عنوان مقاله [English]
With increase in cities’ population and development of urbane life, passing buried pipelines near ground’s surface is inevitable in urban areas, roads, subways and highways. This paper describes the results of laboratory tests conducted on flexible uPVC pipes with diameter of 160 mm, buried in unreinforced and reinforced trench with geogrid layer and expanded polystyrene (EPS) geofoam block. To simulate the semi-heavy vehicle loads, the repeated load with amplitude of 450 kPa and frequency of 0.33 Hz was applied on the trench surface, using plate loading at a diameter of 150 mm. Vertical diameter strain (VDS), strain at pipe’s crown and transferred pressure on the pipe’s crown and springline were recorded throughout the test for up to 500 cycles of loading. The variables examined in the testing program include thickness of EPS block (30, 60 and 100 mm), width of EPS block (160 and 240 mm) and embedment depth of pipe. In the unreinforced tests, the pipes were embedded at depths 1.2, 1.5 and 2.0 times their diameter, while in the reinforced tests with geogrid layer and expanded polystyrene (EPS) geofoam block with density of 20 and 30 kg/cm3, the pipes were embedded at depths 1.2 and 1.5 times their diameter. The results show that the values of VDS and pipe strain increased rapidly during the initial loading cycles, thereafter the rate of deformation and strain reduced significantly as the number of load cycles increased. In the geogrid reinforced system, the vertical diameter strain (VDS) and circumferential crown strain of the buried pipe at the end of the loading cycle have 19% and 20% reduction respectively, as compared with the unreinforced system. According to the results, the minimum VDS and pipe’s crown strain were provided by placing the pipe in depth of 1.5D and using EPS block with 100 mm thickness, 240 mm width and 30 kg/cm3 density over the pipe in addition to a geogrid layer giving values of, respectively, 0.26 and 0.3 times those obtained in the reinforced trench with a geogrid layer.