed in Example 1.

Figure 12 is a plot of cumulative work against thread diameter as discussed in Example 1.

Figure 13 is a plot of toughness against moisture content as discussed in Example 1.

Figure 14 is a plot of stress against cumulative strain as discussed in Example 2.

Figure 15 is a plot of cumulative work against thread diameter as discussed in Example 2.

Figure 16 is a plot of toughness against moisture content as discussed in Example 2.

Figure 17 is a plot of stress against cumulative strain as discussed in Example 3. )

Figure 18 is a plot of cumulative work against thread diameter as discussed in Example 3.

Figure 1 9 is a plot of toughness against moisture content as discussed in Example 3.

A sample of the substance, such as soil or clay, is prepared before it is placed on the apparatus of the present invention for testing.

Figure 1 shows an apparatus for making a thread of the substance, especially a thread having a consistent diameter (for example of 8 mm) and a consistent length (for example of 60 mm). The apparatus comprises a tube (1), for example having a length of 120 mm and an internal diameter of 8 mm. The tube (1) has a small diameter hole (2) (for example of a diameter of about 1 mm) drilled on one side. The apparatus further comprises a stopper (4), for example of a diameter of about 8 mm, attached to a support block (5). The apparatus further comprises a rod (6), for example of a diameter of about 8 mm. The rod (6) includes a marking (7) etched onto the rod (6) at a specified distance, for example a distance of 60 mm, from the end of the rod (6). Rubber gripping handles (3) and (8) are attached to the tube (1) and rod (6) respectively.

In use of the apparatus shown in Figure 1, an approximately circular cylindrical thread of soil is prepared by rolling gently by hand a lump of the soil on a flat smooth surface until the thread is of a diameter that will closely fit into the tube (1) and is longer than 60 mm.

The stopper (4) with attached support block (5) is placed into one end of the tube (I) and the soil thread is inserted into the tube (1) via, the opposite end of the tube (1) followed by the rod (6).

The soil is compacted in the tube (1) by gradually pushing the rod (6) onto the soil with the supporting block (5) placed on a firm surface. One finger is placed over the hole (2) to minimise the escape of soil but to allow the escape of air. The soil thread (23) is made to the required length, for example of 60 mm, by pushing the rod (6) into the tube (I) until the marking (7) coincides with the end of the tube (1), pushing out and removing the stopper (4). This ensures that the required length, for example 60 mm, of soil is inside the tube (I). The surplus soil protruding from the tube (1) is removed with a sharp knife and the end trimmed flat. The soil thread (23) is then extruded completely from the tube (1) ) and is pared from the rod (6) with the sharp knife. The thread (23) then is ready to use in the apparatus and method of the present invention.

As shown in Figures 2, 3 and 4, the apparatus of the present invention comprises a base section (10), which is made from a suitable material such as hardwood. The base section (10) supports a linear slide rail (11) or alternatively a linear roller bearing (not shown), which allows an attached plate (12), which may be a metal plate, to move linearly and horizontally along the base section (10). The plate (12) further includes a base plate or first plate (19), which may be made of metal. A glass plate (13) is attached to a polycarbonate plate (14) and both plates (13) and (14), together referred to as a second plate, are fixed in horizontal location and parallel to the line of traverse of the base plate (19) during the linear movement by a slot (15) in a vertical plate (16) which may be made of metal and is attached to the front of the base plate (19). Both plates (13, 14) of the second plate are free to rotate vertically on a pivot (29) as shown in Figure 4. In use, the soil thread (23) is placed at the front end of the base plate (19) of the apparatus adjacent to the vertical plate (16). A vertical plate (56) is located at the rear of the base plate (19) as shown in Figures 6 to 10.

In one aspect, the glass plate (13) is 150 mm long and U-shaped and comprises a central 10mm wide flat strip (17) with 20mm wide inclined strips (18) each side of the strip (17) and inclined upwards at an inclination of 0.5 mm in 20mm, or 1 in 40, or 1.43 away from the flat strip (17). The base plate (19) is 53mm long and has a central 10 mm wide flat strip (20) as well as 20mm wide inclined strips (21) each side of the strip (20). The edges of the inclined strips (21) are in contact with the central strip (20) and are raised above the central strip (20) by 0.5 mm and inclined downwards and away from the central strip (20) at an inclination of 0.5 mm in 20 mm, or 1 in 40, or 1.430. The overall width of the glass plate (13) arid the base plate (19) is 50 mm. This profile allows for holding the thread centrally in position between the glass plate (13) and the base plate (19) and for ready extrusion of the thread.

The apparatus further comprises a dial gauge (22) (typically a back plunger dial gauge) supported rigidly above the initial position of the soil thread (23) on the base plate (19) and centrally above the glass plate (13) and the polycarbonate plate (14) by a supporting arm (24) and dial gauge rod (26) fixed to the base section (10). Adjustable clamps (25) ) positioned on the supporting arm (24) and dial gauge rod (26) allow for small adjustments of the location of the dial gauge (22). The clamps (25) are tightened by a nut (27). The dial gauge (22) includes a spindle (28), which is in contact with the top of the polycarbonate plate (14) and is free to move vertically downwards as the diameter of the soil thread (23) reduces in use.

As shown in Figure 4, the apparatus of the present invention includes a pivot (29) supported on a pivot support plate (30). The polycarbonate plate (14) is fixed horizontally in both directions at this location by placing a V-shaped groove (31) located in the underside of the polycarbonate plate (14) above the pivot (29) and between small plates (32) attached to the pivot support plate (30). The polycarbonate plate (14) is then free to rotate vertically. The polycarbonate plate (14) can be removed for cleaning the surface of the glass plate (13). The polycarbonate plate (14) can be adjusted horizontally at the location of the pivot (29) by moving the pivot support plate (30) around slots (33) in the pivot support plate (30) and can be adjusted vertically by raising or lowering lower nuts (34) supporting the pivot support plate (30) and attached to threaded supports (35) which are fixed to the base section (10). Once adjusted, the pivot support plate (30) is clamped in place by upper nuts (36).

