Investigation of the effects of vertical and lateral loads on the stability of buried pipes

In recent years there has been increasing use for flexible pipes in many areas such as natural energy transportation pipelines, water distribution or waste water drainage systems etc. However, much of the soil-pipe behavior and pipe performance under various conditions has not been fully understood. In order to identify the complex soil- pipe interaction and pipe performance under different backfill and loading conditions, an experimental set up was designed at Yıldız Technical University Geotechnical Engineering Laboratory. Experiments were performed in a soil box which simulated a flexible buried pipe in trench conditions. Dry and poorly graded sand as backfill material and three HDPE buried pipes, diameters ranging between 200-312 mm were used in the investigation. A comprehensive study was carried out to determine the effect of backfill installation, backfill relative density and loading conditions on the pipe deformation and pipe stability. Furthermore, backfill materials have been placed to the soil box at different void ratios to provide different relative densities. Loadings were applied with increments of 10 kPa up to 300-500 kPa in vertical axis using an air pressure membrane. At each loading step vertical and horizontal deformations at pipe cross section were measured by means of Lineer Position Transducers. The experimental set up have been modeled by utilizing finite element analysis program named PLAXIS 2D and PLAXIS 3D TUNNEL programs. Modifiyed Iowa Emprical Methods have been used to determination of the pipe deflections under various conditions. Experimental and numerical solutions are compared in order to evaluate the soil pipe interaction problem. Keywords: Buried Pipes, Laboratory Tests, Finite Element Methods, Photogrametric Measurements