Ground cavities next to sewers mapped using in-pipe ground penetrating radar (GPR)

摘要

Maintenance of sewers in towns and cities all over the world requires large financial resources. One way tornoptimize the usually limi ted funds avail able, could be to apply better survey tools. The better the tools appliedrnin the planning process, the better decisions can be made on how to spend money on maintenance. Cavitiesrnformed in close contact with broken or otherwise malf unctioning sewers represent a well known and seriousrnproblem, which is difficult to approach with existing survey techniques. Causes of cavity formation arerndiscussed, and a technique for locating cavi ties using ground penetrating radar (GPR) is presented. Largerrncavities can sometimes be mapped from the surface using GPR, but when conductive soil s are encounteredrnthis technique is not feasibl e. Also, small cav ities at some depth cannot be identifi ed and mapped from thernsurface. A technique to locate cavities from the inside of a sewer was therefore developed and tested onrnartifici al cavities build into working sewer systems. As an alternative to the wait-and-see approach where it mayrnbe necessary to repair after the collapse of big cavities, it is possible - as part of a maintenance plan - to locaternsmaller cavities and apply proper repairs at an early stage and at a convenient time.