Geosynthetic Reinforcement to Protect Underground Pipes against Damage from Construction and Traffic
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2016-02-01
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Abstract:Shallowly buried pipes are subjected to surface loading, such as construction and traffic loading, and they may be damaged due to excessive loading and penetration by excavation equipment. A number of pipe incidents happened in the United States and around the world that resulted in fatalities, injuries, and significant property damage and loss. Therefore, protection of underground pipes against damage from construction and traffic are important and necessary. Unfortunately, no effective method is available so far. This proposed research was to develop a technology using geosynthetic reinforcement to protect underground pipes (either existing or new pipes)against damage from construction or traffic. The geosynthetic reinforcement is laid across the trench between the surface and the top of the pipe. The objective of this proposed research was to evaluate the level of protection provided to a steel-reinforced HDPE pipe by geogrid. Seven static plate load tests, three cyclic plate load tests, and five rod penetration tests were conducted on shallowly-buried steel reinforced HDPE pipes in the large geotechnical box (3 m x 2 m x 2 m) at the University of Kansas. Of the fifteen tests, five tests were run without geosynthetic as control sections for comparison to the geogrid-reinforced sections. Two backfill materials were used, which included a compacted sand backfill and a poured aggregate backfill. For all tests the in-situ soil was a fat clay. Earth pressure cells, displacement transducers, and strain gauges were installed around or on the pipe and the geosynthetic to investigate the effects of the geogrid and the backfill on the pipe performance and the surface deformation. The analysis of test results shows that the type of backfill had an important effect on the pipe performance and the surface deformation and the benefits of geogrid reinforcement. Under static and cyclic plate loading tests, the geogrid placed underneath the base course was more effective in reducing the settlement of the plate, the vertical and horizontal deflections of the pipe, and the vertical earth pressures at the pipe crown and invert than that placed inside the trench. The inclusion of geogrid improved the distribution of earth pressures around the pipe and resulted in more uniform deformation of the pipe and minimized the bending of steel ribs at the pipe crown. Under static and cyclic plate loading tests and rod penetration tests, the geogrid provided lateral restraint to soil particle movement and reduced the longitudinal strains in the pipe liner. Geogrid reinforcement above the pipe increased the rod penetration resistance at the constant penetration depth or reduced the penetration depth under the same force. The inverted U-shape geogrid and wrapped-around geogrid layouts were more effective than the single and double geogrid layouts.
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