Session: 02-04-2 CONSTRUCTION - Best Practices/Techniques

Paper Number: 134161

134161 - Raise Bore Pipeline Lowering System Design: CGL Section 8W Steep Slope 3 

Abstract: 

Coastal Gaslink's (CGL) 48-inch diameter natural gas pipeline, stretching from Dawson Creek to the LNG Canada Facility in Kitimat, BC, Canada, employed various construction methods for challenging terrain, including several steep slope techniques to navigate the Rocky and Coast Mountains. Steep Slope 3 (SS3), located on the pipeline alignment at the mouth of a hanging valley in the Coast Mountains west of Icy Pass, involved terrain limitations due to steep rock slopes and exposure to rockfall and avalanche hazard.

These terrain limitations would prevent access to concurrent work beyond SS3 with a typical open-cut crossing through the slope. Consequently, the solution for the approximately 120-meter high slope crossing necessitated a trenchless approach employing a raise bore and tunnel methodology. This innovative approach condensed the construction schedule and facilitated continuous access via a shoofly road to concurrent work fronts, allowing simultaneous construction progress beyond SS3. 

Building on insights gained from the raise bore construction experience of the El Encino – Topolobampo pipeline, the SS3 project necessitated a specialized lowering system for inserting the carrier pipe into the 60° raised bore. This system design had a 4:1 mechanical advantage capable of restraining larger loads associated with the 48-inch pipe. The carrier pipe installation design included lowering system components and low-strength grout backfill.

The lowering system comprised two surface-level pulleys, a steel lowering frame housing four additional pulleys, and a lowered head fitted with four sheaves. A static winch controlled the carrier pipe lowering. The lowering system load of approximately 112 ton and 120 m length of carrier pipe required a novel application of existing steel, wire rope, and lifting codes and standards. For consistent backfill quality, the low-strength grout backfill method used tremie lines in multiple stages.

The successful execution of the SS3 raise bore installation reduced geohazard exposure during pipeline construction and yielded significant schedule efficiencies. This proposed paper describes the relevant standards and codes for design of a trenchless raise bore pipe installation. 

 

Presenting Author: Bret Shandro 6 Point Engineering

Presenting Author Biography: Bret enjoys working on solutions to challenging problems in mountain environments. While working on various linear infrastructure and mining projects, I have provided a range of civil, structural, and geotechnical engineering services.

Authors:

Bret Shandro 6 Point Engineering
Greg Johnson 6 Point Engineering
Cam Ross 6 Point Engineering
Alex Jean Ledcor Haisla Limited Partnership
Herman Lee Ledcor Haisla Limited Partnership
Curtis Berube Ledcor Haisla Limited Partnership
Arend Deelen Coastal Gaslink