LWD testing in London.

Same-day and next-day dates are often available, subject to the schedule. We do not guarantee an attendance time, because the M1, the M25 and the roads inside the North Circular decide it. An LWD visit is easier to plan than plate bearing, as there is no reaction vehicle to route through the city. Ring 020 7993 5733 with the postcode.

A lightweight deflectometer measures the stiffness of the surface layer. A weight is dropped down a guide rod onto a loading plate and a sensor records 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. The whole kit fits in a small van and is carried to the position by hand.

Yes. That is where the method is most useful in London. The equipment is carried by hand down a stair or scaffold, so basement formations, granular build-up over podium and transfer slabs, internal courtyards and landscaped decks can all be tested. Tell us about access routes, headroom and any permit requirements when you book.

Not reliably when it is wet. London Clay at formation deforms plastically under the falling weight and gives little elastic recovery for the equipment to read, so results scatter. Specifications on the clay normally assume the wet case and call for a capping layer, and that layer is what the LWD should be testing. For the clay itself, use a CBR.

No. A crane hardstanding or piling mat is designed to a bearing pressure, and the check is a plate bearing test at the positions the outriggers or tracks will load. Most designers will not accept an LWD as a substitute. What it can do is show that the rest of the mat is as good as the positions that were plate tested.

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. For slabs, podium build-ups and hard landscaping the engineer usually sets a project value. 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 checks the layer you have placed. It will not tell you about a backfilled basement two metres down or peat under a marsh platform, which is why a DCP or the ground investigation is needed alongside it on that kind of ground.

Yes, where the backfill is granular. It is a quick way to check that each layer of backfill to services, drainage runs and basement walls has been compacted consistently, in places where no larger equipment will fit. The trench needs to be wide enough to seat the 300 mm plate flat, and your specification should say what value is acceptable.

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. If a borough or adopting authority wants a CBR, a CBR test is the cleaner answer.

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. In London the saving is in time and access: no reaction vehicle to route, no waiting for a clear path to each position, and only minutes per test. The price depends mainly on the time on site. Send the postcode, the area to be tested, any restricted hours and your dates.

No. There is no Hixtra office in London. The 020 number rings through to the laboratory in Milton Keynes and every team travels from there. Coverage means we attend, not that we keep staff or kit in the borough.