BS 5930 and Eurocode 7 (EN 1997-1:2004) set the framework for in-situ bearing capacity verification across the UK, and in Derby these standards are particularly relevant given the city's mix of alluvial terrace deposits and glacial till over Mercia Mudstone. The plate load test (PLT) remains the most direct method to validate design assumptions before foundation construction, especially when working near the River Derwent floodplain where groundwater levels fluctuate seasonally. We perform the test using a hydraulic jack system against a kentledge reaction, recording load versus settlement increments to derive the modulus of subgrade reaction. Before mobilising the kit, we often cross-reference with an ensayo SPT profile to select the correct test depth and plate diameter.
A well-executed PLT in Derby's glacial till typically yields a modulus of subgrade reaction between 40 and 80 MN/m³ at 0.1 % plate settlement.
Process overview
- Immediate settlement at each load increment
- Modulus of subgrade reaction (k-value)
- Ultimate bearing capacity from the load-settlement curve
Local context
The hydraulic jack and reaction frame weigh around 1.5 tonnes, so lifting and positioning in confined Derby city-centre sites requires careful planning. We use a three-point spreader beam and manual chain blocks to avoid overhead hazards. The main operational risk is heave or rotation of the kentledge blocks if the ground is uneven — we always place a 25 mm steel spreader plate underneath to distribute the reaction load. During the test, a sudden bearing failure shows as uncontrolled settlement beyond 10 % of plate diameter; we stop the test immediately and record the failure load. For sites near the Derwent, we monitor the weather window to avoid rain softening the test surface.
Reference standards
BS 1377-9:1990 — In-situ tests (Part 9: Plate Loading Test), Eurocode 7 (EN 1997-1:2004) — Geotechnical design, BS 5930:2015 — Code of practice for ground investigations, UKAS ISO/IEC 17025 — Laboratory accreditation for calibration and testing
Additional services
PLT at Formation Level
Test carried out at the base of the excavation to verify the design bearing pressure for strip or pad footings, with full load-settlement reporting within 48 hours.
PLT in Trial Pits
Lowering the plate assembly into a 1.5 m deep pit to test the glacial till directly, using a mini reaction frame and smaller 300 mm plate.
Seasonal Moisture Correction
When testing during wet periods, we apply the BS 1377 correction for surface saturation to avoid underestimating the modulus of subgrade reaction.
Combined PLT + CBR Correlation
For pavement and sub-base designs, we run the plate test adjacent to a CBR mould to build a site-specific correlation between k-value and CBR.
Typical parameters
Common questions
What is the difference between a plate load test and a CBR test?
A PLT measures bearing capacity and settlement under a large plate (typically 600 mm) simulating a foundation, while a CBR test uses a 50 mm plunger to assess subgrade stiffness for pavement design. They serve different design stages.
How deep should the plate be tested in Derby?
The test is normally performed at formation level, which in Derby is typically 1.0–1.8 m below ground to reach the glacial till. If the design calls for deeper verification, we lower the assembly into a trial pit.
Can a PLT be done on a sloping site?
Yes, but we need a level reaction surface. We use a smaller plate and a custom levelling frame to accommodate gradients up to 10 degrees. The procedure remains unchanged per BS 1377-9.
How much does a plate load test cost in Derby?
For a standard 600 mm plate test with full reporting, the range is £600 – £1,150 depending on site access, depth, and number of load increments. A mobilisation fee may apply for sites outside the Derby ring road.