Geotechnical Laboratory Testing
Our laboratory routinely performs geotechnical testing on samples obtained from its own ground investigations, but also other consultants, developers, builders and house owners.
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Laboratory Test Types & Pricing
Laboratory testing regularly carried out by iGeo typically includes:
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Water Content testing
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£5+vat per sample
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Used to assess the water content of the soils at the current time. These test results may be used in conjunction with other tests, such as volume change potential test or compaction tests​
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Soil strength
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£40+vat per sample​
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using quick undrained or multistage triaxial tests in cohesive soils on undisturbed U100 or U38 samples)
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Wet sieve analysis
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£28+vat per sample
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for coarse grained soils, or to establish the potentially shrinkable silt and clay component
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Volume change potential [Atterbergs / Liquid & Plastic Limit / shrinkage testing]
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£28+vat per sample when the sample is a clean clay without any gravel, including fine gravel
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£42+vat if any gravel is present
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to obtain the soils volume change potential / plasticity index
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Water soluble sulfates
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£28+vat​
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to assess the levels of soluble Sulfates currently present in the soils
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Other testing, we are able to carry out include:
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Particle size analysis
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£56+vat - by hydrometer, including wet sieve testing
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for finer grained or mixed soils including the silt and clay percentages
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Loss on ignition organic contents
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​£26+vat
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to assess the soil organic content, which may influence strength, compressibility & gassing potential
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Saturation Moisture Content of Chalk
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£26+vat​
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to assess the chalk clasts density which can be relevant to its mass strength & dissolution susceptibility
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Compaction tests
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Cost vary - prices on application
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to determine the optimum moisture content and maximum dry density of the samples, used in earthworks design
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Note: We have a minimum testing charge of £90+vat
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Where possible, as standard we aim to complete tests in 10 working day turnaround, however as the laboratory workload fluctuates, sometimes the turnaround can time can increase significantly.
It is sometimes possible for us to offer an accelerated turnaround testing time, which is subject to a surcharge over the total testing charge (including the minimum charge):
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3 working day* - 100% surcharge
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5 working day* - 50% surcharge
* subject to availability in the laboratory
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Please call if you would like to know our curent standard turnaround times, or if accelerated turnaround is required.
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On completion of the testing an invoice would be emailed to the client from QuickBooks, which can be paid by bank transfer or online via debit/credit card or PayPal. iGeo would then release the results on receipt of payment.​​​​​​​​​
​​​​​​​​​Taking of Samples
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Building control and warranty providers often ask builders, developers, and house owners for soil test results when they are in the process of excavating foundations. This is often, but not exclusively to determine how shrinkable the soils are (its volume change potential). Normally this is due to the proximity of trees. Foundations depths can be influenced significantly due to the trees surrounding the plot or site depending on the volume change potential of the materials.
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Samples are often taken by the client, builder or consultant and are delivered to our laboratory for shrinkage / volume change potential testing. The number of samples required and depths they are taken from is often stipulated by the project's structural engineer, building control or warrantee provider. We would report just the test results for the samples received, however in the absence of sampling guidance.
We may be able to provide some informal sampling advice (without liability attached) purely for volume change potential testing.
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Clean samples of virgin soils (free of material which has collapsed in to the hole) should be taken and placed in sealed plastic bags (zip lock bags or using a cable tie).
The bags should be labelled with the Site Name, also the trial pit or hole number reference and sample depth (e.g. TP1 / 1.0m, Front / 1.5m, or A / 2.0m, etc)
For shrinkage/volume change potential assessment, the sample size should be 2kg for clays or sands (about ½ a supermarket carrier bag full), or 10kg for medium grained gravels.
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Note: Strength tests are only possible on undisturbed samples taken with a bespoke sampling tube. It is not possible to carry out strength testing on disturbed samples, unless reconstituted samples are used. Reconstituted sample testing may result in inaccurate results returned.
The samples should be representative of the soils across the foundation footprints, also with depth. In terms of sampling depth, this should reflect the likely range of depths possible, dependant on the soils volume change potential, also the proximity and species of trees (all existing, removed, or proposed trees within their zone of influence). ​
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Further representative samples may be required if the materials change across the site or with depth.
Shallow samples may be required to assess the volume change potential for suspended ground floor slabs, compressible membranes etc.
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An appropriate number of sampling locations would be required to have confidence that the soil samples tested are representative across the proposed foundation footprint(s). For example, a single sampling location may be suitable for a small extension, whereas at two or more sampling locations may be required larger extensions, more if the soils differed between locations. At least three sampling locations would be suggested for a small new dwelling, with more locations required for larger houses or again where soils differed.
In all cases, we would suggest that more than one sample should be tested to give more confidence of the volume change potential (shrinkage) of the soils.
The more samples that are tested, increases the reliability for the structural engineer in preparing their foundation design .
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Soils which contain organic matter, brick or other man-made fragments (fill or made ground) would not be suitable materials to be founded on, therefore these materials should be bypassed to virgin soils below. The depth to the base of fill or made ground should be recorded, passing this information on the structural engineer, warrantee provider or builder, along with any relevant photos.​
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iGeo Ltd can provide geotechnical engineers for trial pitting and borehole ground investigations, and are also able to provide a tree table report based on laboratory testing on samples delivered to us (at additional cost).
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A tree table report would provide NHBC Chapter 4.2 calculated foundation depths at intervals away from the tree species supplied to us by the client based on the volume change potential of the soils tested. It is assumed that the tree species given include all existing, removed or proposed trees within their zone of influence.​
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The tree table report would also summarise other relevant recommendations from the NHBC Standards Chapter 4.2, based on the soils volume change potential. This would include the Radon protection level for the site based on its post code using BRE Report BR211:2015.​
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​​​​​​​​​​​​Notes /Caveats
​Taking and testing of samples delivered to our laboratory does not constitute a ground investigation, if we were carrying out a ground investigation, a geotechnical engineer would attend site to log the soils and sample from the trial pits or boreholes, taking representative samples relevant to the proposed construction, the ground conditions, soil strength, water ingress, trees present etc, for lab testing and providing a geotechnical report.
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Where you have been asked by others to take samples yourself, in order to prevent samples being taken at inappropriately shallow depths (~1m) where trees are/have been in the area and shrinkable soils may be present, we may be able to provide some informal sampling advice. Any advice given should be treated as rough general guidance only, without liability attached, as to the approximate depths suggested for you to take representative samples from, and deliver to us purely for volume change potential testing.
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For information, in a high volume change potential soil, some high water demand trees have the potential to affect 1.0m deep foundations up to 35m away.
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iGeo Ltd takes no responsibility for informal advice or for the samples taken by the client, as the samples may not be representative, important layers or information may be missed, also there are a number of other factors which can influence proposed foundation & depths, some of which can’t be assessed by samples delivered to us for testing.
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The testing assumes the samples are fully representative of the soils across the site, both vertically and laterally. The overall responsibility for the materials sampled, also the sampling locations and depths, would be down to the client and/or clients representative.
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Unless otherwise agreed, it is assumed that your structural engineer will calculate foundation depths based on the results of the volume change potential testing and proximity of reported trees . Your structural engineer would require a complete list of trees (existing, proposed and removed), including species, location & untrimmed height if removed.
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Although we will look for man-made materials within the samples delivered, we may not be able to establish if the samples are natural soils or made ground.
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We cannot test or give any recommendations regarding soil strength, excavation instability, water ingress issues, soakaway design, or other ground stability issues such as ground dissolution, landslips, etc from samples which are delivered to us.​​