Earthworks - Geotechnical Investigation and Design Tables - page 152

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For nuclear density measurement: Every 20 tests should be calibrated with results
of sand cone.

12.24 Standard versus modified compaction
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There is no direct conversion between modified and standard compactions.

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The table below is a guide, but should be checked for each local site material.

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In general modified compaction is applicable mainly to pavements. It should be
avoided in subgrade materials, and especially in expansive clay materials.

Table 12.24 Equivalence of modified and standard compactions (MDD).

Material Standard/modified compactions Modified/standard

Clays/silts 105-115% 85 to 95%

Sandy clays/clayey sands 110-100% 90 to 100%

Sands/gravels/crushed rock 105-100% 95 to 100%

12.25 Effect of excess stones
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The compaction tests are carried out for material passing the 20mm sieve.

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If the stone fraction is included, it is likely that density and CBR would be higher,
but with a lower OMC.

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The field density test that passes could be due to stone sizes influencing the results
rather than an acceptable test result as compared to the laboratory reference
density.

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The effect of stone size can be calculated, and depends on the quantity and type
of material.

Table 12.25 Typical stone size effects.

% of Stone sizes (% 20 mm) Actual density compared with lab density >

<

10% Negligible

20% 10% Higher ∼

40% 20% Higher ∼