LWD Deflection Testing Contaminated Site

Contaminated sites present opportunities but can also pose significant risks. Asbestos and Per- and polyfluoroalkyl substances (PFAS) are often encountered by our clients.  

They can be found on open development sites with a history of industrial usage or on sites affected by overland water flow. As a solution to contamination, a project can also involve burial within a secure containment cell of contaminated soils, particularly solid, non-aqueous phase contaminants such as asbestos containing materials (ACM). 

Nuclear Density Gauge NDG Meter

Our traditional methods of measuring the compaction of soils using the Nuclear Density Gauge is a problem because it requires disturbing the material surface and penetration into the soil, when hammering the spike into the ground. 

A sample of the material must then be taken off site for compaction testing. On contaminated sites, this is often not acceptable where the movement off site of such materials is to be minimised. 

A number of our clients have been turning to the Light Weight Deflectometer (LWD) to help with this specialist application. The device is non-destructive (does not disturb the underlying soils) and does not require off-site testing, it is therefore ideally suited to this specialist application. 

Light Weight Deflectometer Contaminated Site Asbestos Compaction Myilly Point ACM Containment Cell

Here is an example, courtesy of WANT Geotechnics, of the LWD in use in a containment cell being filled with soil contaminated with ACM. The cell was 5m deep and filled in a series of layers with each layer tested at several locations with the LWD to confirm the compaction methodology met the specified degree of compaction for the aboveground end-use of the cell (car parking). 

The Light Weight Deflectometer is used to determine the stiffness of unbound materials (subgrade/subsoils and base layers, granular layers & backfilling materials) or partially bound material (e.g. stabilised) during construction or pavement rehabilitation. 

Modulus is the most accurate and independent means for judging deformation (stiffness) and, thus, a material’s level of compaction. By measuring the modulus value, the LWD provides the direct link between the design specification (design modulus value) and the actual site condition (in-situ modulus value). 

The Light Weight Deflectometer (LWD) is repeatable, fast (test is done in 3 minutes) and gives you immediate GPS located results. 

Consider it next time you have a contaminated site that you need to measure compaction on.