London’s subsoil profile is dominated by the London Clay formation, a stiff overconsolidated clay that can exceed 40 m in thickness. Over much of the city, this clay is capped by Terrace Gravels and made ground from centuries of urban development. When contractors compact fill for road subgrades, building pads, or utility trenches, they rely on the field density test (sand cone method) to verify that compaction meets specification. The test uses a calibrated sand of known density to measure the volume of a small excavated hole, giving a direct reading of in-situ dry density. For London’s mixed geology, this method is preferred because it works well in both cohesive soils like clay and granular fills like sandy gravel. Before placing structural fill, a Proctor compaction test establishes the target maximum dry density for each material type.
A single sand cone test on London Clay fill can reveal whether the contractor has achieved the required 95% of maximum dry density before the next lift is placed.
Scope of work
Area-specific notes
A sand cone density test in London requires a flat, undisturbed surface. On steep slopes or uneven made ground, the cone can leak sand, skewing the volume reading. The test also struggles in waterlogged excavations common after heavy London rainfall, where free water in the hole prevents accurate sand placement. Fills containing large rubble, frequent in Central London’s deep basement backfills, may require multiple test locations to get a representative average. Experienced technicians identify these conditions early and adjust the test layout accordingly, sometimes shifting to a nuclear density gauge when the sand cone method becomes impractical.
Standards used
BS 1377-9:1990 – Methods for test for soils for civil engineering purposes (in-situ density), Eurocode 7 (EN 1997-1:2004) – Geotechnical design, compaction control, Highways England Manual of Contract Documents (MCHW) Series 600 – Earthworks compaction
Linked services
Sand Cone Density (BS 1377-9)
Standard sand replacement test for cohesive and granular fills. Includes calibrated sand, volume measurement, moisture content, and dry density report.
Nuclear Gauge Density
High-volume compaction control using a troxler gauge for London infrastructure projects. Faster than sand cone but requires radioactive source licensing.
Compaction Test Package (Proctor + Field Density)
Combined lab Proctor test to establish target MDD and OMC, followed by field sand cone tests to verify compliance on site.
Large-volume Fill Density (Trench & Foundation)
Multiple sand cone tests per lift for deep utility trenches and foundation backfills in London clay and made ground.
This service complements our laboratory testing work for a complete project analysis.
Typical parameters
Q&A
How much does a sand cone density test cost in London?
A single sand cone field density test in London typically ranges from £70 to £110 per test point. This includes the field visit, calibrated sand, volume measurement, moisture content determination, and a written report. Volume discounts apply for projects requiring 10+ test points.
Can the sand cone method be used on wet London Clay?
Yes, but with caution. If the clay is so wet that free water pools in the test hole, the sand will not fill the cavity properly, leading to inaccurate volume readings. In such cases, we recommend delaying the test until the fill drains, or using a nuclear density gauge instead.
What is the difference between sand cone density and a nuclear gauge?
The sand cone method directly measures density by excavating a known volume of soil — it is the most accurate method for cohesive fills like London Clay. A nuclear gauge uses gamma radiation to estimate density indirectly and is faster, but it requires operator licensing and can be affected by chemical composition of the soil. Sand cone is preferred for small sites and clay fills.