Position estimates for existing trenchless installations

The position and alignment of existing cables and ducts, previously installed by trenchless technologies, has not always been recorded with sufficient accuracy for new works to be safely conducted close to existing installations. Inaccurate or missing registration in the past, manual data entry, previous activities in the same areas, can all lead to deviations between recorded and actual location. Location detection is often hampered by the depth of installations, especially in the case of HDD. The Netherlands Society for Trenchless Technologies (NSTT) has conducted a survey of the accuracy of trenchless installation techniques over the past decades, and of external factors influencing the position of existing cables and ducts, to get an estimate of the positional accuracy of older TT installations. This paper gives an overview of estimated accuracies for cables and ducts installed by HDD, micro-tunnelling, impact moling/ramming, auger boring and other TT installation techniques, taking soil conditions and the state of technology at the time of installation into account. The paper also gives an overview of which TT came to the Dutch market in which period.