An investigation of the behavior of buried flexible pipes in nonuniform backfill materials

Due to population growth, new residential areas are being established. In this regard, depending on basic needs, high-density polyethylene (HDPE) pipe usage is increasing day by day in oil and gas pipelines, drinking water, irrigation, wastewater networks, solid matter transportation and drainage applications. HDPE pipes are widely preferred and the indicators of this trend are long service life, flexibility, high corrosion and fatigue resistance, smoothness, easy installation and jointing, using in a wide range of temperatures, economical, electrical insulated, taste and odor-free, environment friendly. In this Ph.D. dissertation, the deformation behavior of HDPE pipes in silica sand backfill was investigated experimentally and numerically under different relative density conditions (75%, 60% and 45%). Diameter, wall thickness and length of the HDPE pipes equipped with strain gauges are 400 mm, 9.8 mm and 1500 mm, respectively. As a result of comprehensive laboratory tests and ANSYS finite element software outputs, failure conditions were observed in critical sections which are crown and springlines related to deformations. In this context, under the different relative density conditions, half-section waste vehicle tires were fitted on the pipe in critical sections and along the pipeline for reinforcement. In the strengthening experiments, it was observed that the deformation and bending moment values significantly decreased in the regions where half-sections waste vehicle tire reinforcements were used. In the tests where waste vehicle tires were applied in critical sections, less deformations were observed between 45% and 51% in the crown and 57% and 69% in the springlines. Additionally, the use of recycled granular rubber layers from waste tires as an absorber layer in the upper region of the backfill and bedding material was investigated. As a result of the investigations, the advantages of half-section waste vehicle tires used on the pipeline were demonstrated by extensive laboratory tests and numerical analysis.