As shown in Figure 5, the apparatus of the present invention includes a rotating catch (37) which comprises a metal strip attached to a support bracket (38) by a pivot bolt (39) so that the rotating catch (37) can rotate around the bolt (39) by means of the handle (40). In use, the rotating catch (37) is lowered to allow the metal plate (12) to be moved from beneath the glass plate (13) and the polycarbonate plate (14) and raised to provide a stopblock for the metal plate (12) when the soil thread (23) is returned to its initial position at the end of the backward rolling traverse. The apparatus further includes a stopblock (55) at the end of the forward traverse.

In use, the polycarbonate plate (14) is removed from the apparatus and the glass plate (13) is cleaned, dried and greased. A very thin film of petroleum jelly typically is smeared on the strips (18) at the sides of the glass plate (13) to provide a smooth surface for extrusion of the soil thread (23) during rolling. The surface of the base plate (19) is cleaned and dried but not greased. The polycarbonate plate (14) is placed on the apparatus with its V-shaped groove (31) placed on the pivot (29) and with the base plate (19) moved with a ) hand'e (48) in the direction of the arrow (49) shown in Figure 6. With the rotating catch (37) lowered, the other end of the polycarbonate plate (14) is lowered to rest on the plate (12).

As shown in Figure 6, a weight (41) is attached to one end of the polycarbonate plate (14) with a threaded rod (42) drilled and glued inside the end of the polycarbonate plate (14) and fixed with a wing nut (43). Referring to Figure 7, a moveable weight (44) also is placed on the polycarbonate plate (14), with a marking (45) provided at the centre of gravity of the moveable weight (44). The moveable weight (44) rests on the top of the polycarbonate plate (14) and is moved along a guide (46). Markings (47) are provided on a side of the polycarbonate plate (14) to denote the average force applied to the soil thread (23) (in Newtons) when the marking (45) on the moveable weight (44) is placed at these markings (47). The moveable weight (44) can be placed manually with the markings (45) and (47) coincident to give a known average force applied to the soil thread (23).

Depending on the toughness of the soil tested, there are different weights (41) and moveable weights (44) associated with different scales of force markings (47), so that the range of forces applied to the soil thread (23) can be changed to suit the particular substance being tested.

To calibrate the measurement of the compression of the thread (23), a metal rod (50) of 3 mm width or diameter is placed at the front of the base plate (19) adjacent to the vertical plate (16) and at a marking (51).

As shown in Figure 7, with the moveable weight (44) at the zero force marking (53) the end of the polycarbonate plate (14) beneath the dial gauge is raised to allow the base plate (19) to be moved with the handle (48) in the opposite direction to the arrow (49) until the rotating catch (37) can be raised and become a stopblock at the rear of the plate (12). The polycarbonate plate (14) and the attached glass plate (13) are lowered and placed onto the metal rod (50) at the marking (52) on the polycarbonate plate (14) so that markings (51) and (52) then coincide vertically. The rotating catch (37) is kept raised.

The apparatus is adjusted by lifting or lowering the base section (10) until the metal plate (12) is horizontal in both directions by placing a spirit level on the surface of plate (12).

With the 3 mm diameter metal rod (50) inserted between the glass plate (13) and the front of the base plate (19) at the marking (51), the pivot (29) is then raised or lowered as necessary by adjusting the locations of the lower nuts (34) until the top of the polycarbonate plate (14) is horizontal in both directions by placing a spirit level on the surface of the polycarbonate plate (14). If necessary, the pivot (29) is also moved horizontally by means of adjustment around the slots (33) in the pivot support plate (30) to ensure that the centre line of the polycarbonate plate (14) and the glass plate (13) are coincident with the line of travel of the base plate (19) during rolling of the thread (23) and the marks (51) and (52) are coincident vertically at the commencement of rolling. The check and any necessary adjustment for level should be carried out at the start of a test on each different substance.

As shown in Figure 7, the moveable weight (44) is placed initially at the zero force marking (53) to give zero force on the metal rod (50). The reading on the dial gauge (22) is taken by allowing the spindle (28) to contact the top of the polycarbonate plate (14) and is recorded as the dial gauge reading at the diameter of 3 mm. The diameter of the thread (23) and its changes during the test can then be determined from the subsequent dial gauge readings. The dial gauge reading at the diameter of 3 mm is determined for each thread (23) at each moisture content to ensure that the readings are initialised and the dial gauge has not moved. The end of the polycarbonate plate (14) beneath the dial gauge is lifted, the rotating catch (37) is lowered, the base plate (19) is retracted by moving the handle (48) in the direction of the arrow (49), the metal rod (50) is removed and the polycarbonate plate (14) is lowered to rest on the plate (12).

The soil thread (23) is extruded from the tube (1) and placed at the front of the base plate (19) at the marking (51). The polycarbonate plate (14) then is raised, the base plate (19) is moved in the opposite direction of the arrow (49) until the rotating catch (37) can be raised and the polycarbonate plate (14) and the attached glass plate (13) is lowered and placed gently onto the thread (23). The initial reading on the dial gauge (22) is taken as the reading to give the diameter of the thread (23) at zero force.

As shown in Figures 7 and 8, with the thread (23) at its initial position, the moveable weight (44) is placed at a marking (47) to apply an appropriate force to the thread (23) and the base plate (19) is moved by the operator using the handle (48) in the direction of the arrow (54) until it is prevented from further movement in this direction by a stopblock (55). As the base plate (19) is moved forward, the thread (23) will have rolled and moved horizontally to the rear of the base plate (19). The base plate (19) is then immediately returned to its initial position when the metal plate (12) is in contact with the raised rotating catch (37) and with the thread (23) returned to the front of the base plate (19) at marking (51). The dial gauge reading is recorded to give the diameter of the thread (23) and the force applied is recorded. The force on the thread (23) is changed by moving the moveable weight (44) to another marking (47) and the rolling procedure repeated. As the skilled person would appreciate, the magnitude of the force applied to the thread (23) and the increments of additional force applied depend on the soil type and mainly its toughness. Initially, the force typically is increased gradually with increments applied to achieve changes in diameter of from 0.1 to 0.2 mm. For some soil types and moisture conditions, the force applied may be held constant to achieve the required changes in diameter and may even be reduced considering that for a given force the stress on the soil thread (23) increases as its diameter decreases and after a certain amount of stress has been applied only small increments of further stress should be applied. The forward and backward rolling comprising one traverse should be conducted at a speed such that the traverse is completed within about 3 seconds. The forward and backward rolling process is repeated and the dial gauge reading and force applied are recorded after each traverse.

