Modeling of Flexible Pipe for Culvert Application under Shallow Burial Condition

Flexible thermoplastic p1pes under field and laboratory loading conditions have been
examined in the present study. The flexible pipes were tested under truck loading
application with shallow soil cover. The pipe-soil system response includes soil stresses
around and above the buried pipes, vertical pipe crown diametral strain, and
circumferential pipe wall strains. Modeling the pipe-soil system is made using plane
strain and thin ring assumptions. A thin ring model using Castigliano's theorem is
developed to analyze the behavior and response of a flexible pipe under well defined
loading conditions and simulate the behavior of the buried pipe under the live load
application. Laboratory work was carried out to study the pipe behavior and response
under two-point, three-point, and four-point loading configurations. The thin ring model
predictions show good agreement with classical solutions specially valid for two-point
and three-point loading configurations. Laboratory results were also in good agreement with the predictions. Laboratory results show that the maximum tensile strain for the
four-point loading test occurs at inner pipe crown region. Comprehensive efforts were
made to correlate the thin ring model predictions with the field test results; however, it
appears that the thin ring model cannot be used to simulate the effect of the live load
application. A major source of the differences between the predicted and measured
values is attributed to the applied load magnitude. A further investigation was carried out
to examine the applicability of the model to study the general pipe behavior. The
predicted hoop pipe wall strain profile was found to be similar to that of the reported
strain profile by Rogers under overall poor soil support condition. Comparison of soil
stress distribution shows that the 2D prediction approach provides nonconservative
results while the FE analysis agrees more favorably with the measured pressure data.
Overall, FE analysis shows that a linearly elastic isotropic model for the surrounding soil
and flexible pipes with a fully bonded pipe-soil interface provides a reasonable prediction
for soil pressures close to the buried pipes.