Last Word: Pilot Tube Method Gets New Manual of Practice

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Pilot Tube and other Boring MethodsA group of dedicated engineers, owners, suppliers, manufacturers and contractors have been working over the past three years to write a Manual of Practice (MOP) on Pilot Tube and Other Guide Boring Methods. The MOP has been assigned the number 133 and is scheduled for release in July.

This group has been meeting via biweekly conference calls and several times a year with face-to-face full-day sessions to write, rewrite and address ASCE’s Blue Ribbon review comments of the MOP. The group has been working closely with contractors to assure that their interests and collective experience and wisdom are included in the document.

MOP 133 takes into account the many changes and advances in pilot tube and other guided boring methods that have occurred over the years. The document covers the design and installation of utility pipelines under roads, railroads, constructed and natural structures, and other surface obstacles.

The pilot tube method is a multi-stage technique of accurately installing a pipe to line and grade by use of a guided pilot tube followed by upsizing to install the pipe. The associated methods can be effective tools for the accurate installation of pipelines, including those installed with auger boring, pipe ramming and HDD. The document also discusses the use of pilot tubes as a probe to look for buried objects in the path of microtunnels and large TBM driven tunnels.

MOP 133 provides detailed descriptions of the pilot tube and other guided boring methods through chapters on the equipment and installation steps, project planning, site and geotechnical assessment, shaft design, pipe characteristics and design, contract documents, and construction aspects.

Chapter 2 provides a detailed discussion of the equipment and process including inserting the pilot tube, types of slanted steering heads and jacking frames. The discussion continues with the enlarging of the pilot tube path with thrust casings, reamers and cutter heads, and powered reamer/powered cutter heads. The chapter also discusses how the pilot tube is used to guide other trenchless methods. The last section discusses the latest variations and refinements to the pilot tube method, which includes working in non-displaceable soils and rock, front steer systems, vacuum excavators, and other guidance systems using internal light sources.

The sections on Planning (Chapter 3) are designed to assist the owners and engineers in laying out and preparing preliminary designs for an efficient project, including shaft and workspace requirements, routing considerations (vertical and horizontal), geotechnical considerations, service connections and impacts to adjacent structures. The chapter outlines what is needed to successfully plan and design a project.

Chapter 4 discusses detailed site investigations needed with a focus on the geotechnical assessment, approaches and methods, including depth and spacing of geotechnical borings as well as identifying geophysical and other investigation methods that can be used for better defining the subsurface conditions that may be encountered. Included in the chapter is a table outlining the applicability of the pilot tube method for different ground conditions.

Sections on design and construction of shafts are presented in Chapter 5 and include types of shafts, including the design of entry and exit seals for shafts and stabilization of surrounding ground when launching or receiving the trenchless equipment.

The sections on pipe materials (Chapter 6) were prepared by representatives of pipe manufacturers. The engineers and contractors have provided valuable input as to what is desired in the industry from both an installer’s and an owner’s standpoint. Important characteristics include pipe dimensional tolerances, lubrication ports and pipe joints.

Methods for preparing Construction Contract Documents are addressed in Chapter 7. This section also addresses not only the qualifications of the contractor to construct a pilot tube project in specific conditions, it also recommends qualifications for the engineer who will evaluate, engineer, design, prepare contract documents and potentially provide oversight for the owner. In addition, methods for managing disputes have been included.

Finally, sections on construction of the pipeline have been incorporated (Chapter 8). These include recommended best practices for pre- and post- construction activities, contractor submittal and review requirements, and the recommended inspection practices by the owner or their designated representatives. Also included are construction topics, such as jobsite layout, surveying and lubrication.

The document will be unveiled at the ASCE/UESI Pipelines Conference in Phoenix, Arizona, at a four-hour workshop taught by the principal authors on Sunday, Aug. 6 starting at 1 pm. Attendees will receive a hard copy of the MOP. To register for the workshop, check the ASCE Pipelines 2017 Conference website.

The principal authors of the MOP include Jeff Boschert, Glenn Boyce, Dennis Doherty, Andrew Finney, Richard Palmer, Troy Stokes, and Nick Strater. The task committee chair is Mohammad Najafi.

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