With the moisture content of the substance of the thread (23) above the plastic limit during rolling, the thread (23) extrudes longitudinally out from between the glass plate (13) and the base plate (19) and is retained on the metal plate (12) if it breaks away. Rolling is continued until the diameter of the thread (23) is reduced to 3 mm or less. If the substanceof the thread (23) is at a moisture content below its plastic limit, the thread (23) will not be extruded readily and the thread may crumble or split.

At the end of the test, the thread (23) is removed by lifting the glass plate (13) and retracting the base plate (19) with the rotating catch (37) lowered. The thread (23) and pieces of the thread are collected and placed in a container for immediate weighing to determine its moisture content according to the oven-drying procedure in British Standard BS I 377:Part 2:1990. The thread should be handled as little as possible to avoid drying out.

The test for each substance (for example soil sample) preferably is commenced with the substance in its softest condition (for soil at its wettest) to give its lowest measurable toughness but such that it produces satisfactory rolling and extrusion between the plates and does not stick to the glass plate (13) andlor the base plate (19). These threads are at moisture contents above the plastic limit. After the first thread has been rolled, another thread of the prepared substance is made at a slightly reduced moisture content and the test repeated.

The procedure is continued by reducing the moisture content of the substance until it is not possible to extrude the thread (23) between the glass plate (13) and the base plate (19) and the thread (23) either collapses or fractures usually before reaching the diameter of 3 mm.

The moisture content is then below the plastic limit and the test is completed. Comments are recorded about the quality of the extrusion process for threads with moisture content above the plastic limit and the condition of the thread and nature of its failure for threads with moisture content below the plastic limit.

From the dial gauge readings and the initial reading with the 3 mm diameter metal rod (50), the diameter of the thread (23) after each traverse is determined. As the thread (23) rotates, the load applied changes the pressure on the thread from compression to tension and the number of cycles of compression/tension is determined from the average diameter of the thread for each traverse and the length of travel during rolling. The pressure or stress on the thread is determined as the ratio of the force applied (in Newtons) divided by the measured diameter and the length of the thread (23) between the glass plate (13) and the base plate (19) of 50 mm. The radial strain after each traverse is determined as the ratio of the change in diameter and the initial diameter at the start of each traverse. The work done per unit volume per set number, for example one hundred, cycles of compression/tension is computed as stress multiplied by radial strain divided by the number of cycles multiplied by 100. For each thread the cumulative values of work are plotted on a graph on a natural scale versus the thread diameter on a natural scale. The total amount of work done to change the diameter of the thread from 6 mm to 3 mm is then determined from the graph and is defined as the toughness of the soil at the moisture content of the thread. These toughness values are plotted versus moisture content, both at natural scales. The best fit lines are drawn through the points bearing in mind that a break in the slope is often observed at the moisture content defined as the Hardening Limit with different gradients each side of this moisture content. At least four points should be

I

obtained each side of the Hardening Limit to be able to define reasonable lines each side of this break in slope.

The transition from the plastic condition to the brittle condition is detected by a marked reduction in the toughness of the thread (23) when it breaks or fractures and that the thread will not reduce in diameter to a diameter of 3 mm. This transition occurs at a certain moisture content defined as the plastic limit. Providing there are test results for two threads with moisture contents each side of the plastic/brittle transition and within 1/40 of their average value, the plastic limit is determined as the average moisture content of these two results.

Hardening Limit (HL) is defined as the moisture content at which the gradient of the plot of toughness versus moisture content changes and is typically where the substance alters from a mainly strain hardening material to a mainly strain softening material. is determined from the best fit line of toughness versus moisture content below the Hardening Limit, as the value of toughness of the substance when at the plastic limit.

Thus this is the maximum amount of work that can be applied while the soil is still plastic.

Toughness Coefficient (Ta) is defined as the rate of change of toughness per unit change of moisture content and is determined for the different gradients both above and below the Hardening Limit. Toughness Limit (TL) is defined as the moisture content at which the toughness of the substance is zero and is obtained by extrapolating the plot for moisture contents above the Hardening Limit (HL). Toughness Index (TI) is defined as the difference between the Toughness Limit and the Plastic Limit. TH is defined as the value of toughness at the Hardening Limit.

The invention will now be illustrated by the following non-limiting Examples. The Examples were chosen to represent a range of toughnesses, such as those likely to be encountered with a sample of reworked chalk providing toughness at the low end of the range, a sample of Wyoming Bentonite providing very high toughness and a sample of Broadstone Clay providing an intermediate toughness.

Example I

(i) Material For this example a test was carried out on a sample of Broadstone Clay. Geologically Broadstone Clay is a clay deposit within the Poole Formation of the Lower Eocene. A sample of the untreated, unprocessed clay was obtained from the Imerys Minerals Ltd pit at Povington, Dorset (UK) where it is referred to as Povington GP clay. This clay is a high strength plastic ball' clay used in the ceramics industry and is processed for the production of electrical porcelain, tiles and tableware.

(ii) Soil Preparation To a finely pulverised sample of the clay water was added to make a paste of a soft consistency but not sticky to the touch. The paste was then moulded by hand several times into a ball and then a thread to achieve a homogeneous mass. The soil was at its highest moisture content for the test and could be rolled between the plates without sticking to them.

