Pennsylvania Thermoplastic Pipe Deep Burial Project: 20th Year Investigations

In June of 2007, the Ohio University research team visited the $610\text{-}\mathrm{mm}$ $\left(24\text{-}\mathrm{in.}\right)$ diameter corrugated high density polyethylene (HDPE) pipeline structure located under $30.5\text{-}\mathrm{m}$ $\left(100.0\text{-}\mathrm{ft}\right)$ high embankment of Interstate Highway 279, near Pittsburgh. This visit marked the 20th year of the field research project. The team conducted visual inspections of the pipeline along with in-situ pipe drilling experiments. The in-situ pipe wall drilling experiments conducted at the site induced strains in the pipe wall. However, the strains dissipated completely within $5\mathrm{s}$ . This demonstrated the nature of the viscoelastic material and a lack of significant stress levels existing in the pipe wall. These in-situ pipe wall drilling experiments are an innovative procedure for showing the stress relaxation capability of HDPE. Localized cracking of the pipe end was observed at joints positioned under more than $21.3\mathrm{m}$ $\left(70.0\mathrm{ft}\right)$ soil fill and where two sections of Type C pipe were connected. The cracking observed in 2007 appeared to show insignificant changes from those observed during the 2002 inspections. No signs of structural distress were detected inside pipe sections that were under less than $21.3\mathrm{m}$ $\left(70.0\mathrm{ft}\right)$ of soil fill. The pipe deflections, which were measured under $30.5\mathrm{m}$ (100.0 ft) of fill, have been stable for a number of years. The horizontal deflection changed by only 0.3% over the past $17\text{years}$ . The vertical deflection has hardly changed over the past 18 years. The pipe circumferential shortening has increased by less than 0.2% over the last 18 years. Finally, the results of the laboratory tests showed that no noticeable changes took place in the basic engineering properties of the HDPE pipe material over the past 20 years.