Testing for site investigations

What testing do you provide in support of a ground investigation?

Laboratory testing of soils and aggregates, together with field testing on site through our technicians. That typically covers classification work such as moisture content, plasticity and particle size distribution, particle density, compaction and moisture condition value testing, laboratory CBR, shear strength and soaking or swelling tests, plus in-situ methods where the investigation calls for them. Specifications commonly name BS 1377 methods, and increasingly the BS EN ISO 17892 series for geotechnical laboratory testing.

Can you carry out the boreholes and trial pits as well?

No. This service is testing support rather than a full intrusive investigation package, so the drilling, trial pitting, logging and the interpretative report stay with your investigation contractor and geotechnical adviser. We test the samples they recover and attend site for field testing where that is scheduled. The split is worth confirming early, because an investigation budget that assumes the laboratory is also doing the fieldwork will not add up.

Can you send technicians to site during the investigation?

Yes, our technicians attend site for field testing scheduled as part of an investigation. That commonly means in-situ CBR, plate bearing, DCP, LWD and in-situ density and moisture measurements, carried out at formation, in trial pit bases or across the areas being assessed. Attendance is planned against the investigation programme, since a trial pit is only open for a short time and a test position has to be reached before it is backfilled.

What does our investigation contractor need to send with the samples?

The samples with a schedule of the testing required, plus the exploratory hole references, depths, sample type and a description of the material. Borehole and trial pit logs are the single most useful thing to send, because they let us check that the sample type and quantity actually suit the scheduled tests. Confirm who is instructing the work and who results are issued to before the first delivery arrives.

How do we know a sample is good enough for the test we want?

It depends on how the sample was taken, not simply how much of it there is. BS EN ISO 22475-1 sets out sampling categories A, B and C and sample quality classes 1 to 5, and strength and stiffness testing needs the least disturbed classes while classification and compaction work can run on disturbed bulk samples. A bag of arisings will give you a grading and a plasticity index but not an undisturbed strength.

How do you schedule laboratory tests from borehole and trial pit logs?

Testing is scheduled by stratum and depth rather than by hole, so each material the investigation identified is represented across the site. Classification testing is usually scheduled first and more widely, with strength, compaction and CBR work targeted at the horizons that matter to the design. The selection is your geotechnical adviser's decision, and we'll flag where a scheduled test does not suit the sample actually recovered at that depth.

What happens if there isn't enough material for everything scheduled?

We tell you before testing starts and agree what takes priority, rather than working down the list until the sample runs out. Some tests consume the specimen, so the order they are carried out in can decide what remains possible afterwards. Where the shortfall matters, the options are to trim the schedule, substitute a sample from a nearby depth or resample, and resampling usually means returning to a hole that has already been backfilled.

Can testing start before the investigation is finished?

Yes, and on a programme under pressure it usually should. Sending samples in batches as holes are completed keeps the laboratory working while fieldwork continues, instead of everything arriving on the last day. Classification results can then be released early to support the ground model while longer tests run on. Tell us the reporting deadline at the outset and we'll sequence the schedule around it.

How long does laboratory testing take on an investigation programme?

It varies by method, and conditioning drives the longer items rather than the testing itself. Classification work is comparatively quick; compaction, CBR and anything needing soaking, saturation or staged loading requires preparation time that cannot be shortened. There is no single turnaround for every method, so we confirm the expected timing for the scheduled tests before the work is booked and can prioritise the results your programme needs first.

Can you supply the results in AGS format?

Yes. Laboratory results can be issued in the AGS data transfer format alongside the reports, so they load into your geotechnical database and interpretative software without retyping. Hixtra is an AGS member. Confirm the AGS version your project requires and the conventions for hole and sample references at the start, because mismatched references cause more trouble at import than the data itself.

Is geotechnical laboratory testing for an investigation UKAS accredited?

Some methods are and some are not, which is why the schedule matters more than the logo. Hixtra holds UKAS accreditation to ISO/IEC 17025 for the tests listed in its schedule of accreditation, number 8996. Accreditation is specific to the listed methods and scope. Investigation specifications often require accredited results for named tests, so ask us to confirm the status of each one against your schedule before testing is instructed.

What do you need to quote for testing on a site investigation?

Send the testing schedule with the number of tests by method, the site postcode, whether samples are being delivered or need collecting, and the date results are needed. Cost is driven by the number of specimens, the preparation each method needs, any soaking or conditioning, the reporting format and whether field attendance is included. If the schedule is still being drafted, send the draft and we'll comment on what is practical.