CBR testing in Bristol.

Same-day and next-day dates are often available, subject to the schedule, but Bristol is around two hours from our laboratory in Milton Keynes, so next-day is the more realistic of the two. The M4 and M5 make Avonmouth, Filton and Emersons Green easy to reach. We do not guarantee an attendance time. Ring 0117 422 8206 with the postcode and the number of positions and we will offer the earliest date we have.

Rarely on the natural ground. The estuarine clay and peat are so soft that the CBR is at or below the bottom of the usable range, and the design does not rely on it. Access roads and yards there sit on a designed granular layer, often over a geotextile or geogrid. The useful tests are plate bearing on that layer, with a derived CBR if the specification asks for one, and a DCP profile to see what lies beneath.

It depends on moisture more than anything. Freshly trimmed and dry, the weathered red mudstone can give a good in-situ value. After rain and site traffic the surface softens quickly, and soaked laboratory values are commonly in the low single figures. Designers at Hengrove, Whitchurch, Yate and Emersons Green normally work to the soaked figure and allow a capping layer.

The Lias is alternating clay and thin limestone bands. One plunger position sits on weathered clay and the next, a few metres away, on a limestone band just below the surface, and the two values can differ several times over. Neither is wrong. Spread the positions, log what each one is sitting on, and let the designer work to the weaker material where the road crosses both.

Usually not. At Clifton, the Downs and along the limestone ridges, intact rock at formation level is far stronger than any CBR requirement and the plunger cannot test it anyway. The thing to check is what fills the gaps. Rockhead is uneven, with clay-filled fissures and pockets of softer cover, and those soft pockets are where a CBR or plate test is worth placing.

Send us the clause or tell us what the number is for. Adoptable estate roads normally need an in-situ CBR at formation level, often with a soaked laboratory CBR for the design value. Yards and access roads on granular platforms are more often checked by plate bearing with a derived CBR. The three are different measurements, and the report should say which one was used.

Only where the material suits the plunger, which means a maximum particle size of around 20 mm. Fine spoil and ashy fill can be tested. Rubble, dock fill and coarse colliery waste cannot be tested reliably, and plate bearing is the better method. On any fill, expect results to vary sharply between positions and allow for more of them.

Yes, significantly on the mudstone and the Lias clay. CBR is strongly influenced by moisture content and a result describes the formation on the day it was tested. Bristol gets a good deal of rain off the Severn, so test soon after trimming, protect the formation afterwards, and use a soaked laboratory CBR where the design has to allow for the wettest likely condition.

The specification or the adopting highway authority sets the number. Where they are silent, it depends on the length of road and how variable the ground is, and Bristol ground is more variable than most. Positions are spread along the formation and 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 goes back to the laboratory in Milton Keynes with the technician, or you can courier one. 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. Confirm the sample size with us first.

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 needs an accredited result, name the CBR method when you enquire and we will confirm whether it is on the schedule, and whether the report will carry the UKAS mark, before you book.

Every visit is quoted from the site postcode, and at two hours each way travel is a real part of the price. Grouping all your CBR positions, any plate tests and any sampling into one visit is far better value than separate trips, and we try to combine Bristol work with other visits along the M4 and M5. Standby time, restricted access and out-of-hours working add to it.

No. Hixtra has one laboratory, in Milton Keynes, and every Bristol visit is run from there. The 0117 number rings through to the same team as our other numbers, and we keep no staff, vehicles or depot in the city. Coverage means we come to you. Book with a firm ready date and have the formation trimmed when we arrive, so the trip is not wasted.