Which method of measuring road stiffness is better, Benkelman Beam Test or Falling Weight Deflectometer Test?

Pavement surface deflection measurement is the principal means of evaluating a flexible pavement structure because the magnitude and shape of pavement deflection is a function of traffic, pavement structure, temperature and moisture affecting the pavement structure. Deflection measurements can be used in back calculation method to determine the stiffness of pavement structural layers.

The Benkelman Beam measures the static deflections and it is operated on the basis of lever arm principle. Measurement is made by placing the tip of the beam between the dual tires and measuring the pavement surface rebound as the truck is moved away. The test is of low cost but it is time consuming and labour intensive in carrying out the test.

In Falling Weight Deflectometer Test, the falling weight deflectometer is mounted in a vehicle. The sensors are lowered to the pavement surface and the weight is dropped. The test measures the impact load response of flexible pavement. It has the potential advantages that it is quick to perform and the impact load can be readily changed. Moreover, the impact action of falling weight appears to be more accurately representing the transient loading of traffic.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.