SPT Testing in Wigan – BS 5930 Standard Penetration Test

The split-spoon sampler drives into Wigan ground at 30 blows per 150 millimetres. A 63.5 kg automatic trip hammer drops 760 mm, recording penetration resistance every 75 mm. The rig sits on crawler tracks, manoeuvring through tight brownfield access off Wallgate or Scholes. We log the N-value against depth, note the groundwater strike, and bag disturbed samples for the lab. In Wigan, where the Middle Coal Measures weather to stiff clay and sandstone bands alternate with mudstone, the SPT blow count often jumps from 8 to refusal within a metre. That contrast matters for pile toe levels. The hammer energy is calibrated to BS EN ISO 22476-3, so the N60 value you see on the log is corrected, not raw. For sites near the Douglas valley, where alluvial silts mask the bedrock, we combine SPT with CPT testing to map the soft layer thickness before designing shallow foundations.

In Wigan, SPT refusal on sandstone can occur at 3 metres depth on one borehole and 11 metres on the next, 15 metres away. That is the Middle Coal Measures reality.

Process overview

Wigan's industrial expansion through the 1840s left a subsurface legacy that still shapes site investigation strategy today. Backfilled mill lodges, buried colliery shafts, and thick made ground overlying the Pennine Middle Coal Measures create abrupt vertical changes in bearing capacity. The SPT captures that transition by driving through the fill until refusal on competent rock or dense till. You see N-values below 4 in loose ash and clinker, then a sharp climb past 50 at the rockhead. That signature tells the structural engineer where to stop digging and start founding. On redevelopment plots around the former Pagefield Ironworks or the canal-side warehouses near Trencherfield Mill, we also run grain size analysis on the SPT wash samples to confirm the fines content in the silty sand seams. The combined data feeds directly into bearing capacity calculations under BS EN 1997-1 and helps avoid over-design on deep piles where a pad footing on dense glacial till would suffice.

Local context

A five-storey apartment block on a former dye works off Miry Lane. The borehole log showed 4 metres of loose sandy fill with N-values of 3 to 6, then a thin band of soft alluvial clay where N dropped to 2. Below that, dense glacial till gave N=22 and weathered sandstone refusal at N=50/50 mm. The structural team had initially assumed a ground-bearing slab at 1.5 metres depth. The SPT data forced a complete redesign to CFA piles socketed into the till, bypassing the compressible upper layers. Without that single borehole and its SPT profile, the building would have settled differentially within the first wet winter. In Wigan, skipping the penetration test on brownfield land is not a cost saving. It is a liability that the NHBC warranty inspector will flag immediately.

Technical parameters

Parameter	Typical value
Hammer type	Automatic trip, 63.5 kg mass
Drop height	760 mm ± 10 mm
Sampler standard	Split-spoon, BS 5930:2015
Energy calibration	BS EN ISO 22476-3, recorded Er
Reporting metric	N60 (energy-corrected blow count)
Seating drive	150 mm, blows logged separately
Test interval	1.50 m or at stratum change

Additional services

Dynamic Probe (DPSH) Testing

Lightweight continuous profiling across large Wigan brownfield sites where SPT boreholes are spaced at 20 metre centres. Quick correlation with N-value for fill thickness mapping.

Triaxial Compression Testing

Undrained and effective stress triaxial tests on undisturbed samples from the glacial till and Coal Measure clays beneath Wigan, providing c' and φ' for slope stability and retaining wall design.

Ground Gas Monitoring

Standpipe installations in SPT boreholes for long-term gas monitoring on former colliery land. Methane and carbon dioxide risk assessment to BS 8485 and CIRIA C665.

Pile Integrity Testing

Low-strain sonic integrity testing on CFA piles installed through the soft alluvial layers identified by SPT logs. Verification of pile length and shaft continuity.

Quick answers

What does an SPT test in Wigan typically cost?

For a standard SPT borehole in Wigan, budget between £460 and £650 per hole, depending on depth, access restrictions, and whether the rig is tracked or wheeled. That includes the engineer's time, the calibrated automatic hammer, sampling, groundwater observation, and the factual report with N60 values. Mobilisation to the site, traffic management on narrow terraced streets, and laboratory testing on disturbed samples are quoted separately after we review your site plan.

How deep do you need to drill for SPT in Wigan's Coal Measure geology?

Most Wigan investigations go to 10 or 15 metres, but the depth depends entirely on the site's mining history and the foundation type. For a shallow pad on a greenfield site near Standish, 5 metres into the glacial till might be enough. For a piled building on made ground near the town centre, we drill until we achieve SPT refusal (N>50) in competent sandstone or mudstone and then core at least 3 metres into the rock to prove it is not a floating boulder or a collapsed mine roof. The Coal Authority mining report is always cross-referenced before we set the final depth.

How quickly can I get SPT results after drilling in Wigan?

The field logs with raw N-values and groundwater observations are available the same day the rig demobilises. The final factual report with N60 energy-corrected values, exploratory hole location plan, and sample descriptions follows within 5 working days. If you need interpreted parameters for a tender submission, we can turn around the geotechnical interpretive report in 7 to 10 working days.