The geology across Portsmouth splits in a way that directly impacts earthworks. Over on Portsea Island, where the naval dockyards and dense Victorian terraces sit, you're generally dealing with superficial deposits of brickearth and river terrace gravels over London Clay—material that can vary from stiff to surprisingly soft within a few metres. Cross the bridge to the mainland side around Cosham or Hilsea, and the chalk bedrock gets much closer to the surface, often with a thin, flinty cover. This variability means a compaction spec that works beautifully in the gravels near Fratton might need serious adjustment a mile north. The sand cone method—what BS 1377-9 calls the sand replacement method—gives us a direct, physical measurement of in-place density, and it's still the most practical way to verify compliance on a residential plot or a commercial pad where nuclear gauge logistics are a headache. When we're running multiple tests across a Portsmouth site, we often pair the density readings with laboratory Proctor tests to nail down the reference maximum dry density for that specific material, rather than relying on generic assumptions that can miss by a significant margin.
A sand cone test doesn't estimate density—it measures it directly by substituting a known-volume sand for the soil you excavate, which is why it remains the referee method when other techniques give borderline results.
Process overview
Local context
Portsmouth's geology includes significant thicknesses of compressible alluvium and soft silty clays in the lower-lying areas, particularly south of the A27 and across the reclaimed land around Port Solent. The groundwater table across much of Portsea Island sits barely 2 to 3 metres below ground level, and it fluctuates with the tides in the Solent. If fill placement proceeds without proper density control, you're not just risking excessive settlement—you're potentially creating a permeable layer that channels groundwater towards foundations or buried services. We've seen sites where poorly compacted trench backfill in the London Clay weathered zone led to differential settlement cracks in adjacent pavement within the first year. BS EN 1997-1:2004 (Eurocode 7) requires that the design assumptions about fill properties be verified, and the sand cone method provides the direct evidence that the placed material meets the specified unit weight and stiffness parameters. In coastal Portsmouth, with its combination of soft natural ground and imported engineered fill, skipping this verification step is a gamble that the long-term settlement behaviour will somehow meet the tight tolerances of the structural design.
Reference standards
BS 1377-9:1990: Methods of test for soils for civil engineering purposes – In-situ tests – Sand replacement method, BS EN 1997-2:2007 (Eurocode 7): Ground investigation and testing – Identification and classification of soil, Section 4.4 for density testing, BS 5930:2015+A1:2020: Code of practice for ground investigations – Section 37 for field density and compaction control, Manual of Contract Documents for Highway Works (SHW), Series 600: Earthworks compaction requirements
Additional services
Field Density by Sand Cone (ASTM/BS)
The standard sand replacement test performed to BS 1377-9. Includes excavation, moisture sample collection, volume determination with calibrated sand, and calculation of wet/dry density and relative compaction. Suitable for natural soils and granular fill with particle sizes up to 37.5 mm.
Compaction Verification Package
Combines on-site sand cone density testing with laboratory moisture content and Proctor compaction curves (BS 1377-4 or BS EN 13286-2 for aggregates). We deliver a turnkey package: field technician, calibrated equipment, lab testing, and a signed report comparing in-situ dry density against the target value.
Rapid Response Re-Testing
When the initial round shows marginal failures and the contractor re-compacts the lift, we can return to the Portsmouth site within short notice to re-test the same locations. The report clearly documents the sequence: initial result, corrective action taken, and final passing value—essential for the project's quality assurance trail.
Typical parameters
Quick answers
What does a field density test with the sand cone method typically cost in the Portsmouth area?
For sites around Portsmouth and the wider Hampshire area, a single sand cone density test generally runs between £80 and £130, depending on the number of tests scheduled on the same visit and whether companion lab testing—like moisture content or a one-point Proctor—is included. A full day of testing with multiple points and full reporting naturally brings the per-test rate down. We can provide a fixed-price quote once we know the site location, number of lifts, and the project's testing frequency specification.
How many sand cone tests do I need per lift on a Portsmouth residential development?
There is no single universal answer—it depends on the project's earthworks specification and the site area. A common rule of thumb for general fill on residential plots is one test per 500 square metres per compacted lift, with a minimum of three tests per lift on smaller footprints. For highway-adjacent works or adoptable roads, the SHW Series 600 often specifies tighter frequency. We review the engineering drawings and spec with you before the programme starts, and we flag any areas where the heterogeneity of Portsmouth's made ground suggests additional control points.
Can the sand cone method be used on crushed concrete or recycled aggregate fill?
Yes, it can, provided the maximum particle size doesn't exceed about 37.5 mm. For coarser recycled aggregate—common in larger Portsmouth commercial jobs—the standard 100 mm or 150 mm diameter sand cone hole may not give a representative volume, and we'd discuss moving to a larger replacement method using a calibrated membrane or plaster. The key is matching the test volume to the nominal maximum aggregate size, as required by BS 1377-9, so the density result genuinely represents the compacted layer.