Abstract Manager

Stantec provided preliminary and detail design for a heavy haul road overpass that traverses a main access road. The overpass consists of three heavy haul road lanes, each approximately 20 m wide. The overpass haul road double lanes will be used for material transport while the single haul road lane will be used for overburden transport. The total overpass width measured at the roof slab is approximately 71 m.

During preliminary engineering, Stantec reviewed several scenarios. A rectangular concrete structure with two cells was selected as the most cost-effective option and site constraints.

Oversize concrete barriers are located along each side of the overpass, above the main access road. The main access road consists of two single traffic lanes traveling under the proposed overpass. Traffic on the access road is comprised of light vehicle traffic. As a safety requirement for the project, the oversize barriers are designed to stop or redirect the heavy haul trucks in the event of a collision.

Standard highway codes requirements don’t relate directly to the design of barriers for bridges transporting extremely heavy trucks (Komatsu 980E-4, GVW= 6134 kN). The current code design provisions allow for the use of new barrier systems provided that an acceptable performance is demonstrated through full-scale crash tests. Conducting a full-scale crash test of a fully loaded heavy truck impacting a bridge barrier is impractical so modeling techniques were utilized. This required the development of an appropriate approach geometry as well as barrier loading parameters.  The modeling included an advanced method to drive the applied loads from the barriers to the structure.

In addition, any debris generated on the overpass, including haul truck material and overburden , has the potential to travel downslope or free fall from the top of the concrete barrier and impact light duty vehicles traveling the main access road. As part of the detail design, Stantec completed a quantitative rockfall simulation to mimic the trajectory for rocks or hardened soil clumps falling from the haul trucks and provided recommendations for mitigative measures (an engineered rockfall fence to capture rocks and debris).

The presentation will walk the attendee through the rationale for selecting the final structure layout and design. In addition, a summary of the barrier design procedure as well as the catchment fence parameters and concepts will be provided.