CW Microwave Location of Voids Beneath Paved Areas

The problem of locating voids beneath paved areas is a perplexing and costly one. Usually voids are investigated by test borings, which is a discontinuous hit-or-miss process. The use of a continuous nondestructive testing method is a very attractive alternative. One such method is based upon the use of continuous wave (CW) microwaves which can penetrate the upper paved material and, depending upon the nature of the underlying material (soil, air or water), will give different return reflections. Such a method is described and results based on large scale laboratory tests are presented. It is concluded that the method could be used to indicate differences between the underlying material (soil, air or water), but fell short of assessing the thickness of the air void when it was present.