The difference between a project on the dry, high ground of Broughty Ferry and one on the soft alluvial soils along the Tay estuary in Dundee could not be starker. In the Ferry you might find dense glacial till and sandstones; down by the river you get soft clays and silts with a high water table. Every time we start a factor of safety calculation in Dundee, we first look at that local geology. It dictates everything from the partial material factors we apply to the critical failure surface we model. For a slope near the Law, we combine field data with a clasificación de suelos to classify the till before running limit equilibrium analyses. That initial step saves a lot of rework later.
Eurocode 7 demands distinct partial factors for actions, materials and resistances — not a single lumped safety factor.
Process overview
Local context
We use a portable cone penetration rig for most of our factor of safety work in Dundee, especially on tight residential sites near Magdalen Green or the Perth Road. The rig weighs about 2.5 tonnes and pushes a 10 cm² cone at 20 mm/s. It gives continuous profiles of tip resistance and sleeve friction. That direct data feeds into the undrained shear strength for short-term stability calculations. Without it, you rely on empirical correlations that can mislead you in layered soils. In our experience, the biggest risk in Dundee is underestimating pore pressures in the soft clays during excavation — a good factor of safety calculation catches that early.
Reference standards
BS EN 1997-1:2004 (Eurocode 7 – Geotechnical Design), BS 5930:2015 (Code of Practice for Ground Investigations), NCEER 2001 (Youd & Idriss – Liquefaction Resistance), BS 1377-7 (Direct Shear Test of Soils)
Additional services
Field Cone Penetration Testing (CPT)
Continuous profiling of tip resistance and sleeve friction to derive undrained shear strength and soil behaviour type, essential for FS in soft clays.
Laboratory Direct Shear & Triaxial Tests
Drained and undrained shear strength parameters on undisturbed samples, performed in our UKAS-accredited lab following BS 1377 procedures.
Slope Stability Modelling (Limit Equilibrium)
2D and 3D analyses using Bishop, Spencer and Morgenstern-Price methods, calibrated against local Dundee soil data and groundwater conditions.
Geotechnical Interpretation & Reporting
Full FS calculation report with partial factors per EC7, including sensitivity analysis on critical slip surfaces and groundwater effects.
Typical parameters
Quick answers
What is the difference between a global safety factor and Eurocode 7 partial factors?
A global factor applies a single number (say 1.5) to the whole system. Eurocode 7 uses separate partial factors for loads (γF), materials (γM) and resistances (γR). For Dundee clays, we apply γM = 1.6 to cohesion and γM = 1.25 to tan φ'. This approach gives more consistent reliability across different failure modes.
How much does a factor of safety calculation service cost in Dundee?
For a typical residential or small commercial project in Dundee, the cost ranges from £460 to £1,370. This includes field testing (CPT or boreholes), lab shear strength tests and a full FS calculation report. Larger slopes or complex geology may increase the price.
Which soil types in Dundee require the most careful factor of safety analysis?
The soft alluvial clays and silts along the Tay estuary are the most critical. They have low undrained shear strength (20–40 kPa) and high plasticity. We also pay close attention to loose sand lenses that can liquefy under seismic or dynamic loading. The glacial till on higher ground is generally competent but can contain cobbles that disturb sampling.