Overview
Holt Services Inc. is proud and excited to support the West Seattle Ballard Link Extension (WSBLE). A major infrastructure project that will expand public transit across Seattle. In partnership with Shannon& Wilson, we’re helping drive forward the critical design phase of this transformative effort.
Spanning 7.7 miles and adding nine new stations between West Seattle and Ballard neighborhood, much of the extension will run underground via a large-diameter tunnel. While still in the design phase construction is currently scheduled to begin in 2028.
Geotechnical and Environmental Drilling Expertise
From the outset, Holt Services has provided environmental and geotechnical drilling services to the WSBLE project. Using a combination of Mud Rotary and Sonic drilling techniques, we’ve already completed over 6,000 feet of vertical exploration with more on the way.
The data we’ve collected is being analyzed by Shannon & Wilson to inform the design of this $7 billion project.
Solving Underground Challenges with Precision
One of the more complex design challenges involves identifying segments of Seattle’s original underground tunnel system. Constructed after the Great Fire of 1889 and later abandoned, these tunnels were backfilled with a variety of materials including timber and concrete creating problematic voids for modern tunnel boring machines.
As experienced during the Alaskan Way Viaduct project, soft or variable materials can damage equipment like the massive ‘Big Bertha’ boring machine, leading to costly delays.
Thanks to experienced drilling crews operating the TSI 150cc Sonic rig, Holt Services can drill through both compacted and unconsolidated soils. Alongside SPT (Standard Penetration Test) sampling we’re able to confidently detect these buried structures helping to prevent expensive surprises during construction.
Urban Drilling with Safety in Focus
Drilling in Seattle’s busy urban environment presents additional challenges: uneven terrain, high-traffic corridors and tight working zones. Our crews and project managers are known for their attention to detail, and maintain the highest standards for health and safety.
Our use of the VacMaster 4000 air knifing tool, available at all four of our locations, allows us to safely expose underground utilities protecting vital infrastructure during our drilling operations.
Inspiring the Next Generation: UW Student Field Trip
One of the highlights of Holt Services’ involvement in the WSBLE project was hosting a field trip for University of Washington students. On a beautiful Seattle day, we welcomed the future of our industry to see geotechnical drilling in action
A big thank you to our partners at Shannon & Wilson, especially:
- Joseph Clare, Project Lead for the WSBLE project
- Brian Stabile, Senior Geologist and Geotechnical Lead
- Brooke Roling, Field Staff, whose insights and mentorship energized the students
And of course, a shout out to the Holt Services team:
- Travis Stephens – Project Manager
- Gavin Hardin (Driller)
- Jeffrey Hall and Juliano Falaniko (Driller Assistants)
Their professionalism and hands on explanations made the day incredibly impactful. The UW students were curious, engaged and full of great questions, it’s clear our industry will be in excellent hands in the future!
Looking Ahead
As the WSBLE project moves toward construction, Holt Services Inc. is honored to continue supporting it with precision drilling, safety focused practices, and community engagement.
Whether tackling subsurface complexities or inspiring the next generation, we’re proud to contribute to projects that move our region forward.