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Grain Size Analysis (Sieve & Hydrometer) for Dublin Construction Projects

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On Dublin sites, the story of the ground is often written in the grain size. Boulder clay lodgement till covers much of the city, but it is rarely uniform—it shifts from sandy lenses near the coast to stony, matrix-supported diamicton only a mile inland. Our grain size analysis (sieve plus hydrometer) maps this full range, quantifying gravel, sand, silt, and clay fractions from the coarse fraction down to the colloidal 2-micron range, because a bulk description of 'brown boulder clay' is simply not enough to design a working drainage blanket, assess frost susceptibility, or confirm compliance with the TII Specification for Road Works Series 600 earthworks. We run the hydrometer test to ASTM D7928 procedure with sodium hexametaphosphate dispersion, which is critical for the marine-influenced clays found in the Docklands and along the Tolka estuary, and we cross-check the fines content with Atterberg limits testing whenever the hydrometer curve suggests a plasticity shift that could affect the Unified Soil Classification System (USCS) designation.

A single hydrometer curve on Dublin lodgement till reveals more about drainage and frost behaviour than twenty hand-auger descriptions combined.

Process overview

Dublin’s urban expansion, from the Georgian cores around Merrion Square to the modern apartment blocks in Sandyford, has piled decades of made ground over the natural drift. Testing the full particle size distribution on these sites means separating what is natural from what is imported. Our lab processes samples through a nest of sieves from 75 mm down to 63 µm, then moves the minus-63 µm suspension into a sedimentation cylinder for the hydrometer analysis. The combined curve gives the engineer precise values for D10, D30, D60, and the coefficient of uniformity (Cu), numbers that feed directly into filter design and seepage calculations. When the fines content climbs above 12% in a structural fill, we often recommend a Proctor compaction test to determine maximum dry density at the same gradation, because a shift of only three percent in minus-75 µm material can drop the CBR by half on a poorly graded Dublin sand. Our report tabulates percent gravel, sand, silt, and clay by mass, plots the full semilogarithmic curve, and flags any gap-graded intervals that might cause internal instability in a drainage layer.
Grain Size Analysis (Sieve & Hydrometer) for Dublin Construction Projects
Technical reference — Dublin

Local context

The Dublin climate plays a direct role in how grain size data gets used—or misused. With 128 wet days a year on average and a water table that sits within two metres of the surface across much of the city, a poorly graded fine sand classified as SP under the USCS can become unstable the moment a contractor opens a trench below the groundwater line. We have seen cases in Rathmines and Ranelagh where the grain size curve looked acceptable on paper, but the silt content was just high enough to hold capillary water, turning the excavation into slurry after three days of steady drizzle. Our hydrometer analysis catches those borderline silt fractions early, so the designer can specify dewatering or a filter fabric with an appropriate AOS opening size. For brownfield sites in the Liberties and the docklands, where historical fill often contains brick dust and ash that skew the fines curve, we combine the grain size analysis with a sand cone density test to verify that the placed fill actually meets the compaction specification at the measured gradation—because a Proctor curve built on the wrong particle size distribution guarantees a failing relative density result.

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Reference standards

IS EN ISO 17892-4:2016 – Geotechnical investigation and testing – Laboratory testing of soil – Part 4: Determination of particle size distribution, ASTM D7928-21 – Standard Test Method for Particle-Size Distribution (Gradation) of Fine-Grained Soils Using the Sedimentation (Hydrometer) Analysis, TII Specification for Road Works, Series 600 – Earthworks (Ireland)

Technical data

ParameterTypical value
Sieve range (coarse fraction)75 mm down to 63 µm (ASTM E11 sieves)
Hydrometer analysis range63 µm down to 0.2 µm (ASTM 152H hydrometer)
Dispersion methodSodium hexametaphosphate, 40 g/L solution
Sample mass (composite)500–2000 g oven-dried, depending on maximum particle size
Reported parametersD10, D30, D60, Cu, Cc, % gravel/sand/silt/clay
Applicable Irish standardIS EN ISO 17892-4:2016
Sample preparationWet sieving at 63 µm before hydrometer; oven-dry at 105°C

Common questions

How long does a full sieve and hydrometer test take on a Dublin project?

The combined test typically takes five to seven working days from sample receipt to final report. The hydrometer phase alone requires a minimum 24-hour sedimentation period with readings at 2, 5, 15, 30, 60, 250, and 1440 minutes, plus temperature correction and a parallel blank hydrometer cylinder. We dispatch the PDF report with the semilogarithmic grain size curve, tabulated percent fractions, and USCS classification as soon as the final reading is validated.

What sample mass do you need for a combined sieve and hydrometer analysis?

We require approximately 1000 g of oven-dried material passing the 4.75 mm sieve for the hydrometer portion, plus sufficient bulk material to run the full coarse sieve stack. For a typical Dublin lodgement till with gravel clasts up to 75 mm, we request a 15–20 kg bulk sample in a sealed plastic bag, delivered to our lab within 48 hours of extraction to preserve the natural moisture content.

What does the grain size analysis cost for a typical Dublin site?

A full combined sieve and hydrometer test, including wet sieving, sedimentation, oven drying, and the complete report with USCS classification, falls in the range of €90 to €170 per sample depending on the maximum particle size and the number of samples submitted together. Volume pricing applies for earthworks control programmes with more than ten samples per month.

Do you use sodium hexametaphosphate as the dispersing agent, and does it affect the results on Dublin clays?

Yes, we use a 40 g/L sodium hexametaphosphate solution as the standard dispersant per ASTM D7928. On the calcareous Dublin boulder clay, which contains variable amounts of calcium carbonate from the underlying limestone, the dispersant is particularly important to prevent flocculation of the clay fraction and ensure a true particle size distribution. We adjust the concentration when the soil pH exceeds 8.5 to avoid over-dispersion of carbonate fines.

Location and service area

We serve projects across Dublin and surrounding areas.

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