In Bedford, we see a lot of projects where the pavement design gets the concrete strength right but the ground support wrong. That mismatch shows up fast. The Oxford Clay Formation under much of the town is stiff overconsolidated clay. It holds up well in summer. It swells in winter. If you do not account for that seasonal volume change, your rigid pavement will crack at the joints within the first two years. Our approach puts the subgrade first. We run a site investigation under BS 5930 to characterise the clay. We pull undisturbed samples for swell testing and CBR. Then we size the slab thickness, joint spacing, and base course to work with the ground, not against it. For highway schemes near the A421, we often combine this with a CBR road assessment to verify the formation strength before the concrete goes down. On industrial yards we also look at flexible pavement options where heavy turning loads might make a composite section more practical.
The subgrade is half the pavement. Get that wrong and the concrete will tell you within two years.
Methodology applied in Bedford
Risks and considerations in Bedford
We were called to a distribution centre off the A6 where the yard pavement had cracked at every third joint within 18 months. The original design assumed uniform ground. The site investigation had three boreholes for two hectares. That missed a band of soft alluvium running diagonally across the yard. The slab was 200 mm unreinforced concrete on 150 mm of Type 1. On the gravel side it performed fine. On the clay side the joints opened up and the slabs rocked under forklift loads. Water got in. Pumping started. The fix cost more than the original pavement. We see this pattern often. The risk is not the concrete mix. It is the ground variability. In Bedford the river terrace deposits and floodplain clays inter-finger in ways that a sparse investigation will not catch. A proper rigid pavement design needs enough exploratory points to map those boundaries. It also needs a drainage plan. Standing water on the subgrade softens the clay and accelerates failure.
Our services
We offer a full pavement design package tailored to Bedford ground conditions. Each service ties back to the site investigation data.
Subgrade investigation and CBR testing
We sample the Oxford Clay and river gravels at close spacing. Laboratory CBR and swell tests give us the design parameters for the slab.
Rigid pavement thickness design
Using Westergaard analysis and TRL 637 we calculate the required slab thickness, joint layout, and reinforcement for the traffic loading.
Joint and dowel specification
We detail the contraction and expansion joints. Dowel diameter and spacing are calculated from the predicted slab movement and load transfer requirements.
Construction quality control
We test the concrete flexural strength at 7 and 28 days. We check the base course compaction and the subgrade moisture content before the pour.
Frequently asked questions
How deep should the subgrade investigation go for a rigid pavement in Bedford?
We typically investigate to at least 2 metres below the formation level. The Oxford Clay can have a weathered crust that looks stiff but softens quickly. We need to see what is underneath.
What is the cost range for a rigid pavement design for a Bedford industrial yard?
For a typical industrial yard design including site investigation, CBR testing, and the pavement design report, the fee ranges from £1,630 to £5,020 depending on the yard area and the number of exploratory points needed.
Do you use reinforced or unreinforced concrete for rigid pavements?
It depends on the joint spacing and the ground. For joint spacings under 5 metres on stiff ground we often use unreinforced concrete. On softer or variable ground we may add mesh or steel fibres to control cracking.
How do you handle the transition between rigid and flexible pavement sections?
We design a transition slab or a butt joint with a thickened edge. The key is to manage the differential stiffness so you do not get a bump at the interface under repeated loading.
What concrete specification do you recommend for heavy forklift traffic?
We specify a C32/40 concrete with a minimum flexural strength of 4.5 MPa at 28 days. The aggregate type matters for wear resistance. For very heavy point loads we may go to C40/50.