The induced trench method—a critical review and case history

Abstract

The "induced trench" method for buried pipe protection is reviewed. By installing a zone of relatively compressible material within the backfill above a pipe, soil arching is induced. This has the effect of reducing the vertical earth load on the pipe, permitting the pipe to be buried at a greater depth than would otherwise be tolerable. In many circumstances, the method can offer significant economic benefits over alternatives. Although the literature includes several case histories describing the use of this technique, geotechnical aspects have received little attention. The theory on which currently available design methods are based is somewhat outdated and fails to address many factors that affect performance. For a recent project in Calgary, Alberta, a nonlinear finite element simulation was carried out to optimize the design. Performance during and after installation was monitored. Vertical pressures on the pipe were significantly less than those predicted by conventional theory. There is a need for the development of a more rational approach that is suitable for routine design. Key words: induced trench, soil–structure interaction, buried pipes, soil arching.