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Effect of geofoam location and density on the improvement of buried flexible pipe

In this study, the effects of geofoam location and density for buried pipelines is investigated in laboratory physical model tests. Experiments are conducted in a box having 1 m x 1 m area and 0.6 m height, where a clean sand is used as the bedding and surrounding material. A 20-cm-diameter PVC pipe is positioned on a 10-cm-thick bedding soil layer, and above the pipe EPS geofoam plates with two different densities are placed with varying distances from the pipe crown (0, 5 and 10 cm above the crown). Incremental static loading is applied to the ground surface via a circular steel plate (such as in a plate load test) and vertical deformation of the pipe, as well as that of the ground surface, are measured. Geofoam creates a compressible zone over the pipe, which initiates soil arching and transfers the load above the pipe to surrounding soil. It is seen that introduction of geofoam improves the pipe deformation behavior provided that geofoam does not yield. Moreover, it is observed that better improvement is achieved when geofoams are placed closer to the pipe crown. When different density EPS plates are considered, lighter density EPS acts as better compressible inclusion, hence shows better improvement on pipe for lighter surface loads. However, it is seen that denser geofoam shows improvement for a wide range of applied stress compared to EPS with lower density.