Earthworks testing

What does an earthworks testing programme usually include?

It falls into two halves: classification testing to establish what the material is and whether it can be used, and control testing during placement to confirm it has been compacted as specified. Classification typically covers grading, plasticity, moisture content and Moisture Condition Value, sometimes with CBR, shear strength and chemical tests. Control testing is mostly in-situ density and moisture, run layer by layer as cut and fill, bunds and engineered layers are built up.

Which specification is UK earthworks testing usually carried out to?

On highways and most major infrastructure work it is Series 600 of the Specification for Highway Works. Series 600 sorts fill into classes covering general granular and general cohesive fill, selected granular and cohesive fill and stabilised material, and sets the acceptability requirements for each in its material table. The individual test methods it calls up are largely BS 1377 methods, with the project-specific limits and testing frequencies written into the contract appendices.

What is the difference between method compaction and end-product compaction?

Method compaction specifies how the material is placed; end-product compaction specifies what the finished layer has to achieve. Under method compaction the specification sets the plant category, the maximum layer depth and the minimum number of passes for each material class, so compliance is demonstrated by the placing record. Under end-product compaction the field dry density has to reach a stated percentage of a laboratory maximum dry density, which means density testing on every layer.

What testing do we need before using site-won material or a borrow pit?

Enough to assign the material to a class and confirm it meets the acceptability requirements for the use you have in mind. That normally means grading, plasticity, moisture content and a Moisture Condition Value, plus a laboratory compaction test to establish maximum dry density and optimum moisture content, with chemical testing where sulfate or organic content matters. Test each distinct material separately rather than averaging across a mixed stockpile or a deep face.

What is Moisture Condition Value testing used for on an earthworks site?

MCV is used as a fast suitability check on whether material is dry enough to place and compact. It measures the compactive effort needed to bring a sample close to full compaction, and the result is available in minutes rather than waiting overnight for an oven-dried moisture content. The acceptable range is set in the specification for each material class, and calibrating MCV against moisture content for that material makes the site readings far more useful.

Do we need a compaction trial before the main filling starts?

You need one if you intend to use plant or a layer thickness the specification does not already cover. Series 600 allows plant and methods outside its own compaction table only where the contractor demonstrates at site trials that the alternative achieves an equivalent state of compaction. A trial is also worth doing voluntarily on an unfamiliar material, because it settles layer thickness and pass count before there is a whole embankment to argue about.

How often does testing need to be carried out through a fill programme?

The frequency is set by the contract rather than by the test standard. On Series 600 jobs it is written into the contract-specific appendix, typically as a rate per layer, per area or per volume of material placed, and it applies separately to each material type. Expect the rate to tighten when the material changes, after a failure, when a new borrow area opens or when the weather has affected placing conditions.

What happens to the testing programme in wet weather or over the winter?

Testing usually increases rather than stops, because moisture is what governs whether material stays acceptable. Cohesive fill wet of optimum will not reach the required density however much it is rolled, so MCV and moisture checks become the daily control, and material that was acceptable in September can be unacceptable in January. Stabilisation is more restricted still: lime and cement specifications normally set a seasonal window and a minimum temperature for the works.

Who receives the results, and how quickly are they needed to release a layer?

Results normally go to whoever is signing the layer off, usually the site engineer or the client's representative, with a copy to whoever instructed the testing. Because filling often cannot continue until the layer below is accepted, field density and moisture results are commonly wanted the same day or the next morning. Tell us who needs the report and to what deadline and we will confirm the expected timing before the work is booked.

Would a site laboratory be worth it on our earthworks contract?

It usually is once the daily testing volume is high enough that travelling to site for each round of tests becomes the constraint. A project laboratory suits sustained fill programmes where moisture contents, MCV and density results are needed the same day to release layers and keep plant working. Below that, scheduled visits from the regional team are normally more economical. Send us the programme and expected volumes and we will advise which makes sense.

Our earthworks specification asks for accredited testing. How do we confirm what you can cover?

Send us the specification or testing schedule and we will go through it method by method. Hixtra holds UKAS accreditation to ISO/IEC 17025 for the tests listed in its schedule of accreditation, number 8996, and accreditation is specific to the listed methods and scope rather than to a service as a whole. Where part of a programme sits outside that scope we will say so before work starts, not at reporting stage.

How do we get an earthworks testing programme priced?

Send the site postcode, the earthworks specification and testing schedule, the fill classes involved, the expected volumes and the construction sequence. Cost across a programme is driven mainly by the number of visits and test positions, the split between laboratory and site work, travel, and any standby or out-of-hours working. An outline programme gives a far more useful price than a list of test names, and preferred dates let us confirm availability.