Behavior of Large-Diameter Buried Pipes—A Case Study of a Parallel Trench Excavation

The behavior of buried flexible pipes is one of the complex soil-structure interaction (SSI) problems in geotechnical engineering. Additionally buried pipe system exposed to parallel trench excavation is special design situation and requires careful attention during design in order to avoid unanticipated failures. Present study describes analyses of parallel installation of four numbers of 3,840 mm outer diameter and 20 mm thick buried mild steel pipes to study influence of the parallel trench excavation, hydro test load, unanticipated rainfall and different backfill/bedding properties on the deformation of buried pipes. Staged construction method was adopted in geoslope (Sigma/W) analysis for investigation of the displacement response of pipe. The pipe was modeled as a structural beam element with 5 bar internal operational pressure, hydrostatic water pressure due to ground water and self-weight. The effect of parallel trench excavation on one side of the pipe installation was analyzed and distributions of pipe deflection at each stage were monitored. Additionally, the different pipe bedding properties were considered in order capture the effect of modulus of soil reaction on the pipe displacements. The stresses along the half perimeter of the pipe are compared to differentiate the difference in the surrounding reaction/pressure. The results were discussed and are compared with performance and deformation of the pipes actually installed at site. Study highlights that current design recommendations as per AWWA M11 (2004) or equivalent does not provide sufficient guidance for such special design situations and recommends further research in order to provide sufficient design recommendations which can be practiced confidently.