A five-storey mixed-use block near Reading Station required foundation depths on a site that had been redeveloped three times since the 1960s. Boreholes alone could not map the buried services and old basement obstructions with enough lateral resolution. We deployed a 20-tonne CPT rig along a tight 15-metre grid, pushing through made ground and River Terrace Deposits to refusal on the chalk at 14 metres. The continuous cone resistance trace picked up a soft lens at 6 metres that a standard SPT interval would have missed entirely. In Reading’s compressed urban plots, where access is limited and the underlying geology shifts from London Clay in the east to chalk and gravels in the centre, the CPT gives us a near-continuous log without cuttings, without spoil, and with real-time data that feeds straight into the ground model. Combining it with spt drilling on the same site lets us calibrate strength parameters with physical samples where the stratigraphy gets complex.
CPT in Reading's Thames Valley gravels gives us a stratigraphic resolution of 2 cm—boreholes alone cannot match that on mixed-fill brownfield sites.
Local geotechnical context
Reading’s winter groundwater regime, with the Kennet and Thames at full stage, saturates the alluvial silts and raises artesian pressure in the chalk below. Running CPT without pore pressure measurement under these conditions is a gamble on effective stress. We measure u2 at the cone shoulder and track excess pore pressure during pauses; a slow dissipation curve in a silt layer flags drainage problems that will delay consolidation under foundation load. In the town centre, historical channels and mill races—some backfilled in the 19th century—create soft spots that a widely spaced grid misses. Our standard grid in urban Reading is 15–20 metres, tightened to 8–10 metres where the site history suggests variable fill. On sloping sites near Caversham, we correlate CPT tip resistance with drained shear strength to check that temporary cut slopes will stand up during excavation, referencing the soil descriptions in BS 5930:2015+A1:2020 for consistency with the wider ground investigation report.
Common questions
What depth can a CPT reach in Reading’s ground conditions?
In the Thames Valley gravels and London Clay around Reading, a 200 kN rig typically reaches 18 to 22 metres before refusal on chalk. On gravel-dominated sites in the town centre, refusal may come earlier if the cone encounters dense flint beds. We assess anticipated refusal depth from nearby borehole records before mobilising.
How much does a CPT investigation cost for a typical Reading site?
For a standard CPT sounding in Reading, budget between £130 and £180 per metre of penetration. A one-day campaign with five soundings to 15 metres would fall in the £9,750 to £13,500 range. The exact figure depends on access, traffic management if working on the highway, and whether seismic or dissipation modules are required.
Does CPT replace boreholes under Eurocode 7?
CPT provides continuous profiles of soil behaviour type and strength, but Eurocode 7 requires direct identification and sampling for design parameters. On most Reading projects we combine CPT soundings with a reduced number of boreholes or test pits to recover samples for lab testing and to verify the CPT-derived classification. This hybrid approach satisfies BS EN 1997-2 while cutting programme time.
