Long-term monitoring of pipe under deep cover

Cover title.; "September 2007."; Executive summary laid in.; Includes bibliographical references (p. 99-102).; Final report.; Performed by Ohio Research Institute for Transportation and the Environment (Dept. of Civil Engineering, Ohio University) for the Federal Highway Administration and Ohio Dept. of Transportation Office of Research and Development; Harvested from the web on 8/2/11In the study described in this report, the ORITE research team monitored from 2000 to 2005 the field structural performance of the eighteen thermoplastic pipe structures at the deep burial project site located in Albany, Ohio. In the fall of 2004, the team introduced controlled cuts or notches to the select pipe structures and recorded the pipe wall responses to the defects using strain gages. The team also removed small coupon specimens from the end sections of the select 7-year old thermoplastic pipes and examined them by the standard tensile modulus/strength test method in the laboratory. The long-term field data indicated that the pipe deflections had been fairly stable since the first year, while the soil pressures acting around the pipes had been fluctuating seasonally in each year. According to theoretical analysis, seasonal changes in the air temperature were responsible for the soil pressure fluctuations, not the seasonal changes in the soil moisture conditions. During the in-situ notching experiments, strains induced in the pipe wall by the notching process always disappeared quickly within 10 seconds. There were no signs of slow crack growth observed. This was even true for the longitudinal cuts made at the crown, where tensile stresses usually exist. The laboratory tensile strength test results showed that the tensile properties of the thermoplastic did not degrade at all over the 7 year period. Overall, the long-term phase of the ORITE thermoplastic pipe deep burial project showed that stress relaxation tends to govern the field behaviors of the buried thermoplastic pipe than creep. The long-term performance data collected during this unique field study reaffirmed the importance of installing these thermoplastic pipes properly according to the current ODOT specifications