(iii) Thread Preparation The thread was prepared using the apparatus for preparing a thread as described above. A small piece of the prepared soil was rolled by hand on a flat surface to a near uniform diameter ofjust less than 8mm. The soil was inserted into the apparatus and squeezed to fill the tube diameter with the stopper and the rod inserted in the tube. Air was expelled via, the small hole in the side of the tube. The rod was pushed to the mark at which point there was 60 mm length of soil thread inside the tube. The end of the thread was trimmed with a knife. When the apparatus was ready, the soil thread was pushed out of the tube and placed at the starting point on the base plate of the apparatus.

(iv) Apparatus Setup The moveable weight was placed at the mark on the top plate to give zero force at the starting point location. With the 3 mm diameter metal rod placed at the starting point the dial gauge reading R3.0 was taken, which for Test No I of Example I was R3.0 = 0.15 mm.

The diameter of the soil thread was determined for each subsequent dial gauge reading from this value.

With the metal rod in place the base plate was checked for level in both horizontal directions by placing a small spirit level on the lower plate. The apparatus was lifted or lowered bodily to adjust for level. The top plate was then checked for level in both directions with the spirit level and any adjustments were made at the pivot end of the top plate by moving the nuts as necessary up or down. In this way the base plate and the top plate are both in horizontal planes and parallel when the thread diameter is 3.0 mm. When the soil thread is in place the top plate is slightly angled from the base plate and this is considered to apply some slight horizontal force component to the thread which assists extrusion.

(v) Test Procedure (Test No 1) The metal rod was removed and the soil thread extruded from the tube and placed on the base plate at the starting point. The dial gauge reading was taken which for Test No I was 5.00 mm. This means that the diameter at this point was 3.0 -0.15 + 5.00 = 7.85 mm. To impress the soil thread into the shape of the top and bottom plates a force was applied, in this case 0.4 N, by placing the moveable weight at the appropriate mark. As soon as the force was changed, the base plate was moved forward and backward to roll the thread.

With the thread returned to the starting point the dial gauge reading was taken, in this case 4.73 mm. Now the diameter was 3.0 -0.15 + 4.73 = 7.58 mm.

A moderate impression had been made on the thread, so the force was increased by an increment of 0.2N to 0.6N and the thread was rolled again and the dial gauge reading taken as 4.46 mm. As a large impression had been made on the thread a smaller increment of 0.lN was applied to 0.7N and the thread was rolled again. It is to be noted that for a constant force the stress applied to the thread increases as the diameter decreases. For the next few increments of force the thread was rolled for two traverses at each force. The sample was rolled for two traverses or, if necessary, more at the same force to determine whether the soil was strain softening or strain hardening. In Test No 1 the soil was strain hardening so to achieve further strain the force had to be increased. Further traverses were carried out until a maximum force of 1.4 N was applied. At this stage changes in diameter of between 0.10 and 0.20mm were recorded so it was considered that the stresses applied were close to the soil's failure strength and continued rolling traverses were undertaken at this force, knowing that nevertheless the stresses were increasing.

Later, when the changes in diameter approached 0.2 mm the force on the thread was reduced to 1.3 N and rolling was continued. Further reduction of force was required to keep the changes in diameter within the required range. It was found that with changes in diameter less than about 0.1 mm too many traverses were required to complete the test while with changes in diameter greater than about 0.2mm there was a risk of collapse of the thread across the diameter and premature termination of the test instead of longitudinal extrusion of the thread which is the purpose of the test. When the dial gauge reading reached the R3.0 reading the test was discontinued soon after. Test No I was complete after 41 traverses. it is preferred that the reduction in thread diameter is achieved by about to 40 traverses.

At the end of Test No 1, the pieces of soil thread were collected together and without delay were placed in a pre-weighed tin. For Test No 1 the tin number was 6 and its weight was 0.590 g. The tin + wet weight of soil was 5.709 g. The tin was placed in an oven and set at 105 C for 24 hours to obtain its dry weight according to the BS 1377:1990 oven-drying method for moisture content. The following day the tin was removed and weighed to give the tin + dry weight as 4.052 g. The moisture content, in terms of dry weight, was determined as: 5.709 -4.052 (weight water) x 100 = 47.86% 4.052 -0.590 (weight dry soil) (vi) Subsequent Tests For Test No 2 and subsequent tests the prepared soil was moulded in the hands to reduce its moisture content slightly. Although not always necessary, blow drying may be applied especially for some higher plasticity clays. A thread was made as before, the R30 reading was taken and the test repeated. Due to its lower moisture content the soil was tougher and stronger so higher forces needed to be applied.

The state of extrusion of the thread was noted in terms of its rolling performance such as uniformity, equal both sides, sticking to the plates or not. For Test No I the thread was sticking slightly to the base plate and did not roll entirely as required. The result of this test may, if necessary, be excluded from the assessment of the toughness properties on the graph of work versus moisture content. For Test Numbers 2 to 15 the threads rolled as required and were marked as Exc' to denote that the required rolling and extrusion process had been achieved.

The essence of the test is to apply stresses and produce strain and hence mimic a stress-strain curve. The stress-strain curves for each Test are plotted on Figure II (from the data determined as described below in relation to Table 2). To achieve a reasonable rate of strain applied to the thread it is considered preferable to reduce the diameter by between 0.1 and 0.2 mm for each rolling traverse so values of force are chosen accordingly. The rate of application of force for the first test was tentative because it was not known how tough the soil would be. For subsequent tests the rate of application of force could be judged by reference to the previous test which would have been somewhat weaker so slightly higher forces needed to be applied.

If the stress applied approached the failure strength of the soil while the soil was still in a plastic condition then instead of extrusion the thread would collapse and squash across its diameter. This would mean the premature end of the test. This occurred for Test 12 because the forces were applied too confidently. This can be seen in Figure 11.

