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Lateral loading experiments for buried pipe in reinforced ground with geogrids under different hydraulic gradient

In internal pressure pipelines, thrust force acts on the pipe bends constantly, and displacement of the buried pipe is supported by passive earth pressure. It has been reported that the pipe bends largely displaced and separation of pipe joints occurred since lateral resistance force was reduced in liquefied ground. In Japan, the improvement of seismic resistance is strongly required because it is expected that the severe earthquake occurs in the near future. As a countermeasure against liquefaction, Japanese current design standard for irrigation pipelines suggests the method that pipelines are partially backfilled with gravel to enhance the capability of dissipation of pore water pressure. In addition, the past researches show that thrust restraints using geogrids and gravel in liquefied ground are very effective since pull-resistive stress of the geogrids prevents the displacement of bent pipe. However, the details of the design methods about the appropriate installation area of gravel and geogrids are still not clear, and the specific guideline for practical usage is not established. In the present study, the lateral loading tests are carried out in order to correct the knowledge which contributes to developing the liquefaction countermeasures using geogrids and gravel. The test results show that the countermeasure method which integrated the gravel surrounding the pipe was the most effective to enhance the shear resistance force against the displacement of the pipe.