BarChip Fibre Reinforced Shotcrete – Primary Tunnel Lining

Client: Sound Transit
Contractor: Guy F. Atkinson Construction
Design JV: Mott MacDonald, Hatch, Jacobs Engineering, HNTB

Completed in 2020, The Downtown Bellevue Tunnel (DBT), part of Sound Transit’s $3.7 billion East Link light rail extension, was delivered on time and under budget, despite challenging ground conditions and tunnelling within just three feet of existing downtown structures.

One innovation supporting the project’s success was the use of BarChip macro synthetic fibre reinforced shotcrete in the tunnel’s initial lining. The DBT consisted of:

• 1,983 ft (604 m) of SEM (Sequential Excavation Method) tunnel
• Two cut-and-cover portals
• A mid-tunnel access shaft and adit
• Excavation directly adjacent to commercial buildings, in some cases within 3 ft of underground structures

While the original specification called for steel fibre reinforced shotcrete, the project team identified an opportunity during construction to optimise testing efficiency and cost control. Rather than treating this as a simple material substitution, the Contractor, Construction Management Consultant, and Engineer collaboratively developed a refined specification and performance based testing regime. This construction phase optimisation:

• Clarified testing requirements
• Reduced ambiguity in compliance procedures
• Mitigated potential testing cost exposure
• Maintained structural performance and safety standards
• Enabled the successful adoption of macro-synthetic fibre in the initial lining

This was not a reactive change, it was a proactive improvement. The DBT demonstrates how collaborative teams can refine specifications during delivery to improve certainty, efficiency and overall project outcomes.