Particle Size Distribution Analysis for Geotechnical Design in Milton Keynes

Milton Keynes owes its modern footprint to the 1967 New Town designation, which transformed a constellation of Buckinghamshire villages into a grid of boulevards and concrete canyons. That rapid expansion placed foundations directly on the region’s layered Quaternary geology—stiff Oxford Clay interbedded with lenses of glacial till and pockets of Oadby Member diamicton. A reliable grain size analysis (sieve + hydrometer) becomes the first quantitative filter for any earthworks specification here, because the difference between a sandy silt and a fat clay dictates everything from trench backfill permeability to seasonal heave potential. Our laboratory runs the full BS 5930 particle size distribution protocol on every borehole sample retrieved from Campbell Park to Bletchley, plotting the percentage passing from 63 mm down to the clay fraction below 2 µm. When the grading curve straddles multiple soil groups, we cross-check the hydrometer readings with Atterberg limits to pin the fines classification before the structural engineer commits to a bearing capacity model.

In Milton Keynes till, a shift of four percentage points in clay fraction often separates a free-draining sub-base from a moisture-sensitive formation that needs lime stabilisation.

Our approach and scope

The analysis starts on a stacked sieve column—typically 200 mm diameter brass frames holding stainless steel mesh from 63 mm down to 63 µm—mounted on a mechanical shaker that runs for a timed interval calibrated to the sample mass. Material retained on each sieve is weighed to 0.1 g resolution, and the cumulative passing percentages are plotted against a logarithmic aperture scale. For the sub-63 µm fraction we transfer a dispersed suspension into a sedimentation cylinder and lower a hydrometer conforming to BS 1377-2, taking readings at 0.5, 1, 2, 4, 8, 15, 30, 60, 120 and 1440 minutes while logging temperature for viscosity correction. A single CPT test profile near the extraction point often validates the layering inferred from the grading envelope, especially where thin sand stringers within the Oxford Clay control drainage behaviour more than the bulk clay percentage would suggest. Once the full PSD is digitised, we calculate D10, D30, D50 and D60 to derive the uniformity coefficient and coefficient of curvature directly, feeding those numbers into filtration and internal stability assessments for drainage blankets beneath the city’s balancing ponds.

Local considerations

We reviewed a warehouse extension near the M1 junction 14 where the contractor had assumed a uniform glacial sand from window samples, skipped the hydrometer stage and designed a shallow pad footing on an allowable bearing pressure of 150 kPa. The grain size analysis we ran afterwards on Shelby tube material revealed a 34% clay fraction—the formation was actually a matrix-supported diamicton with undrained shear strength below 60 kPa at 1.5 m depth. Differential settlement appeared within six months, cracking the slab at the expansion joint and requiring resin injection to stabilise the floor. That episode underlines why a sieve-only curve is worthless in Milton Keynes: the sand lenses visible in the auger cuttings mask a fine-grained matrix that governs consolidation rate and stiffness. Eurocode 7 mandates a minimum of two classification parameters for every design soil unit, and the combined sieve-plus-hydrometer PSD paired with plasticity data satisfies that requirement while flagging frost-susceptible silts before they end up beneath an unheated industrial slab.

Technical data

Parameter	Typical value
Test standard	BS 5930:2015 + A1:2020; BS 1377-2:1990
Sieve range	63 mm down to 63 µm (coarse to fine sand fraction)
Hydrometer method	Sedimentation analysis, 0.5 min to 24 h readings
Sample mass (dry)	200 g to 5 kg depending on maximum particle size
Reporting metrics	D10, D30, D60, Cu, Cc, % gravel/sand/silt/clay
Dispersion agent	Sodium hexametaphosphate solution, concentration per BS 1377
Minimum sample for hydrometer	50 g passing 63 µm sieve

Other technical services

Atterberg Limits Determination

Liquid limit, plastic limit and plasticity index measured on the fraction passing 425 µm, following the cone penetrometer method of BS 1377-2. Combined with the PSD, these values place the soil on the Casagrande chart and confirm whether the clay fraction is active enough to drive shrink-swell behaviour in the weathered Oxford Clay.

Triaxial Compression Testing

Consolidated undrained and drained triaxial tests on 100 mm specimens trimmed from undisturbed samples, providing effective stress strength parameters (c' and φ') for the same units that the grain size analysis has classified. Essential when the grading curve indicates a transitional soil that does not behave purely drained or undrained.

Reference standards

BS 5930:2015 + A1:2020 — Code of practice for ground investigations, BS 1377-2:1990 — Methods of test for soils for civil engineering purposes (classification and compaction tests), Eurocode 7: BS EN 1997-1:2004 + UK National Annex, BS EN ISO 17892-4:2016 — Determination of particle size distribution

Frequently asked questions

What does a grain size analysis cost in Milton Keynes, and how long does it take?

A combined sieve and hydrometer analysis on a single sample typically falls between £80 and £170, depending on whether the sample requires pre-treatment to remove organics or carbonates. Standard turnaround is five working days from sample receipt; we can deliver results in 48 hours for an urgent specification if the laboratory schedule allows.

Which British Standards govern particle size distribution testing for UK construction?

The primary documents are BS 5930:2015 for ground investigation practice and BS 1377-2:1990 for the actual laboratory procedures. BS EN ISO 17892-4:2016 provides the harmonised European method, and Eurocode 7 (BS EN 1997-1:2004) requires PSD data as part of the geotechnical investigation for every design soil unit encountered on site.

Can the hydrometer analysis reliably detect the clay fraction in Milton Keynes glacial till?

Yes, provided the sample is properly dispersed and temperature-corrected. Milton Keynes tills often contain aggregated clay particles that require extended mixing with sodium hexametaphosphate to break down. We check for complete dispersion by running a duplicate reading after 24 hours; if the values diverge by more than 2%, we extend the chemical pre-treatment and repeat the sedimentation run.