The data from Test Nos 1 to 15 is presented below in Table 1: t =I C) Ei5

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-. -5-5 Cj.3U1.O

Table I Continued

TestNo. 13 14 15 16 17 18 Tin Number 49 39 29 ____________ Tin weight 0.603 0.596 0.595 ____________ Tin + wet weight 5.974 -6.022 6.024 ____________ Tin + dry weight 4.426 4.465_.... 4.478 ____________ Moisture content % 40.49 40.24 39.81 ____________ 0.16 017 -0.17 _____ _____ _____ _____ _____ _____ Dial Dial Dial Dial Dial Dial Force gauge Force gauge Force gauge Force gauge Foe gauge Force gauge mm mm mm mm mm mm o 199 () 5.01 0 5.02 - 0.8 io 0.8 4.92 1.0 4.84 ______ 1.0 4.83_ 1.0 4.83 1.4 4.70 _____ 1.2 4.7S 1.2 4.76 1.8 4.54 ______ 1.4 4.67 1.4 -4.68 2.2 4.38 ______ 1.6 4.58 1.6 460 2.4 4.30 _____ 1.8 4.51_ 1.8 52 2.6 4.21 _____ 2.0 4.42 2.0 449 2.8 4.12 ______ 2.1 4.34 2.2 4.37 2.9 4.02 ______ 2.2 4.29 2.4 4.29 3.0 3.94 ______ 2.3 422 2.5 4.21 3.1 6 ______ 2.4 i6 2.6 4.15 32 3. 78 ______ 408 2.7 4.07 3.2 3.71 ______ 2.8 399 2.8 4.00 3.3 3.63 ______ 2.7 3.89_ 2.9 3.91 3.3 3.55 ______ 2.7 3.81 3.__ 3.82 3.4 3.47 ______ 2.8 3. 74 3.0 3.74 3.4 3.37 ______ 2.8 3.64 3.1 3.64 3.4 3.29 ______ 2.9 3.55 3.1 3.56 3.4 3.21 ______ 29 3.47 3.2 3.48 3.4 3.13 ______ 3.0 3.35 3.2 3.38 3.4 3.03 ______ 3.0 27 3.3 3.28 3.4 2.92 ______ 3.1 3.15 3.3 3.19 3.4 2. 85 _____ 3.1 3.05_ 3.4 3.10 3.4 2.80 ______ 3.2 i5 3.4 299 3.4 2.77 ______ 3.2 2.84 3.5 2.88 3.4 2.70 _____ 3.3 2.73 ______ ______ 3.3 2.60 ______ ______ 3.3 2.45 ______ ______ 3.3 2.35 ______ 3.3 2.19 ______ ______ 3.3 2.06 -______ ______ 3.3 1.91 _____ _____ 3.3 1.74 ______ 3.2 1.57 ______ ______ 3.0 1.44 _____ _____ 3.0 1.27 ______ ______ 2.8 1.12 ______ ______ 2.8 0.93 ______ ______ 2.6 0.82 ______ ______ 2.6 0.64 ______ 2.4 0.57 _____ _____ 2.4 0.43 ______ ______ 2.2 0.34 ______ ______ 2.2 0.21 ______ 2.1 0.13 ______ _______

_

xc Exc xc squashedlsplit squashed/Split Comments (vii) Calculating Results From the values of force and diameter the amount of work done per unit volume was calculated using stress x strain for each increment of force. The units of work are kJ/m3.

As the thread reduced in diameter the number of cycles or revolutions increased during the rolling traverses. This means that the number of reversals of stress from compression to tension across the diameter of the thread was increasing. To include this effect the work per unit of volume per 100 cycles was calculated. The cumulative values were then determined by summation. An example of the results from a spreadsheet analysis of Test Nos 1 and 2 is presented below as Table 2. The input data is inserted in the first two columns on the left hand side of each Test block (i.e. the force values applied by the operator during the test, chosen to give dial gauge readings preferably between 0.1 and 0.2mm and the dial gauge readings taken following the forward and backward traverse under each force value) and the calculations follow to the right. These calculations are for the final diameter (calculated from the dial gauge reading minus the R3.0 reading plus 3.00 mm), average stress (calculated from the force divided by the length and the diameter, allowing for the varying diameter along the length of the sample), average strain per increment (calculated from the change in diameter divided by the original diameter, allowing for the varying diameter along the length of the sample), cumulative strain (the summation of the strain per increment in the previous column), Wd per 100 cycles (calculated from the average stress multiplied by the average strain divided by the number of cycles of compression/tension multiplied by 100, allowing for the varying diameter along the length of the sample) and cumulative Wd (the summation of the increment of work in the previous column). Whilst Table 2 shows the calculation results for tests I and 2 only, these were calculated for the remaining tests in the same way and the results plotted in the graphs discussed herein.

