Dune sands cover vast areas in Oman and create major problems for construction of infrastructures. Also suitable backfill soils for construction of buried pipes are not available in these areas. Plastic buried pipes are in use for decades but their performances are not well understood. This paper investigates the performance of thermoplastic pipes installed in dune sand. It simulates the problem as a two dimensional plane strain finite element model by using AQUS/CAE, Version 6.1. The proposed model considers only one half of the system because of symmetry of the problem. The mesh extends horizontally 3-D (where D is the pipe diameter) from pipe center, 1.5-D below the invert and 2-m above the crown. Complete fixity was enforced at the lower edge of the mesh. Roller support was used at both vertical sides of the mesh. A hypoelastic constitutive model was used for soil. Full bonded or contact or slip elements were employed at pipe-soil interface. The pipe soil system response includes percentage change in vertical diameter, thrust, bending moment and shear stresses around the pipe. The study considers different factors that affect the pipe-performance such as relative density (dense, medium dense and loose dune sand soil), pipe material (i.e. HDPE, PVC) and soil cover on the performance of plastic pipes installed in dune sand. The study shows that these parameters have a large influential effect on the performance of thermoplastic pipes. For example, all the pipe responses (e.g. change in vertical diameter, thrust and bending moment) increase with the increase in relative density of soil and the increase in soil cover. The effect of pipe material is not as significant. There is a slight difference in percentage in vertical diameter for PVC and HDPE pipes, although the modulus of elasticity of PVC is larger than that of HDPE. However, the thrust and bending moment induced in PVC are larger than those induced in HDPE. However, the opposite is true for the bending moment. The main conclusion of this study is that medium-dense to dense-dune sand can be used as a backfill material for thermoplastic plastic pipes. The predicted changes in vertical diameter using these backfills are much less than the typical specified value of 5%.
展开▼
