A scheme to stabilize minor slope instabilities is currently being developed. The scheme uses a distributed network of “pins” fabricated from recycled plastics and other waste materials to provide positive reinforcement of a soil mass. Although the application is similar to stabilization of slopes with soil nails or micropiles, significant modifications to conventional design and construction are necessary to account for the reduced strength and increased ductility and creep exhibited by plastic materials compared with concrete and steel. Using recycled plastics has the advantage of providing reinforcing members with low susceptibility to degradation and provides a market for materials that otherwise might be buried in a landfill. An extensive investigation is under way to evaluate the potential for using recycled plastic pins (RPPs) to stabilize minor slope failures. This evaluation includes quantification of appropriate material and engineering properties of RPPs, evaluation of RPP resistance to degradation in various environments, development and evaluation of suitable mechanisms for installing RPPs, evaluation of RPP resistance to driving stresses, development of a design procedure that accounts for the reduced structural capacity of RPPs compared with steel or concrete members, and installation and monitoring of several full-scale field demonstration sites. The ongoing evaluation program that is described focuses on laboratory tests to determine fundamental engineering and material properties, field driving trials to evaluate potential driving mechanisms, and preliminary development of a suitable procedure for designing RPP stabilization schemes.

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An ongoing demonstration project has shown the feasibility of using slender (90 mm × 90 mm × 2.4 m) recycled plastic pins (RPPs) for in situ reinforcement of slopes and embankments. The technique uses RPPs driven into the face of the slope in a grid pattern to intercept the sliding surface and “pin” the slope. The engineering properties of the RPPs, including the compressive, tensile, and flexural strength along with creep behavior, dictate the design and construction practice. Constituent materials and manufacturing processes are highly variable among the more than 30 U.S. manufacturers. A specification for acceptance of the members is needed; however, before an effective specification can be developed, the appropriate engineering properties and design requirements for the RPPs must be determined. The engineering properties and driving performance of four different types of members were evaluated and are reported on. Additional evaluations are under way.

Surficial slope failures, or nuisance slides, constitute a significant economic and manpower burden for many transportation agencies because of the frequent and recurring nature of the slides. TRB recently estimated that annual costs for stabilization of nuisance slides exceed the costs for repair of major landslides; this estimate suggests that annual costs for repair of nuisance slides on the National Highway System alone exceed $100 million. Recent work has shown the feasibility of using slender recycled plastic members for in situ reinforcement of surficial slides in slopes and embankments. This paper describes the activities performed to evaluate the technique and the results and conclusions derived from the work. Topics covered include the description of five instrumented field test sites, material properties of the recycled plastic members used, construction equipment and techniques used to install the members, general performance observed at the field test sites, and the costs of the technique as compared with other methods.