Table 2

Test Number 1 1 1 1 1 j TeSt Number 2 2 2 2 2 2 Force j F*rial AVE Ave CUM CUM Force Final AVE Ave CUM 6Wd CUM N giuge 0mm Stress Strain. per 100 gauge Utam Stress Strato per 100 5W nan mm kN/m2 per inc. $ tO mm mm KN/m2 per nc. itdes o 5.00 0 4.67 0.4 4.73 0.4 4.62 0.6 4.46 7.31 0.9455 0.0335 0.0335 0.7408 0.7408 0.6 4.44 7.28 0.9597 0.0227 0.0227 0.5044 0.5044 0.7 4.35 7.21 1.1412 0.0128 0.0463 0.3332 1.074 0.7 4.32 7.16 1.1456 0.0155 0.0382 0.4028 0.9072 0.8 4.24 7.09 1.3211 0.0156 0. 0619 0.4629 1.5369 0.8 4.21 7.05 1.3298 0.0144 0.0526 0.4274 1.3346 0.8 4.18 7.03 1.342 0.007 0.0698 0.235 1.772 0.9 4.07 6.91 1.5178 0.0186 0.0712 0.6191 1.9537 0.9 4.08 6.93 1.5218 0.013 0.083 0.4438 22158 1.0 3.93 6.77 1.7183 0.019 0.0902 0.7015 2.6552 0.9 4.00 6.85 1.5423 0.010 0.0939 0. 3805 2.576 1.0 3.85 6.69 1.7514 0.011 0.1012 0.4073 3.0625 1.0 3.93 6.78 1.73 0.009 0.1035 0.356 2.9323 1.1 3.71 6.55 1.9479 0.0195 0.1207 0.79 3.8525 1.0 3.85 6.7 1.749 0.01 0.1145 0.4074 3.339 1.1 3.60 6.44 1.9866 0.0157 0.1364 0.6364 4.4889 1.1 3.74 6.59 1.9452 0.0153 0.1298 0.6213 3.961 1.2 3.47 6.31 2.2016 0.0188 0.1552 0.8289 5.3178 1.1 3.64 6.49 1.9754 0.0142 0.144 0.57 4.537 1.2 3.37 621 2.2436 0:0147 0.1699 0.6486 5.9664 1.2 3.52 6.37 2.1858 0.0172 0.1612 0.75 5.2968 1.3 3.20 6.04 2.4668 0.0254 0.1953 1.2057 7.1721 1.2 3.43 6.28 2.224 0.0132 0.1744 0.58 3 5.880 1.3 3.08 5. 92 2.5309 0.0184 0.2137 0.8749 8.047 1.3 3.29 6.14 2.4413 0.0207 0.1951 0.9859 6.866 1.4 2.93 5.77 2.7765 0.0235 0.2372 1.1981 92451 1.3 3.15 6 2.4928 0.0212 0.2163 1.0078 7.8738 1.4 2.80 5.64 2.843 0.0208 0.258 1. 0599 10.305 1.3 3.05 5.9 2.5465 0.0155 0.2318 0.7 7 8.6116 1.4 2.65 5.49 2. 9032 0.0246 0.2826 1.2486 11.554 1.4 2.90 5.75 2.7852 0.0236 0.2554 1.2 9.814. 4 2.50 5.34 2.9759 0.0252 0.307 1.2758 12.829 1.4 2.76 5.61 2.8521 0,0225 0.2779 1.1451 ID.4 2.37 5.21 3.0523 0.0224 0.3302 1 13.962 1.4 2.63 5.48 2.9174 0.0214 0.2993 1.0876 12. 7.4 2.19 5.03 3.1218 0.0317 0.361 1. 15.554 1.4 2.49 5.34 2,9808 0.0235 0.3228 1.1906 13. 1.4 2.01 4.85 3.2234 0.0328 0.394 1. 17.1 1.4 2.34 5.19 3.0523 0.0258 0.3486 1.3026 14.54 1.3 1.83 4.67 3.0939 0.0339 0.4286 1.5884 18.76 1.4 2.15 5 3.1328 0.0336 0.3822 1.6849 16.225 1.2 1.72 4.56 2.9553 0.0214 0.45 0.916 19.6 1.3 2.03 4.88 3.0095 0.022 0.4042 1.0275 17253 1.2 1.44 4.28 3.0195 0.0558 0.5058 2.33 22.0 1.3 1.68 4.73 3.0766 0.0281 0.4323 1.305 18.558.1 1.34 4.18 2. 93 0.021 0.5269 0. 22.84 1.2 1.81 4.66 2.9214 0.0135 0.4458 0.5817 19.14.1 1.14 3.98 2.9927 0.043 0.57 1. 24.49 1.2 1.59 4.44 2.961 0.043 0.4888 1. 82 20.96..0 1.04 3.88 2.8421 0.0225 0.5925 0. 25.284 1.0 1.50 4.35 2.5774 0.0184 0.5072 0.6548 21.614 1.0 1.02 3.86 2.9069 0.0046 0.5971 0.1 25.44 1.0 1.41 4.26 2.6252 0.0187 0.5259 0.6639 22278 1.0 0.80 3.64 2.9203 0. 051 0.6481 1.7546 27.202 1.0 1.35 4.2 2.6749 0.0127 0.5386 0.4514 22.73 0.9 0.65 3.49 2.7679 0.0367 0.6848 1.1377 28.339 1.0 1.21 4.06. 2.709 0.0301 0.568 1.058 23.788 0.8 0.57 3.41 2.5529 0.0203 0.7051 0.561 28.901 1.0 1.05 3.9 2.7922 0.0354 0.604 1.2359 25.024 0.8 0.43 3.27 2.6051 0.0363 0.7414 0.992 29.893 1.0 0.90 3.75 2.8937 0.0344 0.6385 1.1962 26.22 0.7 0.29 3.13 2.3841 0.0377 0.7791 0.896 30.769 0.9 0.84 3.69 2.6963 0.0143 0.6528 0.4506 26.67 0.6 025 3.09 2.1045 0.0112 0.7903 0.230 31.02 0.9 0. 70 3.55 2.7349 0.0338 0.6866 1.05.13 27.722 0.6 0.18 3.02 2.128 0.0198 0. 8101 0.4044 31.424 0.9 0.65 3.5 2.8294 0.0125 0.699 0.3917 28.113 0.6 0.16 3 2.1703 0.0068 0.8159 0.119 31.543 0.9 0.59 3.44 2.8648 0.0152 0.7143 0.4747 28.588 0.6 0.12 2.96 2.1827 0.0116 0.8275 0.237 31.78 0.9 0.50 3. 35 2.9084 0.0231 0.7374 0.7166 29.305 0.9 0.44 3.29 2.9764 0.01 58 0.7532 0.4905 29.795 0.9 0.39 3.24 3.0235 0.0134 0.7666 0.4156 30211 0.9 0.18 3.03 3.0639 0.057 0.8236 1.72 31.931 - 0.9 0.04 2.89 3.2462 0.0403 0.8639 1.2165 33.147 Test No I R30 0.15mm Test No 2 R10 = 0.16mm (viii) Plotting Results The cumulative work values were plotted versus diameter for each test. This plot is shown in Figure 12. From this plot for each test the cumulative work done is determined between the diameters of 6 mm and 3 mm. In other words, this is the work done to change the diameter of the thread from 6 mm to 3mm and is referred to herein as toughness, T. This is the same procedure as in the BS test for plastic limit but with measurements of force and displacement.

