TRENCHLESS & MICROTUNNELING | VIEWPOINT
Counter points to watch for in engineering include the
larger diameters have increased risk of face instability and also there larger tunnel volumes means more buoyancy forces have to be calculated out. Among Bessac’s many projects, a recent one was
undertaken was in Paris, France, involving a MTBM on VL8 package 3. The works were to create a 2.5m (8.2ft) i.d. raw sewer
over a length of 980m (1072yd), located upstream of a wastewater treatment plant. Tunneling for the MTBM involved a 500m-radius (547yd) curve. He adds that the radius is well within the capability of the industry for a curve without the need for a jack control system. Geology along the alignment comprised conglomerate, limestones and sand.
VIEWPOINT: BARBCO Trenchless Tunneling using Guided Boring There are various ways that trenchless tunneling is completed today. However, one of the most effective, and accurate is through the use of a guided boring machine (GBM). Guided boring is a highly accurate method for the
installation of pipes, conduits and cables using a surface launched drilling rig. A pilot bore is drilled using a rotating drill string and is then opened up to your required size for the product pipe by using a reamer. The method of guided boring is used in a range of
trenchless techniques, such as horizontal directional drilling (HDD), auger boring, and pipe ramming. During drilling when line and grade is crucial, the bit is laser guided allowing for a high degree of accuracy, often within 1 inch (or less) tolerances.
Barbco’s Pathfinder technology is a state of the
art Guided Boring System, to combine the proven technology of a pilot tube steering system with the dependability of a conventional auger boring machine. The company says this delivers accurate casing installations up to 60” diameter. The Pathfinder Guided Boring System was introduced in 2005 and has been used in hundreds of instances, it adds
VIEWPOINT: BARHALE, FROM UK Rod Young, Chair of British Tunnelling Society (BTS) and Senior Contracts Manager & Construction Manager with Barhale In a recent profile interview for his time so far as BTS Chair (since mid-2022), Young made the following points of his work in microtunneling: “Most of the people who have been Chair of the BTS
over the years have been involved in larger diameter projects – the likes of Crossrail, London Thames Tideway, HS2 – the prestige projects of the world just now and all the ones that have gone before. “And the Chairs have tended to alternate between
designers and people on the contracting side. I am neither: I am a practical person, and my background is very much in the smaller diameters. I’ve not done anything more than about 4m or 4.5m (13.1ft or 14.8ft). “So I’m slightly different from my BTS predecessors.
But though tunneling at 2m-diameter (6.5ft) and below may not be so glamorous it is still important. Cables, water, sewerage, communications – wherever something like that has to go under a road or railway you need it. You could call it bread and butter tunneling.”
Above: Recent Bessac sewer tunnel project in Paris, France PHOTO CREDIT: BESSAC Spring 2023 | 21
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