Light Weight Deflectometer Capability for Harrison Group
The Light Weight Deflectometer (LWD) apparatus is used to provide in-situ measurement of the foundation surface modulus (E) of the subgrade for use in pavement design. It is also useful in compaction control for bound and unbound base layers and sub-bases.
The foundation surface modulus is a measurement of the stiffness of the layer upon which the test is undertaken in terms of transient deflection caused by the application of a dynamic stress through a circular plate. The test method is set out in BS 1924-2:2018, 9.2 “Hydraulically bound and stabilised materials for civil engineering purposes, Part 2, Sample preparation and testing of materials during and after treatment” but is also referenced in ASTM Standard E2583-07: 2011 “Standard test method for measuring deflections with a light weight deflectometer (LWD).”
The standard test equipment comprises a 300mm diameter plate which is dynamically loaded through a buffer system to produce a load pulse of 15 ms to 30 ms duration using a 10kg weight falling from a variable height (generally less than 1m) to impart a target stress in the order of 100kN/m2 (100+/-5 kN/m2). The actual stress imparted is measured by a load cell within the equipment and the resulting deflection is measured by a geophone in the centre of the plate to a precision of +/-2µm.