Benkelman Beam

Benkelman beam is used to measure road surface deflection due to the axle pressure of a vehicle with defined load. 

The Benkelman beam consists of a balance arm (in two parts) that pivots about a ball-bearing mounted axis and a frame supported on the ground by three feet on height-adjustable ball-joints.  There are correlation charts available for deflection results to CBR.

http://www.cebtp.fr/vente/benkelman/benkelman_us.html

There are many different approaches to solving the same problems you may wish to look up some of the links below.
 

http://hotmix.ce.washington.edu/wsdot_web/Modules/09_pavement_evaluation/09-1_body.htm
This link is very good grounding and well defined, cover a whole range of subject matter.