LWD testing in Milton Keynes.

Same-day and next-day dates are often available, subject to the schedule, and they are easier to find here than anywhere else, because the laboratory is in the city and an LWD visit needs only a technician and portable equipment. We still do not guarantee an attendance time. Ring 01908 505833 and we will tell you what the day looks like.

A lightweight deflectometer measures how stiff the layer under the plate is, by dropping a known weight onto the plate and recording the deflection of the surface. A 10 kg weight falling onto a 300 mm plate is typical, with a few seating drops to bed the plate followed by measuring drops that are averaged. The result is a dynamic surface modulus in megapascals, calculated from the force applied and the deflection it produced. On a warehouse sub-base that means a reading every few minutes across the whole footprint.

Yes, and locally it is practical. Because we are minutes away, a technician can test the capping when it is compacted, come back for the sub-base, and return again if an area has to be reworked, without the travel cost that makes repeat visits expensive elsewhere. Testing layer by layer finds a soft area while it is still cheap to fix.

Not reliably once it is wet. Oxford Clay at formation deforms plastically and gives little elastic recovery for the equipment to read, so results scatter. At formation level a CBR, with a soaked laboratory CBR for the design value, is the right approach. The LWD belongs on the capping and sub-base above.

Your specification or designer sets it. For pavements, DMRB CD 225 defines foundation classes by surface modulus, starting at 50 MPa, and the specification says which class applies and how it must be demonstrated. For warehouse floor slabs the engineer normally sets a project value for the sub-base. Tell us the target and the report shows each position against it.

Your specification may set a grid. Where it is silent, the aim is to cover the footprint closely enough that a soft area cannot hide between positions. Each test takes a few minutes, so dozens in a visit is normal. Send the slab layout and we will suggest a spacing, with extra positions along service trenches and at the edges of fill.

There is no single British Standard for the lightweight deflectometer. Testing usually follows the equipment manufacturer’s procedure alongside a recognised method such as ASTM E2583. On highway schemes the requirement comes from the specification, with performance testing of pavement foundations covered by Series 800 of the Specification for Highway Works.

Roughly one to one and a half plate diameters, so the top 300 to 450 mm with a 300 mm plate. It is a check on the layer you have placed. In the valley ground around Willen and Caldecotte, or over an infilled pit, a thin layer gives a composite reading of the layer and the soft material beneath.

For showing that a layer is uniform, often yes. For proving a piling platform or a crane hardstanding, usually no, because those designs are checked against a plate bearing result at the design pressure. LWD is useful for checking uniformity across a big slab, but it is not a plate test and most designers will not accept it as one.

It can be estimated, but dynamic stiffness and direct CBR are different measurements and the relationship depends on the material. Any conversion must be appropriate to the material and agreed for the project, and reported as derived. With the laboratory close by, a direct CBR is rarely difficult to arrange instead.

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. The accreditation is held at the Milton Keynes laboratory. Ask us to confirm the accreditation status of LWD testing when you enquire, particularly if your specification requires accredited results.

Every visit is quoted from the site postcode, and with almost no travel in it a local LWD visit is about as economical as ground testing gets. The price depends mainly on the time on site. Send the postcode, the area to be tested and your dates and we will quote.

Yes. Milton Keynes is Hixtra’s head office and laboratory, and 01908 505833 rings there. Every team we send anywhere in England and Wales starts the day here, so for local sites the journey is a short one.