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Project Name: River Road Slope Stabilization

Project Location: Lewiston, ME

feature image showing roadside slope

River Road in Lewiston, Maine, is a beautiful route that meanders through lush landscapes. However, this charming road faced a significant challenge—a steep 1:1 slope—that posed stability and erosion concerns. Moreover, the road carried a heavy volume of traffic, including a constant flow of trucks. The combination of the slope’s steepness and the heavy traffic load created a high-risk scenario, necessitating an effective soil stabilization solution to ensure the long-term integrity and safety of the road.

Recognizing the urgency to enhance the infrastructure and ensure the long-term safety of commuters, the River Road Reconstruction project was initiated. The project included shoulder widening, pavement reconstruction, milling, shimming, and overlay. Additionally, efforts were made to reconstruct a gabion basket retaining wall, construct a stabilized vegetated slope, install an underdrain drainage system, and replace the guardrail.

The Challenge: Stabilizing a Steep Roadside Slope

The River Road Reconstruction project encountered a significant challenge in constructing a vegetated slope with a 45-degree angle. This slope presented a heightened risk of erosion, particularly during the spring season when frequent rainfall and snow melt would swell the brook at the toe of the slope. This would put the slope at a heighted risk of washing out.

The erosive forces posed a threat to the slope’s stability and the integrity of River Road itself. To mitigate these challenges, measures were required to reinforce the slope and establish an effective erosion control system, ensuring the long-term durability and safety of the road.

The Solution: The GEOWEB® Vegetated Slope Protection System

To accomplish this, the GEOWEB Slope Protection System with a vegetated infill was chosen as a soil stabilization and erosion control solution. The construction process involved the strategic use of geogrid lifts. The slope was built in lifts with geogrid layers placed periodically, creating a slope face with a steep 1:1 ratio. This method significantly enhances the overall stability of the slope.

Installation of the GEOWEB Geocell System

river road slope during and after installation of the geoweb geocellsTo keep the topsoil in place on the steep slope, the GEOWEB system was used in combination with a tendon system. The GEOWEB® system is a 3D cellular network specifically designed to stabilize topsoil, promoting sustainable vegetation growth even on slopes with an incline that can reach or even exceed 45 degrees. The system effectively mitigates the risk of severe erosion that can be caused by surface runoff or sheet flow, providing a level of slope-surface stability that 2D planar systems cannot match.

At the slope’s toe, the GEOWEB system was filled with rocks, creating a strong and stable foundation. Larger rocks were placed on top for additional support.

Moving up from the base of the slope, the cells within the GEOWEB system were filled with topsoil, creating a supportive and fertile environment for the growth of vegetation. This topsoil layer was then covered with a turf reinforcement mat (TRM), further reinforcing the structure and promoting the growth of a green cover on the slope.

Overall, the GEOWEB Slope Stabilization System played a vital role in this project, providing stability, soil confinement, and vegetation support for the constructed slope.


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