A STUDY ON THE METHOD OF SUBSURFACE CAVITY SURVEY BY CONCURRENT USE OF PORTABLE FWD AND GROUND PENETRATION RADAR

摘要

In Japan, more than 4,000 road cave-in accidents have occurred each year. Some of them have led to such serious accidents as to affect human lives. In order to avoid serious accidents, therefore, it is hoped to have a technology of discovering cavities efficiently at an early stage. At present, Ground Penetration Radar (GPR) is used as a cavity searching technology, but is not high in the accuracy of cavity detection. In this study, therefore, the applicability of the search method by concurrent use of GPR and portable FWD as a technique for discovering cavities easily and efficiently was verified mainly around the drainage piping in a liquefied community road, a criterion formula by which the presence of a cavity can be determined was proposed and its efficacy was investigated. This investigation was conducted in a low volume road, and in a trial pavement section in which a subsurface cavity had been reproduced. As a result, the use of this search method made it possible to detect ordinary cavities existing at 800 mm below the road surface and made it clear that even such subsurface cavities as cannot be noticed by the GPR survey only can be efficiently detected.