COMPACTION TESTS
Compaction tests are used to measure how soils respond to being mechanically compacted, and to identify the optimum water content for achieving maximum density. These tests are essential for assessing soil suitability in earthworks, embankments, and pavement construction. By understanding compaction behaviour, engineers can design and monitor ground improvement works that achieve the required strength and stability. Compaction tests are typically carried out on disturbed soil samples prepared in the laboratory.
NOTE: An “[Exp]” prefix signifies the guidance, which is based on professional experience of practicing geotechnical engineers and GEOCompass creators.
Determination of Dry Density / Moisture Content relationship
'Baby' description:
“Packs soil with different amounts of water to see what mix makes it the tightest and heaviest.”
Applicability:
Cohesive and cohesionless soils.
Max particle size of 20mm for 2.5kg and 4.5kg rammer
Max particle size of 37.5mm for Vibrating rammer
Parameter Obtained:
Water Content [%].
Moisture Content at which the Maximum Dry Density is achieved.
Sample Quality:
Disturbed.
Sample Size:
15-40kg for soils where 70% passes 20mm
Scheduling Guidance:
Need to specify compaction method:
1) 2.5kg rammer – for cohesive soils for bulk earthworks (embankments etc)
2) 4.5kg rammer – for cohesive soils where high degree of compaction is required (major road sub-base, fill under structures etc)
3) Vibrating rammer – for cohesionless soils, not very reliable and therefore Max/Mix Density test is preferred.
4) [Exp] Advisable to schedule some particle density tests alongside to ensure that sensible air voids curves are obtained
5) [Exp] Advisable to schedule hand shear vane determinations at each compaction test point, where sample is suitable (ie. cohesive) (15 tests in total)
Scheduling Guidance:
BS 1377-4 1990
Determination of Maximum and Minimum Dry Densities
'Baby' description:
“Finds out how heavy soil can get when packed super tight, and how light it is when really loose.”
Applicability:
Sands and Gravels
Parameter Obtained:
Determines a relation of soils Dry Density to its Maximum and Minimum possible densities.
Sample Quality:
Disturbed.
Sample Size:
16kg of sieved material for Gravels
Scheduling Guidance:
None
Reference Standard:
BS 1377-4 1990
Determination of the Moisture Condition Value (MCV)
'Baby' description:
“Squeezes soil with different wetness to see how stiff or soft it is at each level.”
Applicability:
Particle size <20mm
Parameter Obtained:
MCV
Sample Quality:
Disturbed.
Sample Size:
1.5kg of sieved (<20mm) soil
Significantly more “raw” material may be needed >6kg
Scheduling Guidance:
None.
Reference Standard:
BS 1377-4 1990
Determination of California Bearing Ratio
'Baby' description:
“Pushes a plunger into compacted soil to see how strong it is, like testing how easy it is to poke a road.”
Applicability:
Particle size <20mm
Parameter Obtained:
CBR.
Sample Quality:
Sample Size:
Circa 6kg of sieved material.
Scheduling Guidance:
Need to specify:
1 – Surcharge to represent the overlying road construction. BS 1377-4 Cl. 7.3.3.3 indicates 2kg per 70mm of road construction.
2 – [Exp] Advisable to schedule hand shear vane determinations at top and base of test mould, where sample is suitable (ie. cohesive) – 3 tests on top, 3 on base (6 tests in total)
3 – Tests may not be representative if >20mm fraction represents >25% of content.
Reference Standard:
BS 1377-4 1990