Direct Pipe Developments in New Zealand

Abstract

Since its introduction to New Zealand in 2017 McConnell Dowell has keep its equipment busy having now completed six Direct Pipe drives, installing over 14Km of pipeline. Including three wet recoveries and two world records for drive lengths (1.9Km and 2.1Km). Lessons from previous drives have driven change and since no two projects have the same ground conditions, restraints or client requirements the methodology today has been adapted and now used differently to the first Direct Pipe drive in 2018 at Arm Bay. Pushing the boundaries of what can be done has led to the development of a “Hybrid” methodology to install GRP pipe, and “short pipe” launches for constrained sites. This paper covers the projects and influences that have led to these developments and hopes to widen the industry’s understanding of Direct Pipe. Clients often struggle to see where Direct Pipe fits with other methodologies. It has a wider trenchless application where it can reduce risks for clients and contractors by utilizing its unique features that can lower or reduce construction risk and uncertainty. Using a decade of experience in New Zealand and Asia, combining operational lessons, internal Engineering and leveraging strategic relationships we have developed pragmatic, collective approaches to technical and client issues. This has implications for the wider trenchless industry as it is an example of evolving methodologies and how our industry can innovate. 1. SYSTEM INTRODUCTION Direct Pipe is essentially a micro-tunnelling operation with some HDD features. It’s a single pass methodology with slurry micro-tunnelling’s abilities in a wide range of ground conditions combined with retractability and a capability of installing accurately over long distances (so far 2.02Km) in a single drive. It often gets compared to HDD and 1 No-Dig Down Under 2025 Direct Pipe developments in New Zealand Paul Cooper micro-tunnelling despite being a different operation that should not directly compete as it is designed to deal with different conditions that are typically not suited or high risk for other methods. It was developed by Herrenknecht by combining a steel casing thruster used for long HDD pull in assistance (pipe side) and their standard slurry microtunnelling TBM. If comparing with HDD, the key methodology differences are: • Use of thrusters with clamps to thrust ridged pipes. • Single pass that can retract. • Fully supported bore using the carrier pipe with a lubricated annulus - little reliance on complex bentonite slurry mixes to hold the bore open. • Relatively little non-pressurized over-cut of 60 to 70mm. • Full hydraulic support of TBM face. Figure 1: Direct Pipe Section showing key features - telescopic section, and conical interface ring (from Herrenknecht) With reference to figure 1, key features that make it different to a normal AVN TBM are: • While a standard option, a power pack in the TBM head is required due to the distances achieved. • Unusual for a smaller MTBM, inclusion of a telescopic section, as there is no opportunity for inter-jacks. • Bentonite injection unit ahead of a conical interface ring reducing the OD from 1350mm to 1220mm. • Direct Pipe launch frame and articulated launch eye. • Using a thruster and clamp to provide forward and back thrust. The thruster and clamp are located where you would normally see a jacking frame and yoke with a micro-tunnel operation. The thruster has a 5m stroke and is fixed to the clamping unit that hydraulically grips the steel carrier pipe. The pipe is either welded or bolted to the rear of the TBM with the bolted solution used for wet recovery. These are carrier pipes that are preloaded with services, pumps and rails and then connected to the installed casing with a connecting weld undertaken on the installation critical path. 2 No-Dig Down Under 2025 Direct Pipe developments in New Zealand Paul Cooper

Techniques