CBR testing in London.

Same-day and next-day dates are often available, subject to the schedule. We do not guarantee an attendance time, and in London the M1, the M25 and the roads inside the North Circular decide the arrival time more than the distance from our laboratory in Milton Keynes. Early starts help, and so does grouping positions. Ring 020 7993 5733 with the postcode and we will offer the earliest date we have.

Low, and lower when wet. London Clay is a high plasticity clay, and soaked laboratory values are commonly in the low single figures. A dry-day in-situ test on a freshly trimmed formation often reads higher, which is why it should be treated as an upper bound. Most specifications on the clay assume the wet case, call for a capping layer and ask for the testing on that.

Probably the gravel. The River Terrace Deposits along the Thames corridor and the Lea valley are sands and gravels that give far better CBR values than the clay beneath them, and their edge does not follow site boundaries. Two positions a short distance apart can be on different materials. Check the ground investigation, log what each test position is sitting on, and do not apply one design CBR across both.

Where the material is fine enough. The plunger suits material up to about 20 mm, so ash and sandy fill can be tested, but demolition rubble, crushed concrete and old foundations cannot be tested reliably. Made ground is also the usual reason results scatter on London sites. Allow for more positions, and where the fill is coarse, plate bearing with a derived CBR is the better route.

Send us the clause or tell us what the result is for. Adoptable roads and highway schemes normally need an in-situ CBR at formation, often with a soaked laboratory CBR for design. Car parks and yards on capping are more often checked by plate bearing with a derived CBR. They are different measurements and should be labelled as such in the report.

No. Crane hardstandings and piling platforms are designed to a bearing pressure, and the check is a plate bearing test on the finished platform at the positions the outriggers or tracks will load. CBR is a pavement design parameter. If the site needs both, a road formation and a crane pad, we can do both on the same visit.

The equipment is vehicle mounted and reacts against the weight of the vehicle, so it needs a route to each position and room to stand over it. Tell us about gate widths, basement edges, banksman requirements, ULEZ and congestion charge zones, restricted delivery hours and any possession windows. The test level must be exposed and trimmed flat. The plunger hole is backfilled before we leave.

Yes, more than almost anything else. CBR is strongly influenced by moisture content, and London Clay at formation softens quickly under rain and plant. A result describes the formation on the day it was tested. Test soon after trimming, blind or cover the formation afterwards, and rely on a soaked laboratory CBR where the design has to allow for the wettest likely condition.

Your specification or the adopting authority sets the number. Where they are silent, it depends on the area and how variable the ground is, and on sites that cross from clay to gravel or onto fill, more positions are needed to show it. Each test is made at the level the design relates to. In-situ testing is commonly carried out in accordance with BS 1377-9.

Yes. We take a bulk disturbed sample at formation level while we are on site and it travels back to the laboratory with the technician, or you can courier one to Milton Keynes. The specimen is remoulded into a 152 mm mould at the specified compaction and moisture condition, soaked where required, and tested under surcharge discs, commonly to BS 1377-2.

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, the borough or your client’s engineer 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 how long the visit takes, and in London time on site is driven by access. Road charges, restricted hours, standby while an area is handed over and night or weekend working all add to it. Grouping positions so the vehicle moves as little as possible keeps the cost down.

No. There is no Hixtra office in London. The 020 number rings through to the laboratory in Milton Keynes and every team travels from there. Coverage means we attend, not that we keep staff or kit in the borough. Samples for laboratory CBR go back to Milton Keynes with the team or by courier.