Road pavements are designed for trucks not cars. Trucks create as much damage as 10,000 cars. In accordance with the fourth power rule, one truck 20% overloaded does as much damage as two trucks or 20,000 cars.

A heavy vehicle bends the pavement introducing some permanent distress into the pavement structure, causing it to fatigue in bitumen and cement bound materials and deform plastically in unbound granular materials, including the subgrade.

Structural Testing is the application of a known load, similar to the dynamic effects of a moving truck and the measurement of the strains, thus produced, in the pavement.

Structural Evaluation is the analysis of this data to determine the characteristics of the pavement materials and computation of the likely performance under load. Structural Evaluation is a proactive study of pavement that enables councils and road owners to produce more realistic and accurate works programs, to better manage resources and to project more accurate budgetary requirements. It is the warning of failure for a section of pavement prior to it being detected visually.

The Falling Weight Deflectometer is the world standard dynamic plate bearing test for the non-destructive testing of the structural capacity of flexible pavement. The equipment uses up to nine seismic geophones to measure the deflection of the road pavement under the application of a known load from a predetermined height. Each test is adjusted, where appropriate, for the pavement temperature at time of testing. 

The equipment is used to:

Assess the structural capacity of the road by using traffic volumes and axle
weights (ESA's).

Assess the remaining life of the pavement under certain temperature, precipitation
and traffic information;

Conduct ‘whole of life’ costs, Net Present Valuations (NPV) and economic
cost benefit analysis of alternate pavement design.

Report layer moduli (stiffness), deflection, curvature and sub-grade CBR;

Produce pavement designs and rehabilitation strategies for selected rehabilitation
sites down to an individual construction plan for each 10m interval or each lane
as determined by Council;

Provide Quality Assurance assessment of recent works to ensure that they
meet design life criteria;

Assess the impact of increasing road volumes, traffic types or load capacities on
the life and quality of the pavement.

The Equipment The FWD unit is a 9000 series processor and is fitted with DGPS and required safety equipment. It has 9 Geophones spaced from under the load cell to 1500mm. The Heavy Weight Deflectometer is used for rigid pavements, airports and port authorities. Units are air portable for movement to and from remote airstrips. This equipment has completed various projects including testing of Cocos Island airport off the Western Australian coast and container loading facilities at Port Botany. Load range: FWD - 7-120 kN HWD - 30-240 kN

What do the results tell you?

Structural Testing provides materials characteristics for the determination of
maintenance, rehabilitation or reconstruction requirements.

Structural Evaluation is used to determine the thickness of additional material
required to meet the intended traffic requirements (Structural Deficit).

Structural Evaluation is used to compute the remaining structural life of a pavement
in order to determine the Asset Valuation under AAS27.

Structural Evaluation is used to ensure road contractors build new and existing
roads to required design standards.