The utility industry is regularly required to call on an enormous and varied range of specialists; from mapping, to drilling, to wastewater treatment, to asset management, to pipe relining, to pipeline integrity, to land access, to risk management, and the list goes on. To make the process a little easier, Utility magazine is bringing together experts from various fields to answer your questions.
With the HDD industry there certainly appears to be a recognisable trend developing – longer drills. Notice I have omitted to also include larger at this stage, as the practice still relies on creating an unsupported hole for the pipe or pipes to be inserted into.
Creating a large diameter hole leaves us somewhat dependent on the soil integrity and strength, unless a step change is made to the process.
Herrenknecht’s DirectPipe technology has gone some way to address this by installing the pipe or casing directly behind the cutter, however distance achieved is restricted by the skin friction that develops from the narrow gap created between the pipe and formation.
The HDD industry already competently installs steel pipelines up to 48” diameter and, in reality, end users rarely require diameters over this size to be installed. Once the diameter does become larger than 48”, the construction of a concrete tunnel is generally advocated as lower risk and accepted as the norm.
Advancements such as intersect technologies (which allow crossings to be drilled from both sides meeting in the middle), larger capacity drilling rigs and the availability of pipe thrusters to aid pipe insertion, have all allowed for much longer lengths to be regularly and reliably achieved. Of particular note is the use of intersect drills, which has effectively allowed drill lengths to be doubled overnight. A plot of a selection of notable large project completed over recent years is above right.
From the graph, it is reasonable to infer that lengths of 4.5km of 12” pipe and 2.5km of 42” pipe are now within industry capability. This capability will allow for greater flexibility in construction options and clients should be incorporating this advancement in technology into their concept designs and studies and not just staying within safe margins.
I believe the HDD industry will drill longer yet, aided by further developments such as industry-specific software for analysing drill pipe pressures, fatigue and stress, telescopic casing to provide hole support whilst reducing torque and drag, mud programs and modelling for better hole cleaning and hole support, and equipment advancements including telescopic rigs for faster tripping times.
So longer, in excess of 4.5km, appears to be the way forward, for now.
About Charles Stockton
UK-born Charles Stockton has been a part of the HDD sector in Australasia since 2003. He is the Managing Director of Stockton Drilling Services, a leading engineering consultancy specialising in HDD and other trenchless pipeline installation methods.