Papers # 2014 Chicago
Corrugated HDPE pipes are an attractive product for culvert and drainage applications in the railroad industry due to their resistance to corrosion and abrasion, long service life, and flexibility. Currently, these pipes are required to be manufactured with 100% virgin materials. However, therail industryhas recently expressed interest in using pipes made with recycled content due to the environmental and economic benefits of these pipes. Corrugated HDPE pipes manufactured with recycled content have been used successfully in agricultural and other land drainage applications for many years, but these pipes typically do not have the severe service loads associated with railroad applications.
One of the primary areas of concern with incorporating recycled materials into corrugated pipesin severe shallow-cover railroad applications is the potential for contamination from the recycled material stream that could make its way into the pipe wall and reduce the service life of the pipe. A critically sized contaminantcould act as a stress riser andpotentially lead to stress cracking under conditions of heavy cyclical live loading.To evaluate this concern, corrugated HDPE pipes made with recycled content were installed underneath a transit rail line in northeast Philadelphia with just 2 feet of cover from the top of the pipe to the bottom of the railroad tie. These pipes were instrumented with strain gages and extensometers to record the effects of live loads on the pipe wall. This data was compared to previous data gathered by the Plastics Pipe Institute for freight railroad loading applications. The data sets are being used to develop an accelerated laboratory test to evaluate the long-term performance of pipes made with various blends of recycled materials to determine the effects of contaminants on cyclical live loading in these shallow cover railroad applications.
The data from the instrumented pipes indicates that the dynamic wall strains and deflections in the pipe due to the shallow cover rail loading are very low (less than 0.2% strain was measured in the pipe wall). However, the frequency of loading can be high, with many pipes seeing over 1,000,000 cycles per year and up to 200 cycles per train. The peak tensile wall strains were observed between the crown and springline of the pipe.At the time of this paper, the laboratory testing is not complete, but the methodology for testing and evaluation is being presented along with the live load data evaluation and preliminary results of our research.