A few years back, we were called to a distribution centre job off the A449 near Fordhouses. The contractor had laid a rigid pavement over what looked like decent ground, but within eighteen months the joints were faulting and the slabs had cracked. Core drilling revealed the issue wasn't the concrete mix - it was the subgrade. Wolverhampton sits on a complex transition between Mercia Mudstone and superficial glaciofluvial deposits; the stiffness can vary dramatically across a single site. Before you specify slab thickness or reinforcement, you need a reliable picture of the ground. Combining a CBR road assessment with targeted boreholes gives us the modulus values that feed directly into the pavement design, avoiding the costly guesswork that leads to early failure.
In Wolverhampton, a rigid pavement is only as good as its subgrade. You can't engineer the slab in isolation from the ground it sits on.
Method and coverage
Regional considerations
Wolverhampton's population of over 260,000 relies on infrastructure built across a landscape scarred by centuries of shallow coal mining. The Black Country's industrial past means we are constantly designing pavements over unrecorded bell pits or backfilled shafts less than 10 metres deep. The risk isn't always obvious on a desk study. A rigid pavement, being a monolithic structure, can bridge very small voids, but differential settlement exceeding 5 mm will induce tensile stresses the concrete can't handle. We've seen industrial yards where a single slab collapsed because of a decaying timber headframe five metres below. Our site investigations therefore don't stop at the subgrade; we routinely specify probing or geophysics to rule out mine workings before the pavement design is finalised, and we tie the slab design into a ground treatment strategy where necessary.
Process video
Standards that apply
BS EN 13877-1:2013 (Concrete pavements), I. D. 76-06 (DMRB for rigid pavements), BS 8500-1:2015 (Concrete specification), Eurocode 7 (BS EN 1997-1:2004 for geotechnical design), Specification for Highway Works (MCHW 1)
Complementary services
Subgrade Characterisation for Concrete Pavements
A combination of dynamic cone penetrometer (DCP) profiling, in-situ density testing, and laboratory resilient modulus determination. We map the spatial variability of the formation layer to define zones of uniform design, a critical step on Wolverhampton's mixed glacial deposits.
Mine Workings Assessment and Ground Treatment Design
Given the high risk of shallow coal workings in the region, we integrate rotary drilling with downhole camera inspection to identify voids. Where treatment is needed, we design grouting programmes that stabilise the ground before the pavement subbase is placed, ensuring long-term slab support.
Typical parameters
Top questions
What is the typical cost for a rigid pavement ground investigation in Wolverhampton?
For a standard industrial unit or access road in the Wolverhampton area, a ground investigation tailored to rigid pavement design typically falls between £1,500 and £4,240. The final figure depends on the number of exploratory holes, the depth required to check for mine workings, and the extent of laboratory testing needed to determine resilient modulus and sulphate class for the concrete specification.
How do you account for historical mining when designing a concrete pavement in the Black Country?
We start with a detailed coal authority mining report and BGS geological mapping, but we never rely solely on records. We physically probe the ground with a combination of rotary open-hole drilling and, where the risk is high, geophysical surveys like microgravity. If voids or loose backfill are found, the pavement design incorporates a grouting phase to consolidate the ground, and the slab may be detailed with heavier reinforcement to provide some bridging capacity over any residual settlement.
Which joints are most suitable for heavy industrial rigid pavements?
For heavily loaded yards, such as those serving waste transfer stations or steel stockholders, we often steer clients towards steel fibre-reinforced slabs with sawn contraction joints at 6-metre centres. The fibre reinforcement controls micro-cracking and improves post-crack behaviour. At the joints, we specify round dowels with a debonding compound to allow horizontal movement, and we pay close attention to the joint sealant to prevent aggregate interlock loss under constant turning loads.
What is the minimum CBR value you recommend for a rigid pavement subgrade in Wolverhampton?
While rigid pavements are less sensitive to subgrade CBR than flexible ones, we target a minimum CBR of 5% at formation level. In Wolverhampton's clay-rich Mercia Mudstone areas, we often find values dipping to 2-3%. In those cases, we don't simply thicken the slab; we stabilise the upper 350 mm with lime to modify the plasticity and improve the long-term stiffness, verified by CBR testing after treatment and before the subbase goes down.