Stabilizing Red Hill landfill cap with PROPEX Armormax

Overview

In 2019, the Red Hill Landfill in Northern California faced a significant slope failure due to heavy winter rains. The 100-foot (30 m) slope experienced depths of failure ranging from 1 to 2 ft (30 – 60 cm), primarily attributed to the sloughing of the top vegetative layer. This sloughing was believed to be caused by the movement of a saturated vegetative soil layer over a low-permeability clay cap layer. Recognizing the urgency of the situation, Geo-Logic Associates sought assistance from Solmax engineers in 2020 to provide a solution that would address the slope failure effectively.

Problem

After working closely with the team, the PROPEX^® Armormax system was chosen for the project. This solution combines PROPEX Pyramat^® 75 High-Performance Turf Reinforcement Mat (HPTRM) and Engineered Earth Anchors to address erosion control and surficial slope stability challenges effectively. The familiarity of the landfill owner/operator with PROPEX Armormax from a previous successful installation in 2016 instilled confidence in the chosen solution and its potential for delivering satisfactory results.

The failure of the slope at Red Hill Landfill posed several challenges. The existing landfill cover consisted of a 4 ft (1.2 m) thick structure, including a 1 ft. (0.3 m) vegetative soil layer, a 1 ft (0.3 m) low-permeability clay layer, and a 2 ft (0.6 m) foundation layer of compacted select soils. The slope's instability threatened the integrity of the landfill and environmental and safety concerns. It was crucial to find a solution that would enhance stability, reduce the risk of future failures, and provide erosion control and vegetation reinforcement.

Solution

Solmax engineering department successfully collaborated with Geo-Logic Associates, utilizing geotechnical analysis to devise a comprehensive solution. A stability analysis incorporating PROPEX Armormax with 9 ft. (2.7 m) deep B3 anchors demonstrated a significant improvement in the Factor of Safety (FoS) over the unreinforced condition, reducing the probability of future failures.

The solution also provides resistance to erosion and distributes the load among the anchors, while the engineered anchors are designed to permanently secure the PROPEX Pyramat 75 HPTRM and increase surficial slope stability. Because Solmax offers a great range of anchor options within the PROPEX Armormax system, this allows for customization based on specific project requirements and challenges. By implementing the PROPEX Armormax system, the Red Hill Landfill can effectively stabilize the slope, mitigate risks of further failures, and ensure the long-term integrity and sustainability of the landfill site.