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Phase 1b: I-90 Pass East of Hyak

The view toward Hyak from the west end of the Phase 1b project, the photograph shows the excavation at about half-way to final grade.

ARC was hired by the project rock slope design engineer; Wyllie & Norrish Rock Engineers Inc. (www.wnrockeng.com) as part of their consulting contract for the WSDOT project to widen and straighten a section of the I-90 Highway.  In addition to helping our client adjust their design during construction we documented strength and weathering details to group the rock quality for future engineering evaluation and design.  We provided our recommendations for installing spot rock dowels and rock bolts.  As part of our on-going tasks, ARC continues to create an as-built set of drawings for the slope reinforcement and recommend areas for additional rock cut face support enhancement and drainage.

Our 24-hour on-call consulting services became useful when WSDOT required immediate evaluation of unstable slopes where boulders, on another section of the I -90 pass, fell to block the west-bound Sunday late evening traffic heading back in to Seattle.  You can read more about the history of this project from the paper published on the following Federal Highway Administration link:


Rock slope experts from Pacific Blasting drilling holes for the next blast shot to remove large rockmass blocks above I-90 (Phase 1b).

Phase 1c: I-90 Pass East of Hyak

We continued our engineering services for the rock dowel and bolting on Phase 1c of the project.  Portions of this rock excavation and anchor installation are through the rock mass area sometimes referred to as "Slide Curve" the location of a fatal rock slope failure in the mid-1950's.

Rock mass left in place with rock anchors being drilled and grouted to depths over 40 feet in fractured formation

Collecting data for 3-D stability analysis of the anchored rock blocks.

Drilling (background) for installation of 60 feet long rock dowels about 80 feet above I-90 at Slide Curve.

Surveying on the first bench about 100 feet above I-90 at Slide Curve.