CBR testing in Birmingham.

Same-day and next-day dates are often available, subject to the schedule. Birmingham is about an hour and a half from our laboratory in Milton Keynes by the M1 and M6 or the A5 and M6 Toll, and Solihull, Tamworth, Redditch and Lichfield are much the same. We do not guarantee an attendance time. City centre sites need a little more planning around access and delivery hours, so tell us about those when you ring 0121 270 6622.

Sometimes. The in-situ plunger method suits material with a maximum particle size of around 20 mm. On a sandy or ashy fill it can work. On brick rubble, slag or crushed concrete the plunger lands on a hard fragment or in a void beside one and the number means little. There a plate bearing test, which loads a much larger area, is normally the right call, with a derived CBR reported if your specification allows it.

It depends heavily on moisture. Freshly trimmed and dry, weathered Mercia Mudstone can give a respectable in-situ CBR. Once it has been rained on and trafficked the surface softens and the value drops sharply, and soaked laboratory values are commonly in the low single figures. That is why designers on the east side of the city and around Solihull normally work to the soaked figure and specify a capping layer.

Sherwood Sandstone under the west of the city weathers to a dense sand that drains freely, so its strength changes little with the weather and CBR values are higher and more consistent. The catch is the fault line. A scheme near the centre can cross from sandstone to mudstone within the site boundary, so check which one each test position is on before a single design CBR is applied to the whole road.

Send us the clause or tell us what the result is for. For adoptable estate roads it is normally an in-situ CBR at formation, often with a soaked laboratory CBR for design. For yards and hardstandings on fill it is more often plate bearing with a derived CBR. The three methods are not interchangeable, and a report should always say which one produced the number.

Your specification or the adopting authority sets the number. Where they are silent, it comes down to the area and how variable the ground is, and on Birmingham fill that means more positions, not fewer. We choose positions to represent the scheme, suspect areas included, not to find the best spot. In-situ testing is commonly carried out in accordance with BS 1377-9.

Yes. CBR is strongly influenced by moisture content. On Mercia Mudstone and glacial till a formation left open over a wet weekend is a different material on Monday morning, and the result will show it. Test soon after trimming, protect the formation afterwards, and where the design has to cover the wettest likely condition use a soaked laboratory CBR instead of waiting for a dry day.

Yes. We take a bulk disturbed sample at formation level during the site visit and it travels back to the laboratory with the technician, or you can courier one. The specimen is remoulded into a 152 mm mould at the compaction and moisture condition the specification calls for, soaked where required, and tested under surcharge discs. Testing is commonly carried out to BS 1377-2. Ask us how much material we need before you dig.

No. A CBR plunger stresses only the top few hundred millimetres of the formation. Across the Black Country, around Tamworth and on parts of the South Staffordshire coalfield, shallow workings are a question for the Coal Authority mining report and the ground investigation. CBR testing describes the surface the road will be built on and nothing below it.

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 very soft ground, steep gradients or positions hemmed in by existing structures can rule a location out. Tell us about induction, permits and any Clean Air Zone or delivery hour restrictions. 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, the highway authority or your client’s engineer needs an accredited result, tell us which CBR method you need 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. Excavating to test level, restricted access, standby while an area is handed over and out-of-hours working all add to it. Grouping a Black Country site and a Birmingham site into one day keeps travel down. Send the postcode, the number of positions and your dates and we will quote.

No. Hixtra has one laboratory, in Milton Keynes, and every Birmingham visit is run from there. The 0121 number rings through to the same team as our other numbers, and we do not keep staff, vehicles or a depot in the city. The region is central and well connected, so the drive is well within a normal working day and we can often combine several West Midlands visits in one trip.