Sustainable Slope Stabilization Using Recycled Plastic Pin In Texas

Abstract

Shallow slope failures are predominant in the North Texas area and pose significant maintenance problems for the Texas Department of Transportation (TxDOT). As a cost effective alternative, the Recycled Plastic Pin (RPP) can be utilized to stabilize the shallow slope failure. RPP are fabricated from recycled plastics and waste materials (i.e. polymers, sawdust, and fly ash). It is a lightweight material and less susceptible to chemical and biological degradation than alternative reinforcing element. RPPs are driven into the slope face, which provide additional resistance along the slip surface and increase the factor of safety. The current study summarized the remediation of shallow slope failure using RPP. Two highway slopes, one located over US 287 near the St. Paul overpass in Midlothian and one over Loop 12 near the UP RP rail overpass in Dallas, Texas were stabilized using RPP. Three 50 ft. sections were selected and reinforced using RPP after a crack, caused by slope movement, was observed over the shoulder in the US 287 slope. Two 50 ft. control sections were placed between the reinforced sections to compare the performances of the slope. A 50 ft. section over top slope and a 100 ft. section at the bottom slope of Loop 12 were reinforced with RPP as a temporary solution. The field performance of the slope was monitored using instrumented RPPs, inclinometers and surveying instruments. The performance monitoring results of US 287 slope indicated that the unreinforced control sections had significant settlement at the crest of the slope, as much as 15 inches. In addition, a total of 3 inch increments in settlement had taken place during the year. In contrast, almost no increment in settlement was observed at the reinforced section in US 287 slopes. Moreover, the total settlements in the reinforced sections were 2 inch to 4 inch which was less compared to the unreinforced sections. The horizontal displacement of the US 287 slope had taken place after 1 year of construction which ranged up to 1.5 inch. After 1 year, the horizontal displacement became less than 0.1 inch at the Reinforced Section 1. The performance monitoring results of the Loop 12 slope presented that the top of the retaining wall is still moving after the installation of RPP. However, RPP installed adjacent to the footing provided lateral resistance and restricted the sliding of the wall. The maximum resistance was observed with closer RPP spacing. The cost analysis for the US 287 slope indicated that the cost for slope stabilization using RPP can be 50% lower compared to the cost of conventional slope stabilization approaches. The performance of the US 287 slope was further evaluated in numerical study and a parametric study was conducted to evaluate the effect of length and spacing of RPP which indicated that the deformation of reinforced slope increase with wider RPP spacing. Finally, a performance-based design method was developed to design the slope stabilization for surficial failure. The design method considers three limiting criteria which consider restricting failure of soil, limit horizontal displacement of RPP and limit maximum flexure in RPP. Based on the design method, the calculated factors of safeties were in good agreement with the safety analysis results in numerical study.