Abandoned Coal Mines Make for Challenging HDD Design and Installation

The Southwest Edmonton Connector (SWEC) project is meant to replace one of ATCO Pipelines existing vintage high-pressure pipelines with 21 km of 508 mm diameter pipeline. The Whitemud Creek Crossing is a horizontally directionally drilled installation beneath a 30 m deep ravine lined with unstable slopes with existing infrastructure. Along this ravine are exposed seams of coal that were extensively mined which created hundreds of meters of room and pillar mine works which extend in all directions centralized at the Whitemud Creek. An extensive geotechnical investigation was planned and executed which included seismic tomography to determine the potential for voids and presence of existing mine works. A ground improvement plan was developed and executed with a total of 105 grout holes. Borepath design, hydrofracture, and pipe stress analysis were supplemented with a parametric study using the finite element method to optimize the pipe wall thickness within the limits of the ground improvement zone. This paper outlines the design and construction methodology utilized to successfully complete the 700 m long crossing of the Whitemud Creek.