Slope stabilization and moisture control on Old Pacific Highway

Overview

The Old Pacific Highway is the original freeway section which runs parallel to the current Interstate 5. Nestled on the hillside, a global stability issue created a slide of the natural slope and a large crack in the pavement section.

Challenge

This project was treated like a deep patch repair and initial repair strategies conceptually included the removal and disposal of the existing asphalt roadway and aggregate subbase, over-excavation of native subsurface soils to a depth anticipated between 2 and 6 ft, the installation of four layers of geogrid in combination with Crushed Surfacing Base Course (CSBC), and Hot Mix Asphalt (HMA) surfacing. However, during geotechnical exploration, an area of high saturation was noted at the bottom of the slip zone, approximately 6 ft down from the existing road surface. The project team was worried that if they repaired this section without addressing the moisture issue, it would not be long until the same section of roadway required additional repair.

Solution

The MIRAFI^® H₂Ri system was selected because it provides a long-term defense against saturated soils under the steepened slope. The main goal was to prevent accumulation of moisture below the slope repair, where there is a known slip plane which has been problematic. The project team acknowledged that the saturated zone would be a continuing problem. The MIRAGRID^® Miramesh facing met aesthetic requirements and long-term performance. The revised solution did not deviate much from the anticipated repair plan and allowed the project team to move forward without over excavation and increased reinforcement lengths.