ABSTRACT
One of areas of risk associated with the use of trenchless service installation methods is how close they can be used to existing service lines without causing damage. This paper describes recent research that has been conducted, based on numerical simulations and field trials using both impact moles and horizontal directional drilling units, to assess the influence of these operations on the adjacent ground and existing service lines.
The controlled field trials carried out at part of this research involved placing instrumentation in the ground and monitoring the ground response resulting from various trenchless operations. The results from these trials were then used to verify numerical modelling results. The numerical modelling was conducted in FLAC 2D, modelling both a longitudinal section and a perpendicular section to the line of the new installation. This allowed a number of parameters to be altered and assessed, for example ground type, impact mole diameter and depth of installation. The package also allowed pipelines to be placed within the vicinity of the trenchless operation being simulated. This enabled an assessment to be made of the likely damage to existing services.
The result of this work has been a set of safe proximity charts for impact moles and horizontal directional drilling units related to different types of ground condition. This paper describes some aspects of the field trials and numerical work and gives examples of the safe proximity charts that have been produced.
