Preparation of sample The sample should be prepared in accordance with the

soil is susceptible to crushing. When using Table 4.2.3 or 4.2.5, it can be useful to have more than 5 prepared sub-samples, in case further points need to be established on the compaction curve.

4.3.5 Test procedure

4.3.5.1 The mould including the base-plate is first weighed to an accuracy of 1 gm for medium gravel and 5 gms for coarse gravel (m1). Measure the internal dimensions to 0.1 mm

for medium gravel and 0.5 mm for coarse gravel size.

4.3.5.2 Attach the extension (collar) to the mould and place the mould assembly on a solid base, e.g. a concrete floor.

4.3.5.3 The prepared sample of moist material is divided into three approximately equal portions.

4.3.5.4 Sufficient material from the first portion is then placed in the mould so that the mould is about a third full when the soil has been compacted. This first layer is then compacted using 27 blows for 1L mould and 62 blows for CBR mould of the 2.5 kg rammer dropping from a controlled height of 300 mm. The blows should be evenly distributed over the surface of the material and care should be taken to ensure that soil does not stick to the face of the hammer, thus reducing the height of fall.

4.3.5.5 Material from the second and third portions is then placed in the mould, each portion being compacted as above. The purpose of this procedure is to compact the soil in three equal layers and on completion, the mould should be completely filled. On removal of the collar, the top surface of the soil should be proud of the top rim of the mould body by an amount not exceeding 6 mm. If the soil is below the top rim of the mould or is proud of the mould by more than 6 mm, the test must be repeated.

4.3.5.7 The soil above the mould rim should then be struck off level with a metal straight edge. With some coarse-grained materials it may be difficult to obtain a smooth surface. Replace any coarse particles, removed in the leveling process, by finer material from the sample, well pressed in.

4.3.5.7 The mould, base-plate and soil are then weighed, to an accuracy of 1 gram for 1L mould and 5 gram for CBR mould (m2).

4.3.5.8 Remove the compacted soil from the mould and place it on the metal tray. Take a representative sample for determination of moisture content.

4.3.5.9 For soils not susceptible to crushing break up the remainder of the soil, rub it through the 20 mm sieve and mix with the remainder of the prepared test sample. In case of soils susceptible to crushing, discard the remaining soil from each of the 5 approximately 2.5 kg representative sub-samples.

4.3.5.10 Increase moisture 1% to 2% for sandy or gravelly soils and 2% to 4% for cohesive soils and mix thoroughly into the soil. As the test progresses, the size of the increments can be decreased to increase accuracy in determining the optimum moisture content. 4.3.5.11 Repeat steps 4.3.5.3 to 4.3.5.10 to give a total of at least 5 determinations. The

moisture contents shall include the optimum moisture content, at which the maximum dry density occurs, this point being as near to the middle of the range as is practicable to achieve.

Note. Tables 4.2.2 to 4.2.5 recommend that samples of prepared soil be allowed to “cure” for 24 h before test, particularly if they are cohesive. Good laboratory

more than 5 prepared sub-samples, in case further points need to be established on the compaction curve.

4.3.5 Test procedure

4.3.5.1 The mould including the base-plate is first weighed to an accuracy of 1 gm for medium gravel and 5 gms for coarse gravel (m1). Measure the internal dimensions to 0.1 mm

for medium gravel and 0.5 mm for coarse gravel size.

4.3.5.2 Attach the extension (collar) to the mould and place the mould assembly on a solid base, e.g. a concrete floor.

4.3.5.3 The prepared sample of moist material is divided into three approximately equal portions.

4.3.5.4 Sufficient material from the first portion is then placed in the mould so that the mould is about a third full when the soil has been compacted. This first layer is then compacted using 27 blows for 1L mould and 62 blows for CBR mould of the 2.5 kg rammer dropping from a controlled height of 300 mm. The blows should be evenly distributed over the surface of the material and care should be taken to ensure that soil does not stick to the face of the hammer, thus reducing the height of fall.

4.3.5.5 Material from the second and third portions is then placed in the mould, each portion being compacted as above. The purpose of this procedure is to compact the soil in three equal layers and on completion, the mould should be completely filled. On removal of the collar, the top surface of the soil should be proud of the top rim of the mould body by an amount not exceeding 6 mm. If the soil is below the top rim of the mould or is proud of the mould by more than 6 mm, the test must be repeated.

4.3.5.7 The soil above the mould rim should then be struck off level with a metal straight edge. With some coarse-grained materials it may be difficult to obtain a smooth surface. Replace any coarse particles, removed in the leveling process, by finer material from the sample, well pressed in.

4.3.5.7 The mould, base-plate and soil are then weighed, to an accuracy of 1 gram for 1L mould and 5 gram for CBR mould (m2).

4.3.5.8 Remove the compacted soil from the mould and place it on the metal tray. Take a representative sample for determination of moisture content.

4.3.5.9 For soils not susceptible to crushing break up the remainder of the soil, rub it through the 20 mm sieve and mix with the remainder of the prepared test sample. In case of soils susceptible to crushing, discard the remaining soil from each of the 5 approximately 2.5 kg representative sub-samples.

