Topaz Bridge Expansion & Replacement

Idaho’s heavily used trucking route and bridge (circa 1940) expands from 2 to 4 lanes to increase safety and capacity using InsulFoam Geofoam.

Idaho Transportation Department’s first EPS Geofoam project was designed by Terracon Engineers and JUB Engineers of Boise.  EPS was specified as a soil replacing embankment fill material due to poor foundation soils and 2 steel fish culverts that could not bear the weight of traditional soil fill.  A new three-span, bridge replaced the existing bridge (from the 1940’s) crossing rail road tracks and expanding the highway to 4 instead of 2 lanes.  

23,000 cubic yards of large block EPS was installed by Scarsella Brother Inc. and supplied by Insulfoam.

The Problem

The expansion of the US-30 and bridge replacement required a new fill embankment to support the new roadway and bridge approach on a very steep side slope.

The new (600 ft long) expanded bridge clears The Pontneuf River as well as the Union Pacific Railroad tracks, and required a new higher grade of both the bridge structure and the existing roadway to support the new wide and long center spans.

The Solution: EPS Geofoam Fill

To reach the new bridge’s approach embankment height of 45 feet, engineers chose a combined fill solution.  The lowest 15 feet was a small earthen embankment, while InsulFoam GF constituted the upper 30 feet.  4 1/2 feet of granular fill retained in wire gab ions and an asphalt pavement section were installed directly on top of the EPS blocks to complete the full height of the new embankment.

The soft sediments underlying the site required the lower earthen embankment to settle (80 days), but the InsulFoam GF block fill required no additional surcharge time or secondary compaction by the contractor.  Traffic moved on the existing roadway throughout the installation of the upper embankment, which was a key factor for the expansion to finish when weather conditions permitted.

The ultra lightweight nature of EPS allowed the total design weight of the tall embankment to be week under the bearing capacity of the poor foundation soils which aided ITD in successfully completing their first EPS Geofoam project.

Geofoam Lightweight Geo-synthetic Fill:

• Soft Soil Remediation
• Lateral Load Reduction
• Slope Stabilization
• Buried Utility Protection
• Structural Void Fill
• Predictable Elastic Modulus
• Exceptional Strength & Stability
• Exceeds 75 year Design Life
• Weather, Insect & Mold Resistant
• 100% Recyclable