Combining Systems for Optimal Performance

The Hixson Athletic Association fields in Chattanooga, TN have been home to community sports and recreation for more than 30 years. A slope failure near the southwest corner of the track needed to be remediated and stabilized. The slope is 12 feet tall with a gradient of approximately 1.53 Horizontal: 1 Vertical (1.53H:1V), and the failure depth was approximately two feet. The slope was experiencing saturation caused by flooding from storm sewer pipes located above the slope, coupled with flooding and ponding from a surface water drainage channel at the toe of the slope. The slope needed to be stabilized to prevent further washout, which was impairing the track. The track is widely used by young children, and the City wanted an option that would reduce risk with respect to pedestrian park use.

The City considered using a modular block wall or rock riprap to stabilize the slope, but both options are costly and do not provide a natural look. The City chose to use a combination of SCOURLOK® and ARMORMAX® by Propex GeoSolutions to address the slope failure and erosion. Previously the City had used this same combination to repair a slope at a local elementary school and its performance has exceeded expectations.

SCOURLOK was used to protect the toe of the slope. Its design features rigid cells armored with superior erosion control protection from PYRAMAT® 75 High-Performance Turf Reinforcement Mat (HPTRM) along with the separation capabilities of GEOTEX® Nonwoven geotextile. ARMORMAX was installed on the slope above the SOURLOK system to further stabilize the slope and prevent future erosion. ARMORMAX combines High-Performance Turf Reinforcement Mat (HPTRM) with Engineered Earth Anchors™ to provide surficial slope stability. It also resists both hydraulic and non-hydraulic stresses, meaning that the site can be maintained by mowing and other landscaping equipment without fear of damaging the HPTRM.

Three cross-sections in the area of the failure were cut from the survey data that was provided. The cross-sections were then used to create a typical section for analysis. Propex’s geotechnical analysis and design for the slope considered the sliding, overturning, and bearing capacity of the SCOURLOK units and the surficial stability of the slope with ARMORMAX. The wall cross-section consisted of one row of SCOURLOK units with a half-foot base embedment with ARMORMAX on the slope above the SCOURLOK units. The slope cross-section behind the SCOURLOK units consisted of an eight-foot-tall slope with a maximum gradient of 2H:1V.

Analysis on three scenarios was completed using Propex’s GeoDesign web-based geotechnical modeling application: Sliding, Overturning, and Bearing Capacity. The lateral earth pressure was evaluated based on the project information and used to determine the Factor of Safety provided by SCOURLOK in these three scenarios. SCOURLOK exceeded the required Factor of Safety for all three.

Additional analysis showed that using ARMORMAX with B2 anchors improved the Factory of Safety over the unreinforced condition and significantly reduced the probability of failure for the given soil parameters. ARMORMAX also provided surficial erosion control and vegetation reinforcement. Both systems promote rapid root development and encourage the growth of vegetation. Together, this combination will provide up to 75 years of vegetated slope stabilization and erosion protection.