The alluvial clays of Derby city centre behave very differently from the glacial tills found in the suburban estates of Littleover and Mickleover. That contrast matters when you need reliable shear strength parameters for foundation design. A direct shear test on undisturbed samples from the Derwent floodplain will typically yield lower cohesion values than tests on the stiff tills of the Chevin ridge. We run these tests in our UKAS-accredited laboratory following BS 1377-7:1990. The procedure is straightforward: we shear a square specimen under a constant normal load and record the peak and residual stress. Results come back within 5 working days. For projects in Derby, this test is the standard way to derive the angle of internal friction and cohesion for shallow foundation calculations.
Peak shear strength on Derby alluvial clays typically ranges from 28 to 34 degrees, with cohesion between 5 and 15 kPa.
Process overview
Local context
Derby expanded rapidly during the Industrial Revolution, with factories and railways built directly on soft alluvial deposits along the Derwent. Many of those 19th-century structures now sit on foundations that were never properly characterised. The risk is clear: differential settlement, bearing failure, and slope instability in cuttings. A direct shear test on undisturbed samples taken from beneath existing foundations gives you the real shear strength, not a guessed value. We have tested specimens from the Cathedral Quarter and the Pride Park development. The results consistently show that the upper 3 metres of the floodplain clay have lower friction angles than the deeper till. That knowledge directly informs foundation retrofit and new build designs.
Reference standards
BS 1377-7:1990 – Methods of test for soils: shear strength (direct shear), BS 1377-7/D3080M-11 – Standard Test Method for Direct Shear of Soils, Eurocode 7 (EN 1997-2:2007) – Geotechnical design, ground investigation
Additional services
Standard consolidated drained (CD) test
Three specimens at different normal stresses. Peak and residual strength reported. Suitable for Derby’s alluvial and till clays. Results in 5 days.
Multi-stage direct shear test
One specimen sheared at three increasing normal loads. Economical for small projects where sample quantity is limited. Common on Derby brownfield sites.
Residual shear test
Repeated forward and reverse shearing to measure post-peak strength. Required for slope stability analysis in the Derwent valley cuttings.
Typical parameters
Common questions
How much does a direct shear test cost in Derby?
A standard consolidated drained test on three specimens costs between £550 and £740, depending on the number of samples and required turnaround. Multi-stage tests are typically 20% lower.
What is the difference between direct shear and triaxial tests?
Direct shear tests shear the sample along a predefined horizontal plane, giving peak and residual friction angle. Triaxial tests apply confining pressure and can measure pore pressure. For Derby’s stiff tills, direct shear is faster and more cost-effective for routine design.
Can you test disturbed samples from Derby?
Yes, we can reconstitute disturbed samples to a target density and moisture content. This is common for fill materials from the Chevin or Sherwood Sandstone quarries. We report results as reconstituted shear strength.
How do I interpret the direct shear results for foundation design in Derby?
Peak friction angle and cohesion are used in bearing capacity equations (Terzaghi, Meyerhof) and slope stability analyses. For Derby alluvial clays, use the peak values for short-term stability and residual for long-term or cyclic conditions. We provide a summary sheet with recommended parameters.