LWD testing in Winchester.

Same-day and next-day dates are often available, subject to the schedule. Winchester is a reasonable run from our laboratory in Milton Keynes down the A34 and M3, and an LWD visit needs only a technician and portable equipment. On chalk, ring 01962 461501 before the formation is trimmed, so the test can follow closely behind.

A lightweight deflectometer measures the stiffness of the surface layer by dropping a known weight onto a loading plate and recording how far the surface deflects. 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 chalk, that speed lets a whole formation be checked before the weather gets at it.

Yes, on intact chalk it works well. Sound chalk has a clear elastic response and gives high, repeatable readings. The surface needs to be trimmed flat so the plate seats evenly. What the test cannot do is make degraded chalk look good: once the surface has turned to putty chalk the readings fall sharply, which tells you the formation needs attention before it is covered.

Often, yes. A CBR plunger is 50 mm across, so a flint under it gives a false high or a refusal. A 300 mm LWD plate spans individual flints and reads the mass of the material. Large flints standing proud of the surface can still stop the plate seating flat, so those positions are trimmed, bedded or moved. Check that your specification accepts a stiffness value.

Not reliably when it is wet. Clay-with-Flints behaves as a clay, deforms plastically under the falling weight and gives little elastic recovery to read. A road can run from chalk onto clay cover and back within a few hundred metres, so expect the readings to change with it. On the clay lengths, a CBR at formation and LWD on the capping above is the usual approach.

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. Tell us the target and the report shows each position against it.

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 will not find a solution feature in the chalk beneath clay cover, or tell you how deep the soft alluvium is on the valley floor. Those are questions for the ground investigation.

For checking a formation or a layer is uniform, often yes. For proving a piling platform or a crane pad, usually no, because those designs are checked against a plate bearing result at the design pressure. Plate tests at the critical positions with LWD across the rest is a sensible plan. Agree it with your designer first.

It can be estimated, but dynamic stiffness and direct CBR are different measurements and the relationship depends on the material. Chalk is a material where the relationship is particularly uncertain. Any conversion must be agreed for the project and reported as derived.

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. Ask us to confirm the accreditation status of LWD testing when you enquire, particularly if your specification requires accredited results, and we will tell you before you book.

Every visit is quoted from the site postcode. With no reaction vehicle and only minutes per position, the cost per test is low compared with plate bearing. Repeat visits are what push costs up on chalk, usually because the formation was not ready or had degraded, so book with a firm date. We can often combine Winchester with work in Southampton, Eastleigh or Basingstoke.

No. There is no Hixtra office in Winchester or anywhere in Hampshire. The 01962 number rings through to the laboratory in Milton Keynes and every team travels from there. Coverage means we attend. It does not mean staff or kit are kept locally.