CBR testing in Winchester.

Same-day and next-day dates are often available, subject to the schedule. We never guarantee an attendance time, but Winchester is a reasonable run from our laboratory in Milton Keynes down the A34 and M3, so dates are usually easier to find here than in the far south west or the north. On chalk, speed matters. Ring 01962 461501 before the formation is trimmed, not after it has stood open for a week.

Because chalk changes once it is exposed. Freshly cut and dry, intact chalk gives a high CBR. After rain, frost or repeated trafficking the surface degrades to putty chalk, and the same formation can return a fraction of the value. We ask when it was exposed, whether it has rained since and what has run over it. Test soon after exposure, then cover the formation promptly.

They spoil it. A CBR plunger is only 50 mm across, so if it seats on a flint the reading is far too high, or the test refuses altogether. We log those positions and move a short distance to retest. On very flinty chalk, or on Clay-with-Flints with a lot of stone, a plate bearing test loads a much larger area and gives a more representative answer.

Treat it as a clay. Clay-with-Flints caps much of the higher ground around Winchester in variable thickness. It is moisture sensitive, gives much lower values than the chalk beneath it, and softens quickly when wet. A scheme can cross from chalk to clay and back in a few hundred metres, so make sure each material is tested and do not apply the chalk value to the clay lengths.

We can, but the natural ground there is alluvium, peat and tufa with groundwater at shallow depth, and the CBR is very low. Roads and hardstandings on the valley floor are designed over that ground on a granular layer, and the useful tests are plate bearing and density on the layer. Tell us what the designer has asked for and we will match the testing to it.

Send us the clause. Adoptable estate roads normally need an in-situ CBR at formation level. On chalk, some designers prefer plate bearing with a derived CBR, because flints trouble the plunger less. A laboratory CBR on remoulded chalk reads lower than the intact formation, so check what your engineer wants. The report should always say which method produced the number.

It is a conservative one. To prepare the specimen the chalk is broken down and recompacted into a 152 mm mould, which destroys the natural structure that gives intact chalk its strength. That is appropriate where the chalk will be excavated and placed as fill, and pessimistic for an undisturbed formation. Testing is commonly carried out to BS 1377-2. Tell us which case applies and we will advise.

The specification or the adopting highway authority sets the number. Where they are silent, it depends on the length of road and how many times it crosses from chalk to clay cover or into a dry valley, where looser head and chalk wash collect. Positions are spread so that the weaker lengths are found. In-situ testing is commonly carried out in accordance with BS 1377-9.

No. Where clay cover sits on chalk, water can dissolve pipes and hollows beneath it, and they can be metres deep. A CBR plunger stresses only the top of the formation and will not find them. That is a question for the ground investigation and the designer. CBR testing describes the surface the road will be built on.

The test level exposed and trimmed flat, safe vehicle access to each position and a clear working area. The equipment is vehicle mounted and reacts against the weight of the vehicle, so steep downland gradients and very soft valley ground can rule a position out. Keep traffic off the formation before we arrive. The plunger hole is backfilled before we leave.

Hixtra holds UKAS accreditation to ISO/IEC 17025 under schedule number 8996. Accreditation is granted method by method, not to the company as a whole, so it applies only to the tests listed on our current schedule. Most of our soil tests are on it. If your specification or the adopting authority requires an accredited result, name the CBR method when you enquire and we will confirm whether it is on the schedule before you book.

Every visit is quoted from the site postcode. The price depends mainly on the number of positions and the time on site. Repeat visits are what push the cost up on chalk, usually because the formation was not ready or had degraded before we arrived, so book with a firm date. We can often combine a Winchester visit with work in Southampton, Eastleigh or Basingstoke.

No. There is no Hixtra office in Winchester or anywhere in Hampshire. The 01962 number rings through to the laboratory in Milton Keynes and every team travels from there. Coverage means we attend. It does not mean staff, vehicles or kit are kept locally. Samples for laboratory CBR travel back to the laboratory with the team.