Surgical precision: Micro tunnelling in Surburbia

North Shore City Council (NSCC) has carried out numerous major wastewater upgrade projects under their Project CARE scheme since its implementation in 2000. NSCC approach their projects in terms of not only considering their whole life costs, but evaluating other parameters including the level of public disruption, environment sustainability and the ease of consenting. A significant number of the projects have been built using trenchless technology including by micro tunnelling and directional drilling methods.

Micro tunnelling has been successfully used by NSCC to install wastewater gravity sewer pipelines at various gradients, including some that are extremely flat. Its use presents some specific and unique risks from design to construction that need to be clearly evaluated and closely managed to ensure the project is to achieve or surpass its objectives.

The main feature of micro tunnelling is the ability to install straight lengths of pipeline underground to a very consistent and accurate grade. This is the ideal situation for gravity sewer pipelines.

This paper will describe the features of NSCC’s projects that have resulted in the use of micro tunnelling as the adopted methodology, and look at key attributes, risks and challenges when considering this methodology. Specific projects on the Project CARE scheme will be referenced. The paper will conclude with successes and lessons learned on micro tunnelling projects which have been incorporated into further stages of the Project CARE scheme as a whole.