Page 204 - Buried Pipe Design

178 Chapter Three

computer programs. Such capabilities include analysis of stress history
of the soil elements to determine whether each element is in primary
loading or in unloading and reloading, modification of the iteration
scheme to better model the soil response when changing from one stress
condition to another, and large deflection theory by modifying nodal coor-
dinates after each load increment.
The development of these features has allowed for analysis of not
only rigid pipe but also flexible pipe with compaction simulation, sur-
charge pressures, rerounding caused by internal pressurization, and
various installation conditions. The results of the analysis of the vari-
ous installation conditions have shown the effects of shoulder and
haunch support on the pipe and suggest that these conditions be con-
sidered in pipe and installation design.
The results of this FEA development program at Utah State
University have improved the modeling capability of flexible pipe sys-
tems. Moreover, an improved understanding of the behavior of the
buried flexible pipe has been developed due to the ability to model var-
ious installation conditions. The results of the overall study, including
the four soil types and various loading conditions, have shown a very
good correlation between FEA results and the measured responses
from the physical model tests. This has given strong justification for
the use of the finite element method to adequately model various
installation conditions, soil materials, loading conditions, pipe sizes,
and so forth, without the additional expense of performing extensive
physical tests. However, calibration of the FEA model required the
results from physical tests. Finite element analysis, along with exper-
iments, has resulted in a better analytical tool for the evaluation of
buried pipe performance. This tool is now available and is being used
primarily for research and analysis. It is the design tool of the future.

References
1. Asphalt Institute. 1997. Soils Manual for the Design of Asphalt Pavement
Structures. Manual Series No. 10 (MS-10). Lexington, Ky.
2. Bishop, R. R. 1981. Time Dependent Performance of Buried PVC Pipe. In
Proceedings of the International Conference on Underground Plastic Pipe,
pp. 202–212. New York: American Society of Civil Engineering Conference.
3. Burns, J. Q., and R. M. Richard. 1964. Attenuation of Stresses for Buried Cylinders.
In Proceedings of the Symposium on Soil Structure Interaction, pp. 378–392. Tucson:
University of Arizona.
4. CANDE-89, Culvert ANalysis and Design computer program/ User Manual, Federal
Highway Administration; Publication No. FHWA-RD-89-169, June 1989.
5. Chambers, R. E., and F. J. Heger. 1975. Buried Plastic Pipe for Drainage of
Transportation Facilities. Cambridge, Mass.: Simpson Gumpertz and Heger, Inc.
6. Duncan, J. M., P. Byrne, K. S. Wong, and P. Mabry. 1980. Strength, Stress-Strain
and Bulk Modulus Parameters for Finite Element Analysis of Stresses and
Movements in Soil Masses. Report No. UCB/GT/80-01. Berkeley: University of
California Office of Research Services.