For each test the value of toughness (or work) was plotted versus the moisture content.

This plot for Example 1 is shown in Figure 13. From this plot the various properties of the soil can be determined, for example the plastic limit. Test 13 was on the plastic side and Test 14 was on the brittle side of the plastic-brittle transition. In Test 13 the soil extruded to 3 mm diameter whereas in Test 14 the thread split and fractured before reaching 3 mm diameter. The respective moisture contents as determined for dry weights by the BS1377:1990 method were 40.49% and 40.24%. The plastic limit is taken as the mean of these results, i.e. 40.37%. The two moisture contents are within 1/40 of their mean value so this is considered a valid result. For the BS test the plastic limit is required to be stated to the nearest whole number, in this case 40%.

Best fit lines were drawn through the plot shown in Figure 13 above and below the Hardening Limit (HL). The Hardening Limit is taken as the moisture content when the soil changes from a mainly strain hardening material with higher moisture contents to a mainly strain softening material at the lower moisture contents. This change can be detected on the plot of stressversus strain for each test, given in Figure 11. This is a useful transition when assessing the behaviour of the soil at different moisture contents.

(ix) Properties The Toughness Coefficient is the gradient of the toughness versus moisture content plot and is determined for the lines both above and below the Hardening Limit. A value for the Hardening Limit of 43.3% was obtained from Figure 13. For the upper limb the Toughness Coefficient is 8.04. From this Coefficient for the upper limb the value of the toughness at the plastic limit is determined. Alternatively the value can be scaled from the plot in Figure 13. A value of 64 kJ/m3 was obtained.

For the lower limb the Toughness Coefficient is 3.89. From the Toughness Coefficient for the lower limb the value of T0 is determined, the moisture content at zero toughness, the Toughness Limit. Alternatively the value can be scaled from the plot in Figure 13. A value of 54% was obtained.

It is not possible to test the soil near to the value of T0 as it is in a very soft condition and in particular it is sticky and will stick to the plates of the apparatus preventing a meaningful test. There is a property referred to as the Sticky Limit, the moisture content above which the soil is sticky. This test is rarely used and has no standardised procedure.

Example 2

(i) Material For this example a test was carried out on a sample of Reworked Chalk. This soil was obtained from a site in Chinnor, Oxfordshire (UK). It comprises chalk that has been naturally mechanically weathered and highly disintegrated due to periglacial action and may include some solifluction debris. It is sometimes referred to as putty chalk'. The soil is unsuitable for use as a fill material and has low ground bearing pressures due to its inherent weakness.

(ii) Soil Preparation To a sample of the naturally occurring soil water was added to make a paste of a soft consistency but not sticky to the touch. The remainder of the soil preparation was carried out as described for Example 1.

(iii) Test Procedure The thread preparation, apparatus setup and test procedure was earned out in the same way as for Example I. ) (iv) Results The results of the tests were calculated and plotted in the same manner as for Example 1.

(v) Properties The plots of stress versus strain are presented in Figure 14. The plots of work per unit volume versus diameter are presented in Figure 15. The plots of work per unit volume versus moisture content are presented in Figure 16. A value for the Hardening Limit of 26% was obtained from Figure 16. For the upper limb the Toughness Coefficient is 7.67.

Frorri this Coefficient for the upper limb the value of the toughness at the plastic limit is determined. Alternatively the value can be scaled from the plot in Figure 16. A value of 29 kJ/m3 was obtained.

For the lower limb the Toughness Coefficient is 3.83. From the Toughness Coefficient for the lower limb the value ofTo is determined, the moisture content at zero toughness, the Toughness Limit. Alternatively the value can be scaled from the plot in Figure 16. A value of 30.4% was obtained.

Example 3

(i) Material For this example a test was carried out on a sample of natural Wyoming Bentonite. This material is a naturally occurring mineral sodium montmorillonite which is imported from the United States and supplied by Voiclay Ltd, Birkenhead, Merseyside (UK). In its pure form it has a range of uses from a binding agent, pelletising agent, filler in pharmaceuticals, cosmetics, paints, paper and in the construction industry it is used as a drilling fluid, grouting medium and in tunnelling and diaphragm walling installation. It is a highly colloidal mineral and istypically the most plastic natural clay mineral in the world and would be expected to provide the highest values of toughness. It provides a constituent in many natural soils where it is found mixed with other earth minerals.

(ii) Soil Preparation ) To a sample of about 200 grams of the powder (as supplied) water (about 200 grams) was added to make a paste of a soft consistency but not sticky to the touch. The remainder of the soil preparation was carried out as described for Example No 1.

(iii) Test Procedure The thread preparation, apparatus setup and test procedure was carried out in the same way as for Example 1.

(iv) Results The results of the tests were calculated and plotted in the same manner as for Example 1.

(v) Properties The plots of stress versus strain are presented in Figure 17. The plots of work per unit volume versus diameter are presented in Figure 18. The plots of work per unit volume versus moisture content are presented in Figure 19. A value for the Hardening Limit was not obtained from Figure 19 as there appears to be a wider transition from the lower limb to the upper limb. For the upper limb the Toughness Coefficient is 9.09. From this Coefficient for the upper limb the value of the toughness at the plastic limit is determined. Alternatively the value can be scaled from the plot in Figure 19. A value of 283 kJ/m3 was obtained.

For the lower limb the Toughness Coefficient is 0.794. From the Toughness Coefficient for the lower limb the value of T0 is determined, the moisture content at zero toughness, the Toughness Limit. Alternatively the value can be scaled from the plot in Figure 19. A value of 189% was obtained. )

Claims (28)

1. Claims An apparatus for the measurement of a plastic property of a

   substance, the apparatus comprising: (i) a base for receiving a sample of the substance; (ii) rolling means for rolling the sample over a known distance; (iii) pressure means for applying a known force to the sample during rolling so as to cause compression of the sample; and (iv) measurement means for measuring the compression of the sample.
2. 2. An apparatus according to claim 1, wherein the base comprises a first plate and the pressure means comprises a second plate, the second plate including control means for modifying the known force exerted at a given position by said second plate against a sample positioned between said plates.
3. 3. An apparatus according to claim 2, wherein the first and second plates are substantially parallel to one another.
4. 4. An apparatus according to claim 2 or 3, wherein the first plate is substantially horizontal and slidably associated with a platform such that the rolling means comprises the first plate moving relative to a generally stationary second plate.
5. 5. An apparatus according to any one or more of claims 1 to 4, wherein the measurement means comprises a gauge.
6. 6. An apparatus according to claim 5, wherein the gauge abuts the second plate and measures compression of the sample indirectly.
7. 7. An apparatus according to any one or more of claims 2 to 6, wherein the control means comprises one or more objects moveable between different positions on the pressure means so as to exert a given force at a given position to the sample. )
8. 8. An apparatus according to claim 7, wherein the object has a mass in the range of from 100 to 2500 g so as to exert a given range of forces at a given position to the sample.
9. 9. An apparatus according to any one or more of claims 2 to 8, wherein the second plate is configured so as to allow the sample to spread laterally andlor longitudinally during rolling.
10. 10. An apparatus according to any one or more of claims 2 to 9, wherein the first plate is configured so as to allow the sample to spread laterally andlor longitudinally during rolling.
11. 11. An apparatus according to any one or more of claims 1 to 10, wherein the apparatus comprises start and finish locators so as to determine the known distance over which the sample is rolled.
12. 12. A method for the measurement of a plastic property of a substance, the method comprising the steps of: (a) receiving a sample of the substance; (b) applying a known force to the sample; (c) rolling the sample under the known force over a known distance; and (d) measuring the compression of the sample caused by rolling the sample under the known force over the known distance.
13. 13. A method for the measurement of the toughness of a substance, the method comprising the steps of: (a) receiving a sample of the substance; (b) applying a known force to the sample; (c) rolling the sample under the known force over a known distance; (d) measuring the compression of the sample caused by rolling the sample under the known force over the known distance by measuring the reduction in width or diameter of the sample; (e) repeating steps (b) to (d) under different known forces until the sample reaches a given compression, or alternatively until the sample crumbles; (f) determining the moisture content of the sample, or a quantity functionally related thereto, when it has been reduced to the given compression (i.e. the given width or diameter), or has crumbled; (g) calculating the work done per cubic unit of volume of the sample for each value of force and compression for ten cycles of rolling; (h) plotting the cumulative work done per cubic unit of volume of the sample per set number of cycles of rolling against the width or diameter of the sample; and (I) determining the cumulative work done per cubic unit of volume of the sample per set number of cycles of rolling in reducing the width or diameter of the sample from about 6 mm to 3 mm so as to provide the toughness (T) at the particular moisture content.
14. 14. A method for the measurement of the plastic limit of a substance, the method comprising the steps of: conducting steps (a) to (i) as defined in claim 13 with a sample of a first moisture content, or a quantity functionally related thereto; (j) repeating steps (a) to (i) as defined in claim 13 with a sample having a different moisture content, or a quantity functionally related thereto, to the first moisture content or quantity functionally related thereto; (k) plotting the values of toughness of the substance at the particular moisture contents (or quantities functionally related thereto) against the moisture contents (or quantities functionally related thereto); and (I) determining the plastic limit of the substance from the plot in step (k) as the moisture content at the transition from the plastic to the brittle states.
15. 15. A method for the measurement of one or more toughness properties of a substance, the method comprising the steps of: conducting steps (a) to (k) as defined in claim 14 to provide a plot of toughness of the substance against moisture content (or a quantity functionally related thereto); (m) determining the plastic limit of the substance according to step (I) above and determining Tmax as the toughness of the substance at the plastic limit; andlor (n) detemiining the Toughness coefficient (Ic) of the substance as the gradient of the plot of toughness versus moisture content; andlor ) (o) determining the Toughness Limit (IL) as the moisture content at zero toughness; and/or (p) identifying the change in gradient of the plot of toughness versus moisture content and determining the Hardening Limit (HL) as the moisture content at the break in the gradient; and/or (q) determining the toughness(TH) at the Hardening Limit; and/or (r) determining the Toughness Index (TI) as the difference between the Toughness Limit and the Plastic Limit.
16. 16. The method according to any one or more of claims 12 to 15, further including the step of pre-forming the sample into a generally cylindrical shape.
17. 17. The method according to claim 16, wherein the sample has a width in the range of from 1 to 30 mm and a length in the range of from 15 to 450 mm.
18. 18. A method according to any one or more of claims 12 to 17, wherein the known force is in the range of from 0 to 100 N.
19. 19. A method according to any one or more of claims 12 to 17, wherein the known distance is in the range of from 25 to 500 mm.
20. 20. A method according to any one or more of claims 12 to 19, wherein the substance is soil.
21. 21. A method according to any one or more of claims 12 to 20, using the apparatus according to any one or more of claims I to 11.
22. 22. The use of the apparatus according to any one or more of claims 1 to 11 for the measurement of a plastic property of a substance.
23. 23. The use according to claim 22, wherein the plastic property is the plastic limit.
24. 24. The use according to claim 22, wherein the plastic property is toughness. )
25. 25. The use according to any one or more of claims 22 to 24, wherein the substance is soil.
26. 26. A kit for the measurement of a plastic property of a substance, the kit comprising an apparatus for the measurement of a plastic property according to any one or more of claims I to 11 and an apparatus for forming a sample into a generally cylindrical shape of a predetermined size comprising a tube for receiving the sample, pressure means for compacting and shaping the sample inside the tube and extraction means for extruding the sample from the tube.
27. 27. An apparatus for the measurement of a plastic property generally as herein described with reference to and/or as illustrated in the accompanying drawings.
28. 28. A method for the measurement of a plastic property generally as herein described with reference to and/or as illustrated in the accompanying drawings.