South Australia & NT Chapter

Flexible uPVC Pipes in Trenches with Stiff Clay Walls Subjected to Construction Traffic

Dr. Don Cameron

This presentation described numerical modelling of field tests involving traffic loading on flexible uPVC pipes buried in sand within trenches formed in stiff clay. The tests were part of a commissioned program to verify safe cover heights for the spirally-wound, uPVC pipes. The modelling was performed using three-dimensional finite elements with the backfill soil represented by a state parameter model. A constitutive model for the sand was described, which was based on the state parameter concept.

Single element modelling of the triaxial tests provided a set of appropriate soil material constants. The constitutive model was incorporated into a finite element analysis program (AFENA) and applied to the simulation of a plate-loading test on a confined sand volume; the simulation compared well with experimental data. The Finite Element Analyses were then extended to the modelling of the buried pipe tests both in the laboratory and in the field. Only the four field tests were reported on this presentation.

A major difficulty was identified with current simplified methods of estimating deflections of pipes buried in trenches and subjected to construction loading; prediction of the stress distribution above a pipe is difficult with a yielding backfill. A preliminary method of estimating stresses was proposed, based on results from the finite element analyses, which can be used with simple methods of calculating pipe deflections.

Dr. Don Cameron is a Senior Lecturer at the University of South Australia, School of Natural and Built Environments with extensive experience in both practical and theoretical geotechnical engineering.

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