4.3.5.10 Increase moisture 1% to 2% for sandy or gravelly soils and 2% to 4% for cohesive soils and mix thoroughly into the soil. As the test progresses, the size of the increments can be decreased to increase accuracy in determining the optimum moisture content. 4.3.5.11 Repeat steps 4.3.5.3 to 4.3.5.10 to give a total of at least 5 determinations. The

moisture contents shall include the optimum moisture content, at which the maximum dry density occurs, this point being as near to the middle of the range as is practicable to achieve.

practice should allow this is most cases. However, and in particular when testing sandy or gravelly soils, it may be possible to reduce or omit this requirement altogether. In the latter case, an estimate can be made of the likely optimum moisture content, and the first sub-sample made up and compacted immediately at that moisture content, following the procedures in 4.3.5.1 to 4.3.5.8.. The necessary weighings and calculations should be recorded on the test sheet. The compaction procedure is then repeated on two further sub-samples, at appropriate moisture contents above and below the estimated optimum. At this stage an estimate can be made of the dry densities of the specimens, using the calculated bulk densities and the assumption that the moisture contents are in fact what they were made up to be. From this information it can be determined where the three points are likely to lie on the final moisture content / dry density relationship curve, and the remaining specimens can then be moistened and compacted accordingly. This method can achieve reliable results on suitable soils if carefully carried out.

4.3.6 Calculation and expression of results

4.3.6.1 Calculate the internal volume of the mould. V (in cm3).

4.3.6.2 Calculate the bulk density, ρ (in Mg/m3) of each of the compacted specimens from the equation

ρ = m m V

2− 1

where, m1 is the mass of mould and base-plate (in g);

m2 is the mass of mould, base-plate and compacted soil (in g).

Note. Where the height of the compacted soil specimen is the same as the height of the compaction mould body, e.g. in the case of the 2.5 kg and 4.5 kg rammer methods, the mould factors can be used to calculate the bulk density of the soil as; ρ = m m x F H 2− 1   

In the vibrating hammer test, where the height of the compacted soil specimen may be different from the height of the compaction mould body the calculation then becomes

ρ = m m x F H - h

2− 1

Refer to Part 4.5 and Forms 4.3.1 to 4.3.4.

The dry density ρd of each compacted specimen is then calculated (in kg/m 3

) using the formula;

Dry density, ρ_d = x ρ 100 100 + w

testing sandy or gravelly soils, it may be possible to reduce or omit this requirement altogether. In the latter case, an estimate can be made of the likely optimum moisture content, and the first sub-sample made up and compacted immediately at that moisture content, following the procedures in 4.3.5.1 to 4.3.5.8.. The necessary weighings and calculations should be recorded on the test sheet. The compaction procedure is then repeated on two further sub-samples, at appropriate moisture contents above and below the estimated optimum. At this stage an estimate can be made of the dry densities of the specimens, using the calculated bulk densities and the assumption that the moisture contents are in fact what they were made up to be. From this information it can be determined where the three points are likely to lie on the final moisture content / dry density relationship curve, and the remaining specimens can then be moistened and compacted accordingly. This method can achieve reliable results on suitable soils if carefully carried out.

4.3.6 Calculation and expression of results

4.3.6.1 Calculate the internal volume of the mould. V (in cm3).

4.3.6.2 Calculate the bulk density, ρ (in Mg/m3) of each of the compacted specimens from the equation

ρ = m m V

2− 1

where, m1 is the mass of mould and base-plate (in g);

m2 is the mass of mould, base-plate and compacted soil (in g).

Note. Where the height of the compacted soil specimen is the same as the height of the compaction mould body, e.g. in the case of the 2.5 kg and 4.5 kg rammer methods, the mould factors can be used to calculate the bulk density of the soil as; ρ = m m x F H 2− 1   

In the vibrating hammer test, where the height of the compacted soil specimen may be different from the height of the compaction mould body the calculation then becomes

ρ = m m x F H - h

2− 1

Refer to Part 4.5 and Forms 4.3.1 to 4.3.4.

The dry density ρd of each compacted specimen is then calculated (in kg/m 3

) using the formula;

Dry density, ρ_d = x ρ 100 100 + w

The determined moisture content should be within 1% of the required moisture content if the mixing and testing has been carried out correctly.

The graph of dry density vs moisture content is then plotted as in Figure 4.1.1. The points should be joined by a curve of best fit.

The maximum dry density (MDD) and corresponding optimum moisture content (OMC) are then determined from the graph. Read off these values to three significant figures. Note. The maximum on the curve may lie between two points, but when drawing

the curve, care should be taken not to exaggerate its peak.

4.3.6.3 If required, curves corresponding to air void contents can be plotted on the same graph (see Figure 4.1.1). These are calculated from the equation

ρ ρ ρ d s = 1 - V 100 1 - w 100 a w

where, ρd is the dry density (in kg/m 3

);

ρs is the particle density (in kg/m 3

);

ρw is the density of water (in kg/m 3

), assumed equal to 1;

Va is the volume of air voids in the soil expressed as a percentage of

the total volume of the soil (equal to 0%, 5%, 10% for the purpose of the example);

w is the moisture content (in %).