Deeply Buried Thermoplastic Pipe Field Performance over Five Years

Abstract

This paper presents the updated long-term field performance data from the thermoplastic pipe deep burial study that the writers first initiated in the summer of 1999. The data from the past four to five years are presented in terms of pipe deflections and soil pressure measured at the pipe crown. Examinations of the historic field performance data revealed pipe-soil interaction behavior that had not been reported previously. The long-term pipe performance of both polyvinyl chloride and high density polyethylene pipes installed under at least 6.1 m (20 ft) of soil fill was characterized with nearly constant deflections/circumferential shortening and fluctuating soil pressures. Review of the long-term soil pressure data revealed some interesting trends regarding the relationships among pipe material type, pipe wall design, and fill height. Detailed review of the soil pressure data also led to a reasonable speculation that the seasonal fluctuations of environmental (air temperature, soil moisture) conditions caused the fluctuations in the peripheral soil pressure. Theoretical analysis based on the full-field elastic solutions showed that the temperature most likely had a much larger influence on the soil pressure fluctuations than the changes in the soil moisture conditions.