Abstract:
Surfacc load due to vehicular traffic influences the performance of shallow buried
pipcs. This thcsis prcscnts an invcstigation of the behavior of buried flexible pipes
due to surlacc load. Two-dimensional finite element analysis was performed
through idealization of the concentrated surface load as an equivalent line load. A
general purpose f1nite clement program ABAQUS was used for modeling of the
pipe-soil intcraction under surface loads. Finite element model was developed and
evaluated using full scale test data of buried flexible pipe from the literature,
where responses of buricd flexible pipe were measured under surface live loads.
Through a comprehensive study on different parameters of buried structure under
different burial depth, it was observed for large diameter flexible pipe that
influences of surface loads are localized within a zone around the pipe crown for
shallow buried pipes «0.5D) and for pipes with low material modulus. However,
the influence extends downward covering the full pipe circumference for deeper
pipes and pipes with high material modulus. For a particular pipe, the effects of
the surface load reduced rapidly with the depths of soil cover up to a depth of half
of thc pipe diametcr, beyond which the effect reduced steadily. The conccntrated
sur/ace load induces compressive wall thrust and negative bending moment
(outward concave bending) at the shoulder, and positive bending moment
(outward concave bending) at the crown and invert.
The study revealed that the effects of the concentrated surface load depend on the
burial depth, pipe material, and geometry of the pipe wall. Although sectional area
of pipe wall do not affect largely, moment of inertia of pipe wall affect the thrust
and moments that develop around the pipe. The effects are very significant on the'
dcvelopment of bending moment. Material modulus of pipe also affects the thrust
and moment developing around the pipe circumference. However, the influence is
small on the thrusts, while the bending moment is significantly affected. The
maximum momcnt induccd duc to surface load can be expressed as a function of
the relative bending stiftlless of the pipe-soil system. The mechanism of the stress
development around the pipe was found different for shallow and deep burial
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conditions lor High-Density polyethylene (HOPE) pipe. Boussinesq solution
always over-predicted the crown level stress Jor HOPE pipe. However lor the
stiffer (steel) pipe, Boussinesq equation under predicted the stress. These are due
to development of arching from soil-pipe interaction that is not captured in
lloussincSl(s cquation. AASHTO. AseE codc yielded conservative valucs of the
average soil strcsscs lor pipcs with greater burial depths.
