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Direct shear testSoil mechanics study
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Differential settlement analysisSettlement analysisFoundations on fill (analysis)Seismic foundation designMicropile design
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Direct Shear Test in Cardiff – Geotechnical Laboratory Service

Evidence-based design. Reliable delivery.

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Cardiff grew fast during the 19th-century coal boom, turning tidal marshes and reclaimed docklands into the city centre we know today. That history matters because much of the ground beneath the urban core consists of soft alluvial clays, glacial tills, and made ground from old railway sidings. For any project here, knowing the drained shear strength of those materials is essential. We run the direct shear test in Cardiff as a reliable way to obtain cohesion and friction angle values for slope stability and foundation design. The test follows BS 1377-7:1990, giving engineers parameters they can trust when checking bearing capacity or lateral earth pressures. Before we set up the shear box, we often recommend a complementary asentamiento differential analysis to identify potential differential movements in layered profiles.

Cardiff
In Cardiff's alluvial clays, the direct shear test provides effective stress parameters that are critical for slope stability and foundation design under drained conditions.

Our service areas

Foundations

Differential settlement analysis ›Settlement analysis ›Foundations on fill (analysis) ›Seismic foundation design ›Micropile design ›
VIEW ALL FOUNDATIONS ›

Slopes & Walls

Slope stability analysis ›Retaining wall design ›MSE (Mechanically Stabilized Earth) wall design ›
VIEW ALL SLOPES & WALLS ›

Improvement

Geotechnical drainage design ›Jet grouting design ›Organic soil management ›
VIEW ALL IMPROVEMENT ›

This service complements our laboratory testing work for a complete project analysis.

Process overview

The glacial tills around Cardiff are typically dense, with SPT N-values above 30, while the alluvial clays along the Taff and Ely floodplains can be soft to firm, with undrained strengths as low as 30 kPa. In those softer materials, the direct shear test in Cardiff becomes particularly useful for measuring effective stress parameters under slow drainage conditions. We run both consolidated-drained and consolidated-undrained procedures depending on the project stage. A key advantage of this test is the ability to test along pre-existing failure planes or at different orientations when dealing with anisotropic soils. For embankment works on the M4 corridor, we pair the direct shear results with a slope stability check to verify long-term safety factors. When fill is involved, we also combine the test with a drainage geotechnical study to ensure pore pressures are properly controlled during construction.

Local context

The difference between Cardiff Bay and the northern suburbs is stark. In the Bay, reclaimed dockland with soft estuarine silts means a direct shear test alone might not capture the full risk — you need to check for organic content and potential gas pockets. Up towards Llandaff and Whitchurch, the glacial tills are stiffer but can contain cobbles that disturb the shear plane. If the sample is disturbed, the resulting cohesion value drops artificially, leading to over-conservative designs. That is why we always inspect the sample before trimming and reject any block with visible fissures or gravel intrusions.

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Relevant standards

BS 1377-7:1990 – Methods of test for soils: shear strength (direct shear), BS 1377-7 – Standard Test Method for Direct Shear Test of Soils, Eurocode 7 (EN 1997-1:2004) – Geotechnical design: partial factor application

Typical values

ParameterTypical value
Test standardBS 1377-7:1990 / BS 1377-7
Sample size60 mm x 60 mm square or 50 mm diameter circular
Shear rate range0.0001 to 2.0 mm/min
Normal stress range12.5 to 800 kPa
Parameters obtainedEffective cohesion (c'), friction angle (φ')
Sample preparationUndisturbed block or remoulded compaction
Reporting time5–7 working days from sample receipt

Q&A

What is the difference between direct shear and triaxial test for Cardiff clays?

The direct shear test forces failure along a predetermined horizontal plane, which works well for soils with distinct bedding or fissures. The triaxial test allows failure along the weakest plane naturally, so for uniform alluvial clays in Cardiff, triaxial often gives more representative results. However, direct shear is faster, cheaper, and preferred for granular fills and interface testing.

How much does a direct shear test cost in Cardiff?

The typical cost for a single direct shear test in Cardiff ranges from £500 to £630, depending on the test type (CD, CU, multi-stage) and the number of normal stress levels. Volume discounts apply for projects requiring multiple tests, and we include full reporting with graphs of shear stress vs. displacement.

Can the direct shear test be used for Cardiff's made ground and demolition fill?

Yes, but only if the sample can be trimmed without large particles disturbing the shear plane. For made ground containing brick, concrete, or cobbles above 10 mm, we recommend a large-scale direct shear apparatus (300 mm shear box) or a triaxial test with gravel correction. The standard 60 mm box is unsuitable for heterogeneous fill.

What sample quality is required for a direct shear test in Cardiff?

Undisturbed block samples taken from test pits or thin-walled tube samples are preferred. The sample must be intact with no visible desiccation cracks or gravel inclusions. For remoulded tests, we need at least 5 kg of representative soil compacted to the target density and moisture content. All samples should be sealed and delivered within 24 hours of extraction.

Location and service area

We serve projects across Cardiff.

Location and service area