Finite-element analysis applied to flexible pipe systems requires capabilities not included in conventional finite-element analysis computer programs. Because of the flexibility of the fiberglass-reinforced plastic pipe and other pipes of similar flexibility, the finite-element analysis may need to accommodate large deflections. In addition, the sensitivity of the pipe and the soil properties to compaction loading should be considered. In this study the stress history of the soil elements was monitored at each loading increment to determine whether each element was to be analyzed by using primary loading nonlinear elastic parameters or unloading and reloading stress-dependent elastic parameters. The development of the additional features of the finite-element computer program allowed for applications to buried flexible pipe when subjected to various installation conditions, backfill material types, surcharge loadings, and internal pressurization. Results of the finite-element analysis applications were compared with measured pipe responses from similar soil-box installation conditions. The features of the finite-element analysis computer program and results for a silty sand backfill material under several installation conditions are described. The results are compared with the measured response of the pipe from soil-box tests.

Finite-element analysis (FEA) has been used for several years to predict the response of buried pipes. Several computer programs have been developed that specifically analyze soil-structure systems (l-3; 4, pp. 425-430). The development and use of finTt;-element techniques to analyze the response of buried flexible fiberglass-reinforced plastic (FRP) pipe are described. The response of the pipe when subjected to various installation and static loading conditions as computed by the finite-element method was compared with measured strains and deflections taken from physical tests in a soil box at the Buried Structures Laboratory at Utah State University. The finite-element soil-structure system modeled the actual soil-box installation conditions. The stress-strain soil parameters that were used in the FEA were obtained from triaxial shear tests performed on the soils